USING THE STEADY/PULSED-PEDESTAL PARADIGM TO STUDY VISUAL …

USING THE STEADY/PULSED-PEDESTAL PARADIGM

TO STUDY VISUAL ATTENTION

by

BENJAMIN AARON GUENTHER

(Under the Direction of James M. Brown)

ABSTRACT

Researchers continue to explore the relationship between different attention phenomenon and the

sensory nature of the stimuli; however, this relationship is still not well understood. The steady-

and pulsed-pedestal paradigm (S/PP paradigm) is a simple and flexible stimulus manipulation

influencing relative processing along transient and sustained channels. The purposes of the

present experiments were to first, evaluate the effectiveness of this paradigm when simple

reaction time (RT) was the dependent measure, and second to further explore the relationship

between transient and sustained channel activity and two common attention effects, the object

advantage and inhibition of return (IOR). The S/PP paradigm produced a consistent pattern of

effects across both attention paradigms with pulsed-pedestal conditions having a greater

influence on RTs to invalidly cued targets. This resulted in an increased validity effect in an

object-based attention experiment and decreased IOR magnitudes. Results indicated, first, the

S/PP paradigm can be effectively used with RT as a dependent measure. And secondly, the S/PP

paradigm (a task-irrelevant manipulation) has a different influence on attention than previously

used task-relevant manipulations. Additionally, future theories and accounts for IOR and the

object advantage need to be able to address the sensory influences revealed through

manipulations of relative processing of transient and sustained channels.

INDEX WORDS: Visuospatial Attention, Inhibition of Return, Object Advantage,

Magnocellular and Parvocellular Visual Pathways, Transient and

Sustained Channels



by


B.S., Washington State University, 2004

M.S., University of Georgia, 2008

A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial

Fulfillment of the Requirements for the Degree

DOCTOR OF PHILOSOPHY

ATHENS, GEORGIA

2011

© 2011

Benjamin Aaron Guenther

All Rights Reserved



by


Major Professor: James M. Brown Committee: B. Randy Hammond Robert P. Mahan Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia May 2011

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. James M. Brown, for his mentorship throughout

this process. I would also like to thank the other members of my committee, Dr. B. Randy

Hammond and Dr. Robert P. Mahan for their advisement on this project.

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TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ........................................................................................................... iv

LIST OF FIGURES ...................................................................................................................... vii

CHAPTER

1 INTRODUCTION .........................................................................................................1

P and M Pathways ....................................................................................................1

Transient and Sustained Dual-Channel Perspective ................................................3

The Steady/Pulsed Pedestal Paradigm .....................................................................5

Attention and P and M Activity ...............................................................................7

Object- and Space-Based Attention .........................................................................9

Inhibition of Return ................................................................................................16

Using the S/PP Paradigm to Study Visual Attention .............................................17

2 EXPERIMENT 1 .........................................................................................................21

Method ...................................................................................................................22

Results and Discussion ..........................................................................................23

3 EXPERIMENT 2 .........................................................................................................25

Method ...................................................................................................................27


4 EXPERIMENT 3 .........................................................................................................31

Method ...................................................................................................................32

v


5 EXPERIMENT 4 .........................................................................................................35

Method ...................................................................................................................36


6 GENERAL DISCUSSION ..........................................................................................40

Object Based Attention ..........................................................................................46

Inhibition of Return ................................................................................................47

Conclusions ............................................................................................................49

REFERENCES ..............................................................................................................................51

APPENDX

A ANALYSES OF DATA EXCLUDED FROM EXPERIMENT 4 ..............................60

vi

vii

LIST OF FIGURES

Page

Figure 1: Example of a Pedestal ....................................................................................................61

Figure 2: Experiment 2 Trial Sequence .........................................................................................62

Figure 3: Example of a Traditional 4 Box Stimulus Design ..........................................................63

Figure 4: Example of a modified S/PP Paradigm ..........................................................................64

Figure 5: RT data for Experiment 1 ...............................................................................................65

Figure 6: RT data for Experiment 2 ...............................................................................................66

Figure 7: Effect of the Pulsed Condition on RTs in Experiment 2 ................................................67

Figure 8: Experiment 3 Trial Sequence .........................................................................................68

Figure 9: Effect of the Pulsed Condition on RTs in Experiment 3 ................................................69

Figure 10: RT data from Experiment 3 ..........................................................................................70

Figure 11: Experiment 4 Trial Sequence .......................................................................................71

Figure 12: RT data from Experiment 4 ..........................................................................................72

Figure 13: Effect of the Pulsed Condition on RTs in Experiment 4 ..............................................73

CHAPTER 1

INTRODUCTION

As we look about and visually interact with our environment, lower-level (bottom-up)

sensory processes combine with higher-level (top-down) cognitive or attentional processes to

provide our visual experience. In exploring the link between the structure and function of the

visual system and the higher-level cognitive processes underlying visual attention, one question

that can be asked is how does the nature of the visual stimulus influence attention? One way to

address this issue is through the use of stimuli that take advantage of the differences in

information preferentially processed by the magnocellular (M) and parvocellular (P) visual

pathways (or the transient and sustained channels). If stimuli are manipulated to preferentially

activate one pathway/channel over the other, then greater insight into the relationship of lower

level visual processes in visual attentive processes can be gained by observing differences in the

performance in attentional tasks.

P and M Pathways

The M and P pathways begin in the retina with midget (PC cells) and parasol (MC cells)

ganglion cells. Of the different cell types in the retina, midget ganglion cells (PC cells) project

along the P pathway (e.g., Leventhal, Rodieck, & Dreher, 1981; Perry, Oehler, & Cowey, 1984),

are smaller, have smaller receptive fields (e.g., Shapley & Perry, 1986), and dominate near the

fovea (e.g., Dacey, 1993), compared to cells projecting along the M pathway. Thus, a

characteristic feature differentiating the P and M pathways is their preferential processing of high

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and low spatial resolutions respectively (e.g., Breitmeyer & Ganz, 1976; Livingstone & Hubel,

1987, 1988).

The processing of color information primarily occurs along the P pathway while the M

pathway has limited sensitivity to color information. PC cells are color opponent (e.g., Gouras,

1968; Kaplan & Shapley, 1986; Schiller & Malpeli, 1977) and are present in higher numbers

(e.g., Croner & Kaplan, 1995; Masland, 2001), more densely packed, and consist of smaller cell

bodies and dendritic trees (e.g.,Shapley, 1990) than MC cells. MC cells are generally considered

to have a broad-band spectral sensitivity (e.g., Gouras, 1968; Schiller & Malpeli, 1977) although

only about half are truly broad-band (e.g., Shapley, 1990). The rest, as indicated by Shapley

(1990) are color-opponent cells like the Type IV cells described by Wiesel and Hubel (1966)

consisting of an excitatory center that is broad-band but with an inhibitory surround to long

wavelength (red) light.

While the P pathway is more sensitive to color, the M pathway is more sensitive to

contrast. MC cells typically having much greater contrast sensitivity than PC cells such that MC

cells can respond to stimuli with contrasts as low as 2% while PC cells do not respond well

below 10% (e.g., Merigan & Maunsell, 1993). In regards to these differences, the M pathway

has a contrast response function that is steep at low levels, near threshold, but rapidly saturating

whereas the P pathway has a shallower, near linear contrast response function with increasing

contrast (e.g., Kaplan & Shapley, 1986; Shapley, 1990).

Described above are some of the ways in which the M and P pathways can be

differentiated. Psychophysical techniques can be used to take advantage of these differences.

For example, taking advantage of differences between the M and P pathways sensitivity to

spatial resolution, the spatial frequency of stimuli can be manipulated (e.g., Brown, 2009;

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Brown & Guenther, in preparation). Since, the P system is sensitive to color (whereas the M

system is generally achromatic), the contribution of the M system can be reduced through the use

of equiluminant stimuli (e.g., Brown, Guenther, Narang, & Siddiqui, under review; Cheng,

Eysel, & Vidyasagar, 2004; Steinman, Steinman, & Lehmkuhle, 1997). Additionally, others

have used diffuse red backgrounds to reduce the contribution of the M pathway due the

population of MC cells with inhibitory surrounds to long wavelength light (e.g., Bedwell, Brown,

& Miller, 2003; Yeshurun, 2004). The steady/pulsed pedestal (S/PP) paradigm (e.g., Leonova,

Pokorny, & Smith, 2003; Pokorny & Smith, 1997; Smith & Pokorny, 2003) takes advantage of

another difference between that M and P pathways, their differences in contrast gain (or in their

achromatic contrast response).

Transient and Sustained Dual-Channel Perspective

The present experiments (as well as those in: Brown, 2009; Brown & Guenther, in

preparation; Brown, et al., under review; Guenther, 2008; Guenther & Brown, under review) can

also be described from a transient and sustained dual-channel perspective. This perspective has

been applied to visual perceptual and attention phenomenon occurring at short timeframes such

as visual masking (e.g., Breitmeyer, 1984; Breitmeyer & Ganz, 1976; Breitmeyer & Ogmen,

2006) and transient attention (Yeshurun, 2004; Yeshurun & Carrasco, 1999; Yeshurun & Levy,

2003). The transient and sustained dual-channel perspective emphasizes relative differences in

each channels sensitivity to specific types of stimuli. Transient and sustained channels

sensitivity differences should be considered relative in the sense that one channel simply

outperforms the other with regards to the processing of a specific stimulus property (Breitmeyer

& Ogmen, 2006).

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The transient and sustained channels begin in the retina with MC and PC ganglion cells

which differ in the nature of their response. MC cells have a fast (or transient) response whereas

PC cells have a slower tonic (or sustained) response. Additionally, psychophysical data indicate

the transient and sustained channels have response properties consistent with the M and P

pathways (Breitmeyer & Ogmen, 2006). The dual-channel perspective described here is based

on the model described by Breitmeyer and Ogmen (2006). In their model, transient and

sustained channels are lumped (i.e., considered analogous) with M and P pathways such that

post-retinal areas which receive dominant M and P inputs are lumped with the transient and

sustained channels respectively (Breitmeyer & Ogmen, 2006) .

