COGNITIVE PSYCHOLOGY 5, go-96 (1973)

Effects of Letter-Names on Visual Search1

LESLIE HENLIERSON~

University of Guelph, Guelph, Ontario, Canada

When a subject searches through a list of letters of mixed case in a letter cancellation task search is slowed if the background items include the target letter in the other case, This effect is largest when target and confusing background have visual analogue similarity (e.g., CC) but still obtains when no special visual similarity exists (e.g., aA). In searches for two targets, one of either case, search is facilitated when the targets are both cases of the same letter.

An enduring view of pattern recognition represents information process- ing as passing through a sequence of hierarchically ordered stages beginning with the analysis of simple physical features and proceeding through higher-order features to abstract and superordinate classes and names. This is the view which was cogently advanced by Neisser (1964) to account for the visual search performance of highly practised subjects searching for an unchanging target set. However other situations appear to involve simultaneous access to several levels of the processing hierarchy.

An acoustic factor in letter cancellation has been reported by Corcoran (1966) on the basis that subjects cancelling the e’s in a prose passage missed more silent than pronounced e’s. Similarly Corcoran and Weening (1968) report an effect in proofreading whereby subjects were less suc- cessful at detecting the omission of an initial k when the letter was silent as in “knack.” However, it is well known that the peculiar difficulty of proofreading consists of adhering to a graphemic level of analysis and that careful reading frequently involves subvocalisation but it is not clear that these facts have any general implication for the process of visual search.

Evidence from a situation which appears to support stronger inference is reported by Krueger (1970) who found that letter search was slower when the target was acoustically confusable with its background. How- ever Krueger’s effect is not robust. It only attains significance when the

‘This work was supported by a National Research Council of Canada grant to the author (A8263). Thanks are due to David Woodhouse for collecting data.

‘Mailing address: Department of Psychology, University of Guelph, Guelph, Ontario, Canada.

90 Copyright @ 1973 by Academic Press, Inc. All rights of reproduction in any form reserved.

LETTER-NAMES AND VISUAL SEARCH 91

data of both his experiments are combined. Inexplicably, the effect does not increase in magnitude when the list size is increased from 6 to 18 let- ters for Experiment 2 through total search time doubles. Also the effect is not present in Experiment 2 when the target is absent even though this entails exhaustive search. Finally the slowing attributed to acoustic confusability only amounts to about 3% and 134% of the RT in Experi- ments 1 and 2.

The present experiment investigates nonvisual aspects of search by utilizing that property of letters applied by Posner (1969) to the study of visual and name codes whereby upper and lower cases of a letter share the same name but differ physically in a manner ranging from a simple transformation (e.g., CC) to total dissimilarity (e.g., aA). In all cases the target is physically defined (by case). The attribute of letter-name is used in part 1 to attempt to slow search and is employed in a different way in part 2 in an attempt to facilitate search.

METHOD

Subiects. The Ss were five female undergraduate and graduate students serving as paid volunteers.

Materials. Materials consisted of 20 search lists in the manner of Gordon (1968). Each list consisted of a 25 X 40 item matrix of letters, single spaced. The background contained equal numbers of upper and lower case letters. Target frequency was invariably 5% and list randomisation was carried out within sub-matrices of 25 X 8 size. The target was printed at the top left of