Illustrating the relationship between the M and P pathways and transient and sustained

channels, transient and sustained channels show different preferences in their response to

stimulus properties such as spatial frequency, temporal frequency, movement, contrast, type of

stimulus onset/offset, as well as flicker frequency (for a review, see Breitmeyer & Ogmen,

2006). In regards to spatial frequency, transient channels have a preference for low spatial

frequencies while sustained channels have a preference for intermediate to high spatial

frequencies (Kulikowski & Tolhurst, 1973; Legge, 1978; Tolhurst, 1973, 1975b). Transient

channels prefer higher velocity movement whereas sustained channels prefer low velocity

movement (Tolhurst, 1973). Transient channels prefer abrupt onsets and offsets (Breitmeyer &

Julesz, 1975; Tolhurst, 1975a) and have a lower threshold for intermediate to high flicker rates

whereas sustained channels prefer either low flicker rates or high flicker rates that are near or

exceeding the flicker fusion threshold (see Breitmeyer & Ogmen, 2006)

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The Steady/Pulsed Pedestal Paradigm

One psychophysical manipulation of the MC and PC pathways is through the

steady/pulsed pedestal paradigm which takes advantage of differences in the achromatic contrast

response of the two pathways (Leonova, et al., 2003; Pokorny & Smith, 1997; Smith & Pokorny,

2003). PC cells have a low sensitivity for achromatic stimulation and their contrast response

function to this type of stimuli is nearly linear with increasing contrast. Whereas MC cells are

highly sensitive to contrast changes, showing a contrast response function that rapidly saturates

with increasing contrast (Kaplan & Shapley, 1986). Taking advantage of the MC cells rapidly

saturating contrast response function, this paradigm uses one condition with a large luminance

transient which drives the MC response towards saturation. This paradigm has been shown to

psychophysically produce MC and PC biased conditions with similar contrast gain, temporal

integration, and spatial contrast sensitivity demonstrated with physiological measures (Leonova,

et al., 2003; Pokorny & Smith, 1997; Smith & Pokorny, 2003).

There are two main conditions in the steady/pulsed pedestal paradigm (sometimes a third,

e.g., Pokorny & Smith, 1997; Smith & Pokorny, 2003), the steady pedestal condition and the

pulsed pedestal condition. In the steady pedestal condition stimuli are presented on a luminance

pedestal which remains on the screen throughout each trial (i.e., a region of the visual field

defined by a different luminance value than the background, see Figure 1). In the pulsed

pedestal condition the luminance pedestal appears briefly with the onset of the target stimulus

(see Figure 2). With brief target presentations, the steady pedestal condition is thought to favor

the M pathway while the large transient onset of the luminance pedestal drives the M pathway

towards saturation (Leonova, et al., 2003; Smith & Pokorny, 2003).

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The steady/pulsed pedestal paradigm has produced consistent results under varying

parameters. It has been modified or adapted several times with each modification or adaptation

producing good M and P biased conditions. For example, while the stimuli used by Pokorny and

Smith (1997) is the most common (a 2x2 array of 1° squares in which one square is the target

stimulus, see Figure 3) others have modified the array such that the pedestal is simply a platform

(Figure 4) on which relevant stimuli can be presented (e.g., Alexander, Barnes, Fishman,

Pokorny, & Smith, 2004; Leonova, et al., 2003; McAnany & Levine, 2007). Additionally, the

size of platform style pedestals has varied greatly. For example, the sizes have ranged from 4°

squares (Leonova, et al., 2003) to a 33.9° x 45.5° rectangle (McAnany & Levine, 2007). While

stimuli tend to be presented around fixation, other studies have used stimuli located peripherally.

For example, Mckendrick and Badcock (2003) used the 4 square array with stimuli centered

12.5° from fixation on the diagonal meridian.

This paradigm has been used to test for M and P functionality in clinical populations with

retinitis pigmentosa (Alexander, Barnes, & Fishman, 2003; Alexander, et al., 2004; Alexander,

Pokorny, Smith, Fishman, & Barnes, 2001; Alexander, Rajagopalan, Seiple, Zemon, & Fishman,

2005), anisometric amblyopia (Zele, Pokorny, Lee, & Ireland, 2007), migraines (McKendrick &

Badcock, 2003), and schizophrenia (Delord et al., 2006). Additionally, this paradigm has been

used to explore M and P contributions to vertical anisotropies in the visual field (McAnany &

Levine, 2007) as well as their contributions to some visual illusions (McAnany & Levine, 2005;

Puts, Pokorny, & Smith, 2005). One area in which this paradigm has not been tested (to the

authors knowledge) is in studies using RT as a measure. With the simplicity and effectiveness of

the steady/pulsed pedestal paradigm at producing M and P biased conditions, it would be a

valuable tool to studies exploring the role of visual attention if was effective with RT measures.

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Although the S/PP paradigm has been discussed in terms of its relation to M and P

functionality (e.g., Leonova, et al., 2003; Pokorny & Smith, 1997; Smith & Pokorny, 2003), it

can also be described in terms of its influence on the transient and sustained channels. In

describing the paradigm in this manner, the pulsed pedestal condition would over stimulate the

transient channels forcing the sustained channels to take a larger role in the processing of the

target stimulus. Looking at it this way, the steady pedestal condition (especially with the nature

of the stimulus design used in the present experiments) would be biased towards transient

channels and the pulsed pedestal condition would be relatively biased towards sustained

channels. For the present experiments, the S/PP paradigm will be discussed from the transient

and sustained dual-channel perspective.

Attention and P and M activity

Previous work exploring the roles of P and M activity in relation to visual attention have

emphasized the importance of the P system. For example, some (Brown, 2009; Brown &

Guenther, in preparation; Brown, et al., under review; Guenther, 2008; Guenther & Brown,

under review; Roth & Hellige, 1998; Srinivasan & Brown, 2006; Yeshurun, 2004; Yeshurun &

Carrasco, 1999; Yeshurun & Levy, 2003) have found evidence illustrating the importance of the

P system in some attention effects. Supporting the notion of an attention system in which P

activity may be more associated with attended processing and M activity more associated with

unattended processing, Srinivasan and Brown (2006) performed an endogenous cuing

experiment using sharp-edged (high spatial frequencies present) or blurred (high spatial

frequencies absent) line segments. They observed, in a simple detection task, typical cuing

effects were present for both target types. However, when the task involved target identification,

typical cuing effects were only found for the sharp-edged target.

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Further support of an attention mechanism favoring P over M processing comes from

studies by Yeshurun and colleagues exploring the influence of transient spatial attention on both

spatial (Yeshurun & Carrasco, 1999) and temporal resolution (Yeshurun, 2004; Yeshurun &

Levy, 2003). Consistent with the smaller receptive fields of P cells (and the notion of an

attention mechanism favoring P processing), Yeshurun and Carrasco (1999) found increases in

spatial resolution at cued locations, showing when attention is drawn to an area, greater detail

can be extracted (or finer judgments can be made) within that area as opposed to when attention

is not drawn to that area. Further work, by Yeshurun and Levy (2003), found that while spatial

attention increases spatial resolution it also decreases temporal resolution which is consistent

with the slower and longer response properties of P relative to M cells. This suggests that when

attention is drawn to an area, it becomes more difficult to distinguish two separate events

occurring close together in time as being separate. To explain this, they proposed an attention

mechanism in which spatial attention facilitates P activity which in turn inhibits M activity at the

same location. By using stimulus conditions favorable to P processing (i.e., reducing M

activity), thereby reducing the opportunity for P on M inhibition to occur, Yeshurun (2004)

found the decreased temporal resolution at the attended location was greatly reduced (e.g.,

isoluminant) or eliminated (e.g., red background).

Other attentional tasks, such as inhibition of return (IOR) and object-based attention,

have also been shown to be influenced by stimuli biased towards transient and sustained

channels (Brown, 2009; Brown & Guenther, in preparation; Brown, et al., under review;

Guenther, 2008; Guenther & Brown, under review). IOR has been shown to increase for stimuli

biased towards sustained channels compared to stimuli biased towards transient channels using

manipulations of stimulus spatial frequency (Brown, 2009; Brown & Guenther, in preparation)

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and abrupt vs. ramped stimulus presentation (Guenther, 2008; Guenther & Brown, under

review). Exploring the relationship between the object advantage (discussed below in greater

detail) and the M and P pathways, Brown et al (under review) ran an exogenous cuing task with

outline rectangles under equiluminant and non-equiluminant conditions. They hypothesized, due

to information processing differences between the M and P pathways, space- and object-based

attention systems may be more associated with the M and P pathways respectively. When

stimuli were presented at equiluminance (weakening the M response) the object advantage

disappeared. They argue the elimination of the object advantage was likely due to increased RTs

for shifts of attention within objects.

Object- and Space-Based Attention

One common and widely researched attentional effect is that of object-based attention.

One of the first methods for studying both object- and space-based mechanisms of visual

attention simultaneously, within the same paradigm, was developed by Egly, Driver, and Rafal

(1994). They used a spatial cuing paradigm in which two rectangular objects were presented on

the screen. In measuring space-based attention, one corner of an object was cued and then a

target could appear either at the cued end of the object or at the opposite end of the same object

and simple RT to target onset was measured. When the target appeared at the uncued end of the

same object space-based attention was measured because it only required attention to shift

between locations within the same object and not between two objects. When the target

appeared in the object that was not cued (in the location opposite of the cued location in the cued

object), an object-based component was added since attention must shift between two objects.

Differences in space- and object-based attention can be observed when RTs are compared for

9

within- and between- object shifts since the distance (in space) of the attentional shift is held

constant between the two conditions (Egly, Driver, & Rafal, 1994).

If this two rectangle display is modified to form a single object by joining two ends of the

rectangle (Iani, Nicoletti, Rubichi, & Umilta, 2001) then the object effect disappears. This

suggests the between-object effect observed in the two rectangle paradigm is not due to crossing

object borders, instead it reflects an attentional cost for shifting attention between two separate

objects (Iani, et al., 2001). Similarly, Brown, Breitmeyer, Leighty, and Denney (2006) tested

whether increasing the internal distance of objects over which attention is supposedly shifting

during within-object shifts could make within-object shifts as slow as between-object shifts.

They compared conditions with two rectangles, pairs of brackets, and pairs of arcs where the

internal distance was three times greater for the brackets and arcs. They found while there was

some increase in cost for shifting attention within the brackets and arcs (as compared to the

rectangles) the cost for shifting attention between two separate objects was still greater.

There are several major accounts for the apparent advantage for shifting attention within-

compared to between- objects including biased competition, attentional prioritization, and

spreading attention. Additionally, another account emphasizes the different processes involved

in an object based attention task and views the effect as a disadvantage for shifting attention

between two objects rather than an advantage for shifting within a single object.

Biased Competition

One account for the effects observed in object-based attention experiments uses the

notion of biased competition (Desimone, 1998; Desimone & Duncan, 1995). When applied to

object-based attention, it holds, the object advantage arises due to contributions from, and

competition between, both bottom-up (stimulus oriented) and top-down (goal oriented)

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information (Vecera, 2000; Vecera & Behrmann, 2001). Vecera (2000) argues for two general

types of competition between bottom-up biases in scenes with multiple objects. The first type of

competition involves regional segregation processes which result in one region becoming more

salient than the other (figure-ground segregation would be an example). The second type of

competition is between objects resulting in the selection of one over another. Top-down biases

are argued to relate to familiarity, in that familiar objects are selected by attention faster than less

familiar objects (Vecera & Farah, 1994). Additional top-down biases come from an observers

goals or expectations. It is the combination of these bottom-up and top-down biases which

compete to determine the perceptual organization of the visual scene and the allocation of

attention within it (Vecera, 2000).

Attentional Prioritization

The attentional prioritization account of object-based attention is based on the notion that

the attentional system prioritizes its search of space by taking into account probability

information (Shomstein & Behrmann, 2008; Shomstein & Yantis, 2002, 2004). Shomstein and

Yantis (2002) tested for object-based modulation of the flanker effect across five experiments.

The flanker effect occurs when incompatible items (flankers) near the target item interfere with

responses to the target while compatible flanker items do not interfere with the response to the

target and thus produce faster responses.

In their design, the target was either in the same object as the flankers or the target was in

a different object from the flankers. The spatial distance between the flankers and the target

(Experiments 2 and 3) as well as the appearance of and distance between the two objects

(Experiment 4) was varied. In the first four experiments space-based effects of the distractors on

the target were observed, but none of these manipulations revealed an object-based influence on

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the flanker effect (it did not matter whether the distractors were in the same or different objects).

In an additional experiment (Experiment 5) an uninformative cue was added to the sequence,

appearing before the test display, which would direct attention to one of the objects. Spatial

uncertainty was also added to the display, such that contrary to the first four experiments the

target could appear in multiple locations (in Experiments 1-4, the target always appeared in the

same location). With the addition of a cue and multiple target locations, object cuing was found

to influence the flanker effect. They argue, when attention was deployed to multiple locations in

the scene, spatial uncertainty occurs. This spatial uncertainty then facilitates the use of an

‘object-based attentional prioritization strategy’ in which locations within cued objects are

attended to before locations outside cued objects.

They later argue these results (Shomstein & Yantis, 2002) suggest an object-based

attentional prioritization strategy may occur when multiple locations in a scene require attention.

They refer to this strategy as configural and note it is context dependent and requires long-term

perceptual learning (Shomstein & Yantis, 2004). Attentional prioritization can be applied to

other object-based attention experiments such as Egly et al (1994). In a typical 2-bar experiment

like that of Egly et al (1994), the cued location has the highest probability of having a target

(typically around 60-75%). The two equidistant uncued locations then split the remaining

percentage of target locations; however, the uncued location within the cued object should be

influenced by the higher probability of the target appearing at the cued location in the same

object (even though the probability of it appearing there is not any greater that the uncued

location in the uncued object). This creates a scenario where the highest probability to find a

target is at the cued location, the next highest would be in the cued object, and then in the uncued

object. This pattern of probability matches with the way the data typically emerges (fastest RTs

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at the cued location, then the uncued location within the cued object, and the longest RTs at the

uncued location in the other object).

In order to distinguish between context (attentional priority) and configural (the objects),

Shomstein and Yantis (2004) manipulated the probability of targets appearing in specific

locations. At shorter SOAs they found effects of both context and configuration; however, at the

longer SOAs configural effects disappeared. Essentially, at longer SOAs only the probability

manipulation had an effect. From this they argue, object-based attention may involve at least

two different attentional mechanisms (Shomstein & Yantis, 2004). This suggests, while

attentional prioritization, may be an aspect of, or a contributing factor to, the object advantage, it

does not provide a complete account for the effect.

Spreading Attention

The spreading attention account of the object effect in object-based attention is based on

the notion that attention naturally spreads out from fixation. In the context of objects, it argues,

attention tends to spread out easier within the boundaries of an object than across the boundaries

of an object. In a two-bar object-based attention experiment, when an object is cued, attention

would spread out throughout the cued object providing an advantage for responses to uncued

targets within the cued object compared to targets in the uncued object.

A good example of data supporting the spreading of attention account is when Abrams

and Law (2000) tested participants judgments of temporal order of the appearance of two

simultaneous targets. Participants were shown a display with three disks which were set up to

form the corners of an equilateral triangle. Two of the disks were connected with a thick line

such that they had the appearance of a barbell. After one of the disks was cued (either

exogenously or endogenously) the targets would then appear simultaneously in the remaining

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two disks. The data revealed participants reported the target within the cued object as appearing

before the target in the uncued object.

An additional experiment (Abrams & Law, 2000: Experiment 7), using a two-bar design

tested whether the probability of a target appearing within the cued object could be leading to the

object advantage (attentional prioritization). They designed the experiment such that a target

would appear in the cued location 40% of the time, in the uncued location of the cued object

10% of the time, and in each uncued location of the uncued object 25% of the time. This created

a design in which the target was equally probable in both objects but the highest probability was

still at the cued location. Additionally, there was a higher probability for uncued targets to

appear in the uncued object than the cued object; however, typical object effects were still

observed.

Other studies have produced data that conflicts with a prioritization account. For

example, when items used in a flanker test were integral features of the objects in the display,

object based effects were observed (Richard, Lee, & Vecera, 2008). In their design, the target’s

location remained constant, as in the first experiments of Shomstein and Yantis (2002)

(described above). Attentional prioritization would not predict to find object-based differences

in this design (as in Shomstein and Yantis, 2002); however, by making the targets features

integral to the objects themselves (as opposed to separate items located on or within the objects)

object based effects were observed. They use this to argue for an integrality hypothesis which

considers the relationship between the objects and features/items used in object-based tasks.

When the task relevant features/ items are integral or a part of the objects structure then object-

based attention may be more likely to rely on an attentional spreading mechanism. When the

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task relevant items are not integral to the structure of the objects then object-based attention may

use an attentional prioritization mechanism (Richard, et al., 2008).

A Between-Object Disadvantage

While many of the studies of object-based attention focus on the object advantage (an

advantage for shifting attention within an object as compared to between two objects) others

have viewed this effect from the perspective of a disadvantage for shifting attention between two

objects as opposed to within a single object (Brown & Denney, 2007; Ho & Atchley, 2008; Iani,

et al., 2001). The importance of shifting attention for the generation of object-based effects has

been emphasized (Lamy & Egeth, 2002). Brown and Denney (2007) propose the effects could

be described through the three steps that would be associated with the task: engaging,

disengaging, and the shifting of attention. If one were to look at an object-based attention task,

the difference for between object shifts of attention as compared to within object shifts would be

the need to disengage attention from one object and then engaging to another object.

In order to determine the role of the engage, disengage, and shift operations in object-

based effects, Brown and Denney (2007) used conditions with two objects, one object, and no

objects in which attention shifted within an object, between two objects, between locations in

space (without objects), and between objects and locations outside of objects. The important

additions to the traditional two-bar paradigm were conditions in which attention shifted from

locations in space outside of an object into an object (isolating the effect of an object-based

engage operation) and when attention shifted from a location within an object to a location in

space outside of an object (isolating the effect of an object-based disengage operation).

They reported the typical effects observed in object-based attention experiments (using

the Egly et al., (1994) paradigm) when attention shifted between two objects as well as when it

15

shifted from an object to a location in space (no differences between these two conditions).

Additionally, no differences were observed between conditions when attention shifted between

two locations in space and when it shifted between locations within the same object (reporting

the typical within object effects). Interestingly, the cost was greater for shifts of attention from

an object to a location than when it shifted from a location to an object or between two locations.

The increased cost for conditions in which attention had to shift from an object to a location in

space (compared to shifting from a location in space into an object) and that this cost was no

different from that observed when shifting attention from one object to another (in the two-bar

conditions) illustrate the importance of the object-based disengage operation in object-based

effects.

Inhibition of Return

Another type of cuing task which has been explored from a transient and sustained dual-

channel perspective is inhibition of return (IOR). Research by Posner and Cohen (1984) has

shown, at longer stimulus onset asynchronies (SOAs), attention may be inhibited to return to

locations previously attended. This effect is manifest in shorter RTs for targets appearing at

uncued locations than targets appearing at the cued location. It was first termed reaction time

inhibition (RTI) and has been explored using a variety of stimuli and methods. This effect was

originally described as a sensory (Posner & Cohen, 1984) rather than an attentional phenomenon.

Although the attentional account (Posner, Rafal, Choate, & Vaughan, 1985) has been the focus

of most IOR research, recent studies have again highlighted the importance of sensory effects on

IOR (e.g., Bell, Fecteau, & Munoz, 2004; Brown, 2009; Brown & Guenther, in preparation;

Guenther, 2008; Guenther & Brown, under review; Reuter-Lorenz, Jha, & Rosenquist, 1996;

Sumner, 2006; Sumner, Nachev, Vora, Husain, & Kennard, 2004).

16

In order to explore the role of sensory influences on IOR some have manipulated relative

processing along the transient and sustained channels by manipulating stimulus conditions (e.g.,

Brown, 2009; Brown & Guenther, in preparation; Guenther, 2008; Guenther & Brown, under

review). Recently, Brown (2009) and Brown and Guenther (in preparation) demonstrated a

relationship between location IOR magnitude and transient and sustained channel activity

through manipulations of stimulus spatial frequency. IOR magnitude was less for low spatial

frequency stimuli expected to favor transient channels (a TC-bias) and greater for high spatial

frequency stimuli expected to favor sustained channels (a SC-bias). In order to ensure this

reported relationship observed between IOR magnitude and TC- and SC-biased conditions was

not specific to Gabor patch stimuli, Guenther (2008) and Guenther and Brown (under review)

used more traditional stimuli. Their stimuli consisted of simple luminance defined squares that

were presented either abruptly (simple on/off) or ramped (a gradual increase/decrease in

luminance). This type of manipulation has previously been used to generate TC- and SC-biased

conditions (e.g., Castiello, Badcock, & Bennett, 1999; Crewther, Kiely, & Crewther, 2006;

McAnany & Levine, 2005). Guenther and Brown (under review) found conditions with ramped

(SC-biased) targets produced greater IOR magnitudes than conditions with abrupt (TC-biased)

targets demonstrating convergent evidence with their findings using Gabor patches of greater

IOR to SC-biased stimuli.

Using the S/PP Paradigm to Study Visual Attention

There is a great deal of research on the attentional components of both the object

advantage and IOR (for IOR reviews, e.g., Berlucchi, 2006; Klein, 2000). The present

experiments aim to further explore the roles of the transient and sustained channels in visual

attention using these two well established attentional paradigms (known to produce strong and

17

consistent effects) while using a newer manipulation of transient and sustained channel

processing. Additionally, specific sensory influences on both of these effects have been

revealed by using TC- and SC-biased stimulus conditions. However, the major and prevalent

theoretical accounts of these attention effects do not sufficiently account for these sensory level

stimulus influences.

Brown et al (under review) demonstrated the object advantage can be influenced by

conditions biased towards the transient and sustained channels. When stimuli were presented as

psychophysically equiluminant with the background (compared to non-equiluminant conditions),

they found greater increases in RTs for within-object shifts of attention than between-object

shifts of attention. This resulted in the absence of an object advantage for equiluminant

conditions. This finding cannot be sufficiently explained by most of the current accounts of

object-based attention. For example, the biased attention (Desimone, 1998; Desimone &

Duncan, 1995) account holds that the object advantage is due to contributions from and

competition between stimulus and goal oriented information (e.g., Vecera, 2000; Vecera &

Behrmann, 2001; Vecera & Farah, 1994). In this account it is argued that more familiar objects

are selected faster than less familiar objects (Vecera & Farah, 1994). Other factors such as

stimulus saliency, and the observer’s goals and expectations are also argued to be important.

The stimuli used by Brown et al (under review), did not differ in any of these factors so this

account is not sufficient to address these data. Attentional prioritization (e.g., Shomstein &

Behrmann, 2008; Shomstein & Yantis, 2002, 2004) argues that attention uses probability

information to prioritize search. In Brown et al (under review), the probability information is

constant across conditions, so any differences observed cannot be attributed to differences in

prioritization strategies. The spreading attention account is based on the notion that attention

18

naturally spreads out from fixation and that it is easier for attention to spread within the

boundaries of a single object than between two separate objects. It is possible that

equiluminance could have reduced the ability of attention to spread; however, there were

differences in the effect of equiluminance on within- and between-object shifts of attention

which cannot be explained by the spreading attention account.

IOR has also been shown to be influenced by conditions biased towards the transient and

sustained channels (Brown, 2009; Brown & Guenther, in preparation; Guenther, 2008; Guenther

& Brown, under review). Guenther (2008) and Guenther and Brown (under review) used a

traditional IOR paradigm and compared stimuli presented abruptly or ramped on and off. They

found when stimuli were ramped (SC-biased) RTs at the cued location increased (the increase

was significantly larger for cued than uncued locations), leading to greater IOR. Additionally,

Brown (2009) and Brown and Guenther (in preparation) both found the same effect using high

(SC-biased) and low (TC-biased) spatial frequency Gabor patches as stimuli. When SC-biased,

high spatial frequency targets were used, RTs at cued locations were again increased greater than

RTs at uncued locations which resulted in greater IOR for high spatial frequency targets.

The S/PP paradigm (Leonova, et al., 2003; Pokorny & Smith, 1997; Smith & Pokorny,

2003) is a simple manipulation of transient and sustained channel processing which has been

shown to be effective; however, it has not been used with an RT measure in the context of a

typical cuing experiment. As a tool for creating conditions with relative TC- and SC-biases, the

S/PP paradigm is very simple to apply and use and could thus be a valuable addition to the

currently used methods for generating TC- and SC-biased conditions in attention research. Four

experiments were designed to test whether the S/PP paradigm can be used with an RT measure

and how it influences the deployment of attention in two commonly used attention tasks. The

19

first experiment tested the effectiveness of the S/PP paradigm with a RT measure producing a

pattern of RT data consistent with what would be expected from a manipulation of processing

along transient and sustained channels. Experiments 2 and 3 tested both the effect of the S/PP

paradigm on an object-based attention task and what about the pulse of the pedestal is important

(i.e., is it the pulse of the pedestal that is important or just having a large transient luminance

event which over stimulates transient channels). A fourth experiment used the S/PP paradigm in

an IOR task with traditional IOR stimuli and conditions similar to those used by Guenther (2008)

and Guenther and Brown (under review).

It is also important to consider the nature of the S/PP paradigm as a manipulation of

transient and sustained channel processing. Manipulations of stimulus spatial frequency,

cue/target presentation, and even equiluminance are manipulations that are primarily related to

the presentation of the stimuli themselves (e.g., Brown, 2009; Brown & Guenther, in preparation;

Brown, et al., under review; Guenther, 2008; Guenther & Brown, under review) and can be

described as being relevant to the task. However, the S/PP paradigm uses the presence of a large

transient event occurring in the background, which can be described as irrelevant to the task, to

manipulate transient and sustained channel processing. It is possible this difference in the nature

of these manipulations could lead to differences in how they influence performance in attention

tasks.

20

CHAPTER 2

EXPERIMENT 1

The first experiment tested whether the S/PP paradigm can be used with a RT measure.

The S/PP paradigm has been shown to be an effective method for generating conditions biased

towards transient and sustained channels for contrast sensitivity measures (Leonova, et al., 2003;

Pokorny & Smith, 1997; Smith & Pokorny, 2003) but it has not been used with a RT measure (to

the authors knowledge). To achieve this, cues and targets appeared at center screen (no shifting

of attention necessary) and RTs were measured to the target presented at center screen. Previous

work (e.g., Breitmeyer, 1975) comparing RTs to conditions reflecting biases between transient

and sustained channels indicate that SC-biased conditions should result in longer RTs than TC-

biased conditions. Additionally, a defining characteristic of the transient and sustained channels

is the speed of their response to stimuli. Transient channels are characterized by a faster

‘transient’ response while sustained channels are characterized by a slower, tonic ‘sustained’

response. Therefore, stimulus conditions that would relatively bias processing towards sustained

channels would be expected to produced slower RTs than stimulus conditions biased towards

transient channels. If the S/PP paradigm is effective with a RT measure then, at a minimum, the

data should reflect this pattern, producing results in which RTs are longer for the SC-biased

pulsed pedestal condition than the TC-biased steady pedestal condition.

21

Method

Participants

An a priori power analysis was conducted using G*Power 3 software (Faul, Erdfelder,

Lang, & Buchner, 2007) using an expected effect size, 22η = .293, calculated by averaging the

post hoc effect sizes reported by Guenther and Brown (under review) comparing the effect of

abrupt (TC-biased) and ramped (SC-biased) stimulus conditions on IOR. The power analysis

revealed a necessary sample size of 8. 18 (11 female) participants participated for course credit.

All participants had normal or corrected to normal vision and were classified as right handed

according to the Annett Handedness Scale.

Stimuli and Apparatus

Stimuli were presented and data collected using E-Prime software running on a PC

computer using a color monitor running at 85 Hz. Responses were collected from a standard

QWERTY keyboard. Participants sat in a darkened room 191.8 cm from the monitor using a chin

rest.

Cues were an outline square shaped object subtending 0.8°, presented at center screen,

defined by a 0.03° thick line. Targets were a solid square shaped object subtending 0.6°. The

pedestal (when present) was a 12.58° square centered around fixation. The luminance of the

stimuli (objects, fixation, cues, and targets) was 13.2 cd/m2. Background luminance depended

on the specific pedestal condition used. In the bright pedestal condition the background was be

3.1 cd/m2 and the pedestal was 49.9 cd/m2. For the dark pedestal condition the luminance of the

background and pedestal was reversed resulting in a background luminance of 49.9 cd/m2 and a

pedestal luminance of 3.1cd/m2.

22

Procedure

The task was a go/no-go task with simple RT measured to target onset. Targets appeared

on 80% of trials. Each trial began begin with a fixation “x” presented at center screen. After a

keypress, the fixation “x” remained at center screen for 1000 ms, followed by a 50 ms cue, a 150

ms inter-stimulus interval (ISI), then the target appeared for 1500 ms or until a response was

made. On steady pedestal conditions the objects were presented on top of the pedestal which

appeared after the keypress starting the trial. For pulsed pedestal conditions the pedestal

appeared with the onset of the target. RTs were measured from the onset of the target until a

response is made. Participants received an error message for RTs less than 150 ms or if a false

alarm was made.

Bright and dark pedestal conditions as well as steady and pulsed pedestal conditions were

run within-subjects and randomized. The experiment was run in a single block of 100 trials

(excluding 10 practice trials before the start of the experiment) resulting in 20 trials per within-

subject condition. Participants were instructed to refrain from making a response on catch trials

(20%).

Results and Discussion

Prior to data analysis, participants were excluded using a two-stage process. The first

stage excluded 2 participants due to excessive false alarms (20% and above) leaving a mean false

alarm percentage of 5%. Trials with RTs outside the range of 175-1500 ms were excluded before

the second stage. In the second stage one participant was excluded because of mean RTs

exceeding 2.5 standard deviations above the mean. The resulting number of participants was 15

(9 female).

23

RT data were submitted to a 2 (steady vs. pulsed pedestal) x 2 (pedestal direction: bright

vs. dark) repeated measures ANOVA. The RT data are consistent with TC- and SC-biased

conditions with greater RTs to the pulsed (SC-biased) condition (403 ms) than the steady (TC-

biased) condition (367 ms) F(1,14) = 50.15, 22η = .78, p < .05 (see Figure 5). Importantly, neither

the main effect of pedestal direction, nor the interaction between the pedestal effect and direction

were significant p >.05. The data suggest the S/PP paradigm may be effective in experiments

with a RT measure. Additionally, the similarity in responses between bright and dark pedestals

provides evidence against the argument that RT differences between steady- and pulsed-pedestal

conditions resulted from brightness masking.

24

CHAPTER 3

EXPERIMENT 2

The RT data from Experiment 1 are consistent with the expected pattern of results from

two conditions differing in relative transient and sustained channel processing. Previous

research exploring the role of transient and sustained channels in the object advantage have

found that it can be eliminated at equiluminance (Brown, et al., under review). To further

examine the relationship between transient and sustained channels and the object advantage, RT

data were collected in a two-rectangle (e.g., Egly, et al., 1994) paradigm with a S/PP

manipulation. The abrupt onset of the target in the steady-pedestal condition would be expected

to generate a strong transient response and reflect a condition biased towards transient channels.

In the pulsed-pedestal condition, the onset of the pedestal (with the target) would over stimulate

the transient channels forcing the sustained channels to take a larger role in the processing of the

target stimulus. Thus the pulsed-pedestal condition is argued to reflect a condition relatively

biased towards sustained channels. Any differences observed in the pattern of results between

these two conditions can be argued to be reflective of the role of transient and sustained channels

in the task.

The steady-pedestal condition should produce effects replicating the typical object-based

cuing effect with the fastest reaction times (RT) to validly cued target locations, slower RTs to

the invalidly cued locations within the same object, and the slowest RTs to the invalidly cued

locations in the uncued object. If the pulsed-pedestal condition is effective at generating a SC-

bias then the overall RTs should be longer than the steady pedestal condition (as observed in

25

Experiment 1). Additionally, for it to be an effective manipulation in an object-based attention

paradigm, a validity effect should also be present with the fastest RTs to the cued location and

longer RTs to uncued locations.

When Brown and colleagues (under review) used stimuli presented at psychophysical

equiluminance, they found RTs to within-object shifts of attention were increased relative to

between-object shifts of attention. This increased effect on within-object shifts of attention led

to the elimination of the object advantage. Similar to a manipulation of equiluminance, the

pulsed-pedestal condition is argued to reflect a SC-bias. If the pulsed-pedestal condition has a

similar effect then a pattern of results in which RTs are increased to within-object shifts of

attention should be observed.

However, unlike the manipulation of equiluminance, the S/PP paradigm is entirely task-

irrelevant. It is slightly different (although in an important way) from many of the other

manipulations of TC and SC processing used to study IOR and the object advantage.

Specifically, the manipulations used to study IOR (e.g., Brown, 2009; Brown & Guenther, in

preparation; Guenther, 2008; Guenther & Brown, under review) have been specific to the stimuli

participants were instructed to respond to. In Brown (2009) and Brown and Guenther (in

preparation) conditions biased towards transient and sustained channels were created by

manipulating the spatial frequency of the cues and targets. Guenther (2008) and Guenther and

Brown (under review) manipulated the temporal nature of the cues and targets

appearance/disappearance. Brown et al (under review) used a manipulation of psychophysically

determined equiluminance. The S/PP pedestal paradigm does not manipulate the cues and

targets directly; instead conditions biased towards transient and sustained channels are generated

through a manipulation of the background which drives the overall MC/TC response towards

26

saturation. It is therefore possible the S/PP manipulation may influence the results in IOR and

object-based attention experiments differently than manipulations of the cues/targets.

Method

Participants

As in Experiment 1, an a priori power analysis was conducted using G*Power 3 software

(Faul, et al., 2007) using an expected effect size, 22η = .293, calculated by averaging the post hoc

effect sizes reported by Guenther and Brown (under review) comparing the effect of abrupt and

ramped conditions on IOR. The power analysis revealed a necessary sample size of 8 (for each

between-subjects condition). Fifty-one (26 female) participants participated for course credit.

All participants had normal or corrected to normal vision and were classified as right handed

according to the Annett Handedness Scale


Stimulus presentation was conducted using SuperLab 4.0 on a PC computer using a color

CRT monitor running at 85Hz. Responses were collected from a seven button response box.

Participants sat in a darkened room 68.6 cm from the monitor using a chin rest.

The objects consisted of two 5.33° x 0.67° outline rectangles defined by a 0.17° thick line

tilted ±45° from a vertical orientation. They were centered 2.34° from fixation which consisted

of a 0.59° “x” defined by a 0.01° line. Targets consisted of a 0.33° square that filled in one

corner of the objects and cues consisted of a slight (0.17°) enlarging of one of the rectangle

edges. The pedestal (when present) was a 12.58° square centered around fixation. The

luminance of the stimuli (objects, fixation, cues, and targets) was 13.2 cd/m2. Background

luminance depended on the specific pedestal condition used. In the bright pedestal condition the

background was 3.1 cd/m2 and the pedestal was 49.9 cd/m2. For the dark pedestal condition the

27

luminance of the background and pedestal were reversed resulting in a background luminance of

49.9 cd/m2 and a pedestal luminance of 3.1cd/m2.

Procedure

The bright and dark pedestal conditions were run between-subjects while all other

conditions were within-subjects. Each group was presented both steady- and pulsed-pedestal

conditions (for one luminance condition) randomly intermixed within each block of the

experiment. The experiment was run in 4 blocks of 160 trials for a total of 640 trials (excluding

10 practice trials before the start of the experiment). Each block of trials contained 20% catch

trials in which participants were instructed to refrain from making a response. Of the remaining

trials 75% were valid trials in which the cue and target appeared in the same location. The

remaining 25% of the trials were invalid trials in which the cue and target did not appear in the

same location. On half of these trials the target appeared in the opposite end of the same object

(invalid within) and on the other half the target appeared in the nearest end of the uncued object

(invalid between) such that the distance of shift was constant for both within- and between-

object conditions.

Each trial (see Figure 2) began with a fixation “x” presented at center screen. After a

keypress the objects appeared at center screen for 1000 ms, followed by a 50 ms cue, a 150 ms

ISI, then the target appeared for 1500 ms or until a response was made. On steady-pedestal

conditions the objects were presented on top of the pedestal which appeared after the keypress

starting the trial. For pulsed-pedestal conditions the pedestal appeared with the onset of the

target. Reaction times (RTs) were measured from the onset of the target until a response is

made. Participants received an error message for RTs less than 150 ms or if a false alarm was

made.

28


Prior to data analysis, participants were excluded using the same two-stage process as

described in Experiment 1. The first stage excluded 10 participants (4 in the bright condition)

due to excessive false alarms (18% and above) leaving a mean false alarm percentage of 9%. In

the second stage 2 participants were excluded (1 in the bright condition). The resulting number

of participants was 39 (19 female) leaving 20 (12 female) in the bright condition and 19 (7

female) in the dark condition.

RT data were submitted to a 2 (steady vs. pulsed pedestal) x 2 (cue validity: valid vs.

invalid) x 2 (pedestal direction: bright vs. dark) mixed ANOVA with pedestal direction as a

between-subjects factor. The main effect of pedestal direction was not significant F(1,37) =

2.33, 22η = .06, p > .13 nor did it result in any significant interactions with any other factors.

Therefore, the data are presented collapsed across pedestal direction. This finding supports the

position from Experiment 1 against brightness masking as the cause of the differences between

steady- and pulsed-pedestal conditions. The RT data are consistent with what would be expected

from conditions biased towards transient and sustained channels with greater RTs to the pulsed

(SC-biased) condition (440 ms) than the steady (TC-biased) condition (368 ms) F(1,37) =

440.53, 22η = .92, p < .05.

RTs were faster for valid (383 ms) than invalid (425 ms) trials F(1,37) = 188.16, 22η =

.84, p < .05 indicating the presence of a cuing effect. The S/PP manipulation influenced the

cuing effect F(1,37) = 15.56, 22η = .30, p < .05 such that the pulsed condition had a greater

influence (a 14 ms increase) on invalid than valid RTs t(38) = 3.99, p < .05 (paired-samples t-

test). The presence of the object advantage was confirmed (see Figure 6) through paired-samples

29

comparisons for both steady- (26 ms) t(38) = 7.36, p < .05 and pulsed-pedestal (23 ms)

conditions t(38) = 4.90, p < .05.

Of greatest importance, the standard cuing effect was present in both steady- and pulsed-

pedestal conditions indicating the cue was effective at attracting attention. As predicted, the

steady-pedestal condition produced the typical pattern of effects (i.e., a cuing effect and the

presence of the object advantage). Unlike Brown et al (under review) the condition biased

towards sustained channels did not eliminate the object advantage. However, the S/PP paradigm

still revealed an influence of transient and sustained channels in an object-based attention task.

The pulsed-pedestal condition had a greater influence on RTs in trials in which the target

location was invalidly cued (see Figure 7). It has been argued that the M system serves as a

guidance system in visual attention (e.g., Cheng, et al., 2004; Vidyasagar, 1999; Vidyasagar &

Pammer, 1999). Illustrating this, Cheng et al (2004) compared performance in feature and serial

search tasks under equiluminant and non-equiluminant conditions. As target detection in a

feature search task would require less attentional resources than target detection in a serial search

task (e.g., Treisman & Gelade, 1980), Cheng et al (2004) did not find differences in the RT to

targets in a feature search task. However, performance at equiluminance in the serial search task

was significantly impaired when compared to performance when luminance contrast was present.

In the context of the present experiment, the pulse of the pedestal may have reduced the ability of

the M system (i.e., transient channels) to guide attention as with the equiluminant condition of

Cheng et al (2004). This then resulted in a greater increase in the time to respond to targets

requiring a shift of attention. Additionally, the pattern of results suggest task-relevant and task-

irrelevant manipulations of TC and SC processing will affect attention differently.

30

CHAPTER 4

EXPERIMENT 3

Comparisons between bright and dark pedestal conditions in Experiments 1 and 2 provide

an argument against brightness masking; however, there is another alternative account for

Experiment 2 that needs to be addressed. It is possible that the large transient event occurring

with (and at the same location as) the stimuli could influence RTs. For example, the pulse could

simply make it more difficult to see the stimuli and thereby respond to the target? If this were

the case, then it would be expected to appear as a constant added to the data from Experiment 2

(i.e., the effect on RTs would be the same for valid and invalid conditions). That the data did not

reflect this, can be used as an argument against this account. To further rule out brightness

masking or a difficulty in responding to the target due to the pedestal, a pulse of the background

instead of the central region was used in this experiment.

It can be argued that the steady/pulsed pedestal paradigm results in conditions biased

towards the transient and sustained channels due to a large transient event occurring with, but

irrelevant to, the onset of a target. If this is the case then similar results should be observed if the

paradigm is modified such that the transient event occurs outside the region of interest. If this

conceptualization of the S/PP paradigm is accurate, and if the effects are not due to masking,

then it should replicate the results of Experiment 2. However, if the results obtained from

Experiment 2 are due to other factors such as masking or a difficulty in perceiving and

responding to the target, then a background pulse should produce similar results to the steady-

pedestal condition.

31

Method

Participants

An a priori power analysis was conducted using G*Power 3 software (Faul, et al., 2007)

using an expected effect size, 22η = .30, calculated by using the post hoc effect size from

Experiment 2 comparing the effect of the S/PP manipulation on the object advantage. The power

analysis revealed a necessary sample size of 14 (for each between-subjects condition). 61 (41

female) participants participated for course credit. Participant information and requirements is

the same as in Experiments 1 and 2.


Same as in Experiment 2 (except see Figure 8).

Procedure

The procedure was the same as in Experiment 2 with the following exception. The

luminance change in the pulsed pedestal condition occured in the background (see Figure 8).

This change reversed the luminance in the target region for the bright and dark conditions since

the changes will occur in the background region. Additionally, this change resulted in the central

region (where the objects and stimuli appear) remaining constant throughout each trial for both

steady- and pulsed-pedestal conditions.


Prior to data analysis, participants were excluded using the same two-stage process as

previously described. The first stage excluded 7 participants (4 from the bright pedestal

condition) due to excessive false alarms (18% and above) leaving a mean false alarm percentage

of 8%. In the second stage 2 participants were excluded (1 from the bright pedestal condition).

32

The resulting number of participants was 52 (32 female) leaving 19 (13 female) in the bright

condition and 33 (19 female) in the dark condition.

RT data were submitted to a 2 (steady vs. pulsed ) x 2 (cue validity: valid vs. invalid) x 2

(pedestal direction: bright vs. dark) mixed ANOVA with pedestal direction as a between-

subjects factor. The main effect of pedestal direction was not significant F(1,50) = 0.49, 22η =

.01, p > .48. Pedestal direction did interact with the overall RT effect of the pulsed condition

F(1,50) = 17.56, 22η = .26, p < .05 such that there was a greater overall RT effect of the pulse in

the bright condition (50 ms) than in the dark condition (22 ms) t(50) = 4.49, p < .05. Since the

pedestal direction factor did not interact with the validity or S/PP factors (the primary factors of

interest) or the interaction between the two, the data are presented collapsed across pedestal

direction.

As in Experiment 2, the overall RT data are consistent with what would be expected from

TC- and a SC-biased conditions with greater RTs to the pulsed (SC-biased) condition (390 ms)

than the steady (TC-biased) condition (354 ms) F(1,50) = 134.50, 22η = .73, p < .05. RTs were

faster for valid (351 ms) than invalid (393 ms) trials F(1,50) = 197.60, 22η = .80, p < .05

indicating the presence of a cuing effect. As in Experiment 2, the S/PP manipulation influenced

the cuing effect F(1,50) = 20.75, 22η = .29, p < .05 such that the pulsed condition had a greater

(15 ms) influence on invalid than valid RTs t(51) = 4.90, p < .05 (paired-samples t-test) (see

Figure 9). The presence of the object advantage was confirmed (see Figure 10) through paired-

samples comparisons for both steady- (22 ms) t(51) = 8.19, p < .05 and pulsed (30 ms)

conditions t(51) = 8.68, p < .05.

As in Experiment 2, the cue was effective in both steady and pulsed conditions indicating

the cue effectively captured attention. The effect of the S/PP paradigm on RTs was similar to the

33

previous results such that the pulsed condition had a greater influence on invalid RTs (see Figure

9).

To compare the data from Experiments 2 and 3, they were submitted to a 2 (steady vs.

pulsed) x 2 (cue validity: valid vs. invalid) x 2 (Experiment 1 vs. Experiment 2) mixed ANOVA

with experiment as a between-subjects factor. The data revealed a small (33 ms) overall RT

difference between Experiments 2 and 3 F(1,89) = 7.62, 22η = .08, p < .05. The effect of the

pulsed condition on overall RTs was greater in Experiment 2 (72 ms) than Experiment 3 (33 ms)

F(1,89) = 62.45, 22η = .41, p < .05. However, experiment did not interact with the validity factor

or with the interaction of the pedestal and validity. The greater effect of the pulsed-pedestal

condition on overall RTs in Experiment 2 suggest that pulsing the same region in space in which

the stimuli of interest appear may decrease the participants’ ability to perceive and respond to the

target. However, due to the similarity between Experiments 2 and 3 in regards to the validity of

the cue and the effect the pulsed-pedestal condition had on validity, it can be argued that any

potential difficulty in perceiving and responding to a target created by localizing the pulse and

target in the same region of space is not responsible for the pattern of results observed in

Experiment 2.

34

CHAPTER 5

EXPERIMENT 4

Experiments 2 and 3 used the S/PP paradigm to explore the contributions of transient and

sustained channels in an object-based attention task. Another cuing task which has been

explored from a transient and sustained dual-channel perspective is IOR. Previous data has

suggested SC-biased conditions are associated with greater IOR magnitudes than TC-biased

conditions (e.g., Brown, et al., 2006; Brown & Guenther, in preparation; Guenther, 2008;

Guenther & Brown, under review). For example, Guenther and Brown (under review) used

abrupt (TC-biased) and ramped (SC-biased) stimulus presentations to manipulate TC and SC

processing in an IOR task and found greater IOR when targets were ramped than when they were

presented abruptly. These stimulus manipulations (target spatial frequency and target ramping)

were task-relevant manipulations of the specific stimuli used. As mentioned above, the S/PP

paradigm is task-irrelevant, and in Experiments 2 and 3 it has influenced performance in an

object-based attention task differently than previous research using task-relevant equiluminant

conditions. Research exploring the role of transient and sustained channels in IOR have used

multiple stimulus manipulations producing similar results with SC-biased stimuli producing

greater IOR (Brown, et al., 2006; Brown & Guenther, in preparation; Guenther, 2008; Guenther

& Brown, under review). Therefore, the S/PP paradigm was run in an IOR task to test whether it

would replicate previous findings (Brown, et al., 2006; Brown & Guenther, in preparation;

Guenther, 2008; Guenther & Brown, under review) or continue to operate differently than task-

relevant manipulations.

35

The data from Experiments 2 and 3 suggest the S/PP paradigm operates differently than

task-relevant stimulus manipulations. In both experiments the pulsed condition had a

significantly greater effect on targets that were presented in invalidly cued locations. IOR is an

effect that results from increased RTs at validly cued relative to invalidly cued locations. If the

S/PP paradigm is consistent in its influence on attention, then it should produce a similar pattern

of results in the IOR task (greater increase for invalidly cued RTs). However, unlike SC-biased

conditions which led to greater IOR magnitudes through greater effects at the validly cued

location (Brown, et al., 2006; Brown & Guenther, in preparation; Guenther, 2008; Guenther &

Brown, under review), The pulsed pedestal condition would be expected to have a greater effect

at the invalidly cued location thereby reducing IOR.

Method

Participants

An a priori power analysis was conducted using G*Power 3 software (Faul, et al., 2007)

using an expected effect size, 22η = .293, calculated by averaging the post hoc effect sizes

reported by Guenther and Brown (under review) comparing the effect of abrupt vs. ramped

stimulus manipulation on location-based IOR. The power analysis revealed a necessary sample

size of 8. 45 (41 female) undergraduates participated in this experiment for course credit.

Participant information and requirements is the same as in Experiments 1-3.


The stimuli and apparatus were the same as in Experiment 1 with the following

exceptions.

Cues and targets are square shapes subtending 0.4° and 0.6° respectively and were

centered 2.1° from the fixation point which consisted of a 0.1° dot presented at center screen. As

36

in Experiment 1 (but unlike Experiments 2 and 3) Participants sat 191.8 cm from the monitor

using a chin rest.

Procedure

The procedure was the same as in Experiment 1 with the following exceptions.

Bright and dark luminance pedestal conditions were counterbalanced as a within-subjects

variable in two separate blocks of trials. Each block consisted of 10 practice trials followed by

200 randomly presented experimental trials. There was a short break between blocks. The

within-subjects factors created a design generating 8 conditions, each receiving 20 trials. Forty

catch trials (20%), in which no target is presented, were included.

The specific cue duration and stimulus onset asynchrony (SOA) was the same as those

used in Guenther & Brown (under review). Each trial (see Figure 11) began with a keypress

after the participant directed their gaze at the fixation stimulus in the center of the screen. One

second after starting the trial, a cue appeared for 600 ms. The stimulus onset asynchrony (SOA)

was 800 ms with an ISI of 200 ms. The target then appeared and the participant responded by

pressing the ‘0/Ins’ key on the keyboard with their right index finger. A blank gray screen was

then presented for 750 ms between trials and the return of the fixation stimulus signaled the next

trial is ready to begin. If a participant responded during a catch trial an error message was

presented at center screen.


Twenty-two participants (48%) were excluded from data analysis due to excessive false

alarms (20% and above) on one or both blocks of trials (see Appendix A). 2 participants were

excluded due to means greater than 2.5 standard deviations of the mean, leaving a total of 21 (18

female) participants. The mean false alarm rate was 10%.

37

The RT data were submitted to a 2 (pedestal direction: bright vs. dark) x 2 (pedestal:

steady vs. pulsed) x 2 (validity: valid vs. invalid) repeated measures ANOVA. As in

Experiments 1-3, overall RTs were greater to pulsed- (369 ms) than steady-pedestal (329 ms)

conditions F(1,20) = 119.34, 22η = .86, p < .05. As in Experiment 3, overall RTs between bright

and dark pedestal conditions were different F(1,20) = 7.63, 22η = .28, p < .05, however, in this

case, overall RTs were greater (20 ms) for the dark compared to bright pedestal condition.

Additionally, as in Experiment 3, the pedestal direction did interact with overall pedestal RT

effects F(1,20) = 5.40, 22η = .21, p < .05. Again, this effect was in the opposite direction as

Experiment 3 such that the pulsed-pedestal had a greater effect in the dark (47ms) compared to

bright (33 ms) condition. Importantly, these RT effects of pedestal direction, did not influence

the effects of interest, namely IOR or its interaction with the pedestal condition.

As in Experiment 3, the effects of pedestal direction did not influence the main effect of

cue validity or its interaction with pedestal condition so those data are presented collapsed across

pedestal direction. Indicative of an overall IOR effect (see Figure 12), overall RTs were slower

at the valid location (365 ms) than at the invalid location (333 ms) F(1,20) = 90.61, 22η = .82, p <

.05. IOR was observed for both steady (43 ms) t(20) = 9.20, p < .05 and pulsed (22 ms) t(20) =

6.24, p < .05 conditions. Consistent with Experiments 2 and 3, the pedestal condition interacted

with cue validity F(1,20) = 19.34, 22η = .49, p < .05. The effect of the pulse was significant for

both valid (30 ms) t(20) = 5.76, p < .05 and invalid (50 ms) t(20) = 15.15, p < .05 trials;

however, the pulse had a 20 ms greater effect on RTs to invalidly than validly cued trials t(20) =

4.40, p < .05 (see Figure 13). The result of the increased RTs to invalid trials due to the pulsed-

pedestal condition is a significant reduction in IOR magnitude for pulsed- compared to steady-

pedestal conditions t(20) = 4.40, p < .05.

38

By using an IOR task, the data were able to confirm the S/PP paradigm acts differently in

attention tasks than previous task-relevant manipulations (e.g., Brown, 2009; Brown & Guenther,

in preparation; Guenther, 2008; Guenther & Brown, under review). The data were consistent

across all three experiments. The pulse condition, whether it occurred outside of or within the

same region of space in which the target stimuli appeared, and across two different attention

tasks, leads to greater increases in RTs to targets appearing in invalidly cued locations compared

to targets appearing in validly cued locations. As predicted this difference in the nature of the

S/PP manipulation increased the RTs at the invalidly cued location in the IOR task thus resulting

in a significant reduction in IOR magnitude in the pulsed condition.

39

CHAPTER 6

GENERAL DISCUSSION

The S/PP paradigm is an established sensory manipulation that has been used to test for

M and P functionality in a variety of clinical populations. It has been used in populations with

retinitis pigmentosa (Alexander, et al., 2003; Alexander, et al., 2004; Alexander, et al., 2001;

Alexander, et al., 2005), anisometric amblyopia (Zele, et al., 2007), migraines (McKendrick &

Badcock, 2003), and schizophrenia (Delord, et al., 2006). Other uses have been to explore M

and P contributions to vertical anisotropies in the visual field (McAnany & Levine, 2007) as

well as their contributions to some visual illusions (McAnany & Levine, 2005; Puts, et al., 2005).

One area in which this paradigm had not been tested was in studies using RT as a measure. The

data from the present experiments suggest the S/PP paradigm can be effectively used with a RT

measure. These data indicate the S/PP paradigm may be a valuable tool in exploring the role of

transient and sustained channels in visual attention.

The first experiment demonstrated the RT data obtained from conditions using a S/PP

manipulation are consistent with what would be expected from a manipulation of TC and SC

processing. Due to the latency differences between transient and sustained responses, conditions

reflecting a TC-bias were expected to produce faster RTs than conditions reflecting a SC-bias

(e.g., Breitmeyer, 1975). In the S/PP paradigm, steady-pedestal conditions are thought to reflect

a TC-bias while pulsed-pedestal conditions are thought to reflect a SC-bias (e.g., Leonova, et al.,

2003; Pokorny & Smith, 1997; Smith & Pokorny, 2003). Using a simple RT response to targets

presented at center screen, the data from Experiment 1 revealed longer RTs for the SC-biased

40

pulsed-pedestal condition. Although, this difference in RTs between steady- and pulsed-pedestal

conditions does not, in itself, confirm TC- and SC-biased conditions, these data are consistent

with the expected pattern of results that would result from a manipulation of TC- and SC-

processing. This, taken with the previous use of the S/PP paradigm to generate M- and P-biased

conditions (e.g., Alexander, et al., 2003; Alexander, et al., 2004; Alexander, et al., 2001;

Alexander, et al., 2005; Leonova, et al., 2003; McAnany & Levine, 2005, 2007; McKendrick &

Badcock, 2003; Pokorny & Smith, 1997; Smith & Pokorny, 2003; Zele, et al., 2007) allows for

the argument that the S/PP paradigm is effective at producing TC-and SC-biased conditions and

that the effect of this manipulation can be observed with a RT measure.

While the S/PP paradigm may be effective with a RT measure (as Experiment 1

suggests), it is possible the luminance change occurring with the target in the pulsed condition

could reduce the visibility of, and the ability to respond to, the target. Additionally, it was

possible brightness masking could have been contributing to the observed results. Two measures

were taken to address these issues. First, in all four experiments pedestal conditions included a

luminance change that was either a luminance increment or decrement. The data from

Experiments 1 and 2 revealed no differences in responses to conditions in which the pedestal was

either a luminance increment or decrement providing evidence that brightness masking was not a

factor in the results. While there were some overall RT differences between bright and dark

pedestals in Experiments 3 and 4, these overall RT differences did not interact with the attention

effects. Specifically, the effect of the pedestal on RTs at cued and uncued locations was not

different for bright and dark pedestal conditions.

To further ensure the luminance change was not causing brightness masking or making it

more difficult to perceive and respond to the target, Experiment 3 removed the pulse from the

41

target region. In looking at overall RTs, there was a greater effect of the pulsed condition on

overall RTs in Experiment 2 when compared to Experiment 3. This does suggest pulsing the

same region in space in which the stimuli of interest appear may decrease the participants’ ability

to perceive and respond to the target. Furthermore, the effect of the pulse on RTs to targets

appearing at validly cued locations is similar in Experiments 1, 3, and 4. It is likely this

increased difficulty in perceiving the target (with a central pulse), combined with the small size

of the target (0.33°) used in Experiment 2 led to the overall greater pulse effect observed in

Experiment 2. Future experiments should test this by replicating Experiment 1 with a smaller

target. However, due to the similarity between Experiments 2 and 3 in regards to the validity of

the cue and the effect of the pulsed condition on validity (i.e., the increased RT at invalidly cued

locations due to the pulse is similar in Experiments 2-4), it can be argued that this potential

difficulty is not responsible for the pattern of results observed in Experiment 2. In other words,

when the pulse occurs in the same region of space as the target, it may result in an overall

slowing of the response to the target. This is manifest as a constant added to the RT data;

however, the addition of this constant does not influence or interact with the cuing effect or the

influence of the S/PP paradigm on the cuing effect.

Previous work looking at the relationship between the object advantage and TC- and SC-

processing (Brown, et al., under review) demonstrated the object advantage can be influenced by

TC- and SC-biased conditions. When stimuli were presented at equiluminance the object

advantage was eliminated. In the present experiments (Experiments 2 and 3) the S/PP paradigm

did not influence the object advantage. The data from these experiments revealed the standard

cuing effect in both steady and pulsed conditions, which is important because it indicates the

cues in both steady and pulsed conditions were effective at attracting attention. The steady

42

conditions were predicted to produce the typical pattern of effects (i.e., a cuing effect and the

presence of the object advantage) (e.g., Egly, et al., 1994). If the SC-biased pulsed conditions

had a similar effect on attention as a manipulation of equiluminance then the data were expected

to replicate Brown et al (under review) thus eliminating the object advantage; however, this was

not the case.

Although both the pulsed conditions and equiluminance (as well as manipulations of

spatial frequency and stimulus ramping) are thought to reflect conditions with a SC-bias there is

one important difference between these manipulations. Previous experiments exploring the role

of transient and sustained channels in visual attention (e.g., Brown, 2009; Brown & Guenther, in

preparation; Brown, et al., under review; Guenther, 2008; Guenther & Brown, under review)

used stimulus manipulations that were task-relevant. Describing these manipulations

(equiluminance, stimulus spatial frequency, and stimulus ramping) as task-relevant means they

were manipulations of the cues and targets used in the attention task. The S/PP paradigm is a

task-irrelevant manipulation in that it does not change the cues and targets used in the task,

instead it is a manipulation occurring entirely in the background. Due to this difference, it was

hypothesized the S/PP manipulation may have a different effect on visual attention than

previously reported task-relevant manipulations.

Supporting the hypothesis that the nature of the manipulation (task-relevant or irrelevant)

may influence the effect of TC- and SC-biased conditions on visual attention, unlike the task-

relevant manipulation of equiluminance (Brown, et al., under review), the task-irrelevant SC-

biased pulsed conditions did not eliminate the object advantage. However, the S/PP paradigm

still revealed an influence of transient and sustained channels in an object-based attention task.

The pulsed conditions had a greater influence on RTs in trials in which the target location was

43

invalidly cued. The greater effect on RTs at invalidly cued locations revealed while the pulsed

conditions led to a general increase in RT at both validly and invalidly cued location, this effect

was greater when attention needed to shift to new locations in space. This pattern of results

(from Experiments 2 and 3) was also found in Experiment 4 in which the pulsed condition had a

greater influence on shifting attention to invalidly cued locations in a different attention task.

Why would there be a difference in the effect of task-relevant and task-irrelevant

manipulations of TC- and SC-processing on visual attention? It has been argued that the M

system serves as a guidance system in visual attention (e.g., Cheng, et al., 2004; Vidyasagar,

1999; Vidyasagar & Pammer, 1999). In the context of the present experiments, the pulse of the

pedestal (or surrounding region in Experiment 3) is believed to drive the response of MC cells

towards saturation (e.g., Leonova, et al., 2003; Pokorny & Smith, 1997; Smith & Pokorny,

2003). If this is true, then theoretically, the pulse would reduce the ability of transient channels

to respond to the target stimulus. If the M system (or transient channels) is less able to respond

to the target stimulus then, according to Vidyasagar’s (1999) theory, the M systems ability to

guide attention would be diminished. Therefore, with a reduced ability to guide attention in

space, the visual system would be slower to shift and respond to targets appearing in new (or

invalidly cued) locations. The pattern of results in the present experiments supports this, in that,

while RTs were slower overall in the pulsed conditions, the effect of the pulse was greater at

invalidly cued locations.

This difference in the way the S/PP paradigm influenced attention compared to previous

task-relevant manipulations was consistent across both object-based attention and IOR tasks.

Previous research on the relationship between IOR and transient and sustained channels has

indicated SC-biased conditions are associated with increased IOR magnitudes (Brown &

44

Guenther, in preparation; Guenther, 2008; Guenther & Brown, under review) whether created by

manipulations of stimulus spatial frequency (Brown, 2009; Brown & Guenther, in preparation)

or stimulus ramping (Guenther, 2008; Guenther & Brown, under review). The increased IOR for

these experiments was a result of SC-biased conditions having a greater effect on RTs at validly

cued locations (greater increases in RTs at cued compared to invalidly cued locations). Since

IOR is defined as an increase in RTs at validly cued locations, the increased RT at validly cued

location led to increases in IOR for those two experiments. In the present IOR experiment, the

pulsed (SC-biased) condition increased RTs most at the invalidly cued locations resulting in a

decrease in IOR.

Together with Experiments 2 and 3, the results of the IOR experiment provide convergent

evidence that the S/PP paradigm acts differently in attention tasks than previous task-relevant

manipulations (e.g., Brown, 2009; Brown & Guenther, in preparation; Brown, et al., under

review; Guenther, 2008; Guenther & Brown, under review) and is consistent in its effect. The

pulse condition always produced greater increases in RTs to targets appearing at invalidly

(compared to validly) cued locations. In the object-based attention task, this effect was manifest

as increased cost for both within-object and between-object shifts of attention which does not

influence the object advantage. In the IOR task, this effect was manifest as a greater increase in

RT for shifting attention to invalidly cued locations which decreased IOR magnitude. The

notion that the type of stimulus manipulation used (whether it is task-relevant or task-irrelevant)

may change the pattern of results warrants further study. An example of another manipulation

that could be employed to test this is through the use of full field flicker which (in the context of

the present attention tasks) is another task-irrelevant manipulation which can create SC-biased

conditions (e.g., Green, 1981; Nieuwenhuis, Jepma, Fors, & Olivers, 2008).

45

Object-based attention

There are several different accounts for the object advantage observed in object-based

attention tasks (e.g., Abrams & Law, 2000; Brown, et al., 2006; Shomstein & Yantis, 2002;

Vecera & Farah, 1994). While these accounts cannot sufficiently explain the influence of TC-

and SC-biased conditions observed in Brown et al (under review), the present experiments do not

offer additional challenges to these accounts. For example, while the biased attention

(Desimone, 1998; Desimone & Duncan, 1995) and attentional prioritization (e.g., Shomstein &

Behrmann, 2008; Shomstein & Yantis, 2002, 2004) accounts cannot explain the sensory

influence on the object advantage as reported by Brown et al (under review), the sensory

manipulation in the present experiments did not influence the object advantage. It is important to

note, although the present data does not challenge these accounts, they still cannot explain the

effect of the SC-biased pulsed conditions on validly and invalidly cued targets.

Of the different accounts for the object advantage, spreading attention (e.g., Abrams &

Law, 2000) and the emphasis on the disengage operation by Brown and Denney (2007) are the

most relevant to the present data. The spreading attention account is based on the notion that

attention naturally spreads out from fixation and that it is easier for attention to spread within the

boundaries of a single object than between two separate objects. In the present experiments, the

pulsed conditions may have been reducing the ability of the M system to guide attention (as

described by Vidyasagar, 1999). In the context of the spreading attention account, this could

have slowed the spreading of attention. This would result in an increased cost for shifting

attention for both between-object and within-object shifts of attention (in addition to the overall

increase in RTs resulting from the pulse). In regards to Brown et al (under review),

equiluminance could have also reduced the ability of attention to spread; however, there were

46

differences in the effect of equiluminance on within and between object shifts of attention which

cannot be explained by the spreading attention account.

Brown and Denney (2007) suggest, of the separate attentional operations (engaging,

disengaging, and shifting attention) necessary during an object-based attention task (or any cuing

task for that matter), the disengage operation is primarily responsible for the object advantage.

Brown et al (under review) also suggest, when the different attentional operations are examined

from a M and P perspective then within-object shifts of attention can be described as biased

towards space-based or M activity and between-object shifts of attention as biased towards

object-based or P activity. Their results indicate the equiluminant conditions had their greatest

effect on space-based attention thereby increasing the cost for within-object shifts of attention

and eliminating the object advantage. Unlike Brown et al (under review), the present

experiments employed a task-irrelevant manipulation of TC and SC processing which did not

have a differential effect for within- and between-object shifts of attention. These manipulations

then would not have differentially influenced the engage and disengage operations, instead,

pulsed conditions held their influence on the shifting attention operation.

Inhibition of return

Although IOR was originally described as a sensory (Posner & Cohen, 1984) rather than

an attention phenomenon, the attentional account (Posner, et al., 1985) has dominated later

research. The attentional account holds that IOR is an inhibition of attention to reorient or return

to previously attended locations. In this account it is necessary for attention to first be drawn to a

location, then away from that location, and the inhibition occurs when attention must return to

that previously attended location. Following this, IOR has been described as a mechanism to

facilitate efficient foraging behavior (for a review, see Klein, 2000). Although this attentional

47

account (Posner, et al., 1985) has been the focus of most IOR research, recent studies have again

highlighted the importance of sensory effects on IOR (e.g. Bell, et al., 2004; Brown, 2009;

Brown & Guenther, in preparation; Guenther, 2008; Guenther & Brown, under review; Reuter-

Lorenz, et al., 1996; Sumner, 2006; Sumner, et al., 2004).

One type of experiment challenging a purely attentional account of IOR are double-cuing

experiments (Posner & Cohen, 1984; Tassinari & Berlucchi, 1993). In a typical single-cuing

experiment, like that used here, a single cue appears in one of two possible locations followed by

a target that can appear either at the validly or invalidly cued location. In the double-cuing

experiments the cue appears simultaneously at both possible target locations. The double cue

(appearing at opposite locations) would not direct attention to a specific target location, then the

finding of inhibition matching that of single-cuing experiments (i.e., inhibition of a similar

magnitude was observed for single and double cuing experiments) cannot be accounted for by a

reorientation of attention account (since the double cue would not direct attention solely to the

target location but instead, split it to both locations). These experiments suggest sensory and

attentional components underlie IOR (Berlucchi, 2006). Similarly, when the cue is made

informative, the reorienting attention account would not predict IOR when the target location is

known in advance since there would be no need for attention to disengage from the cued

location. However, even with an informative cue, IOR is still found at the expected location

(Chica, Lupiáñez, & Bartolomeo, 2006).

Another challenge to a purely attentional account of IOR comes from the experiments

manipulating sensory characteristics of the stimuli (Brown, 2009; Brown & Guenther, in

preparation; Guenther, 2008; Guenther & Brown, under review). These studies manipulated the

cues and targets to bias the processing of the stimuli towards transient or sustained channels and

48

found increased IOR when stimuli were expected to reflect a SC-bias. A purely attentional

account would not predict differences in IOR to different spatial frequency targets (Brown, 2009;

Brown & Guenther, in preparation) or to ramped compared to abrupt targets (Guenther, 2008;

Guenther & Brown, under review). The presence of differences in IOR due to the sensory nature

of the stimuli, as with the double-cuing experiments, suggest a sensory component to IOR. The

present IOR experiment (Experiment 4) used a task-irrelevant manipulation of TC and SC

processing and again found manipulations designed to influence the sensory processing of the

stimuli influencd IOR. Together these experiments suggest IOR cannot be accounted for solely

by a reorienting attention account and that any model of IOR must include a sensory component.

Conclusions

The S/PP paradigm is a simple and flexible manipulation of TC and SC processing that

has been effective at illustrating the role of transient and sustained channels with a variety of

tasks and populations (e.g., Alexander, et al., 2003; Alexander, et al., 2004; Alexander, et al.,

2001; Alexander, et al., 2005; Delord, et al., 2006; McAnany & Levine, 2005, 2007;

McKendrick & Badcock, 2003; Puts, et al., 2005; Zele, et al., 2007). The present experiments

further demonstrate this flexibility to include attention tasks using RT as a measure. While

previous research has argued the importance of sustained channels (or the P system) in

attentional effects such as the object-advantage and IOR (e.g., Brown, 2009; Brown & Guenther,

in preparation; Brown, et al., under review; Guenther, 2008; Guenther & Brown, under review)

these studies have used manipulations of stimuli relevant to the task. The task-irrelevant nature

of the S/PP paradigm supports the importance of transient and sustained channels in the object-

advantage and IOR; however, it produces a different pattern of results than these previous

studies. The S/PP paradigm had its greatest influence on RT to invalidly cued targets. In object-

49

based attention, it resulted in a larger increase in RTs when attention had to shift to new locations

without influencing the object-advantage. In IOR, it again resulted in a larger increase in RTs to

invalidly cued locations, resulting in decreased IOR magnitudes. Current theories and accounts

of the object advantage and IOR do not sufficiently account for the differences reported in the

present experiments as well as those of Brown, Guenther and colleagues (e.g., Brown, 2009;

Brown & Guenther, in preparation; Brown, et al., under review; Guenther, 2008; Guenther &

Brown, under review). Future theories and accounts for these effects need to address these

sensory influences revealed through manipulations of relative processing of transient and

sustained channels.

50

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APPENDIX A

ANALYSES OF DATA EXCLUDED FROM EXPERIMENT 4

The number of participants eliminated (in Experiment 4) due to false alarms is high. It is

possible that the larger pedestal region used in this experiment increased the difficulty of the

task. The possibility that a larger pedestal region may increase the occurrence of false alarms is

an issue in which future experiments will be needed to explore further.

Due to the large number of false alarms, an additional analysis was conducted comparing

the data from the participants whose data was included vs. excluded from the analyses in

Experiment 4. For the data that was excluded the mean false alarm rate was 51% The RT data

were submitted to a 2 (pedestal direction: bright vs. dark) x 2 (pedestal: steady vs. pulsed) x 2

(validity: valid vs. invalid) x 2 (data: included or excluded) mixed ANOVA with

inclusion/exclusion as a between subjects variable. The main effect of data inclusion was not

significant. Two interactions reached significance resulting in an overall smaller pulse effect in

the excluded data and a greater difference in the magnitude of IOR between steady and pulsed

conditions for the excluded data. Importantly, the pattern and direction of the results was

consistent between both sets of data.

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Figure 1: Example of a pedestal. The pedestal is the central area (square) that is defined by a

luminance difference from the background.

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Figure 2: Experiment 2 Trial Sequence. Comparison between the sequence of events occurring

in steady- and pulsed-pedestal conditions (Example from Experiment 2).

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Figure 3: Example of a Traditional 4 Box Stimulus Design. Comparison between the sequence

of events occurring in steady- and pulsed-pedestal conditions in the traditional 4 box stimulus

design.

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Figure 4: Example of a Modified S/PP Paradigm. Example of a modified S/PP paradigm using

a large uniform pedestal region similar to that of McAnany and Levine (2007).

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Rea

ctio

n Ti

me

(ms)

300

325

350

375

400

425

450

475

500

Bright Pedestal Dark Pedestal

SteadyPulsed

Figure 5: RT data for Experiment 1. RT data (in ms) for Experiment 1 is plotted comparing the

effect of steady- and pulsed-pedestal conditions on RT for bright and dark pedestal conditions.

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Figure 6: RT data for Experiment 2. RT data (in ms) for Experiment 2 is plotted comparing the

effect of steady- and pulsed-pedestal conditions on RT for the different cuing conditions.

Steady Pedestal Pulsed Pedestal

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500 ValidInvalid WithinInvalid Between

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Figure 7: Effect of the Pulsed Condition on RTs in Experiment 2. Difference score plotting the

effect of the pulsed condition on RTs in Experiment 2 illustrating the increased effect of the

pulsed condition on invalidly cued trials. The Difference score was calculated by subtracting

RTs of steady-pedestal conditions from pulsed-pedestal conditions.

Puls

ed R

T - S

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T (m

s)

0

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Figure 8: Experiment 3 Trial Sequence. Illustration of the sequence of events in which the

background region is pulsed (Experiment 3).

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ed R

T - S

tead

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T (m

s)

0

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500 ValidInvalid WithinInvalid Between

Figure 10: RT data for Experiment 3. RT data (in ms) for Experiment 3 is plotted comparing

the effect of steady- and pulsed-pedestal conditions on RT for the different cuing conditions.

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Figure 11: Experiment 4 Trial Sequence. Illustration of the sequence of events for a trial in

Experiment 4.

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Figure 12: RT data for Experiment 4. RT data (in ms) for Experiment 4 is plotted comparing

the effect of steady- and pulsed-pedestal conditions on RT for the different cuing conditions.

Rea

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(ms)

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InvalidValid

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ed R

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tead

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s)

0

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100ValidInvalid

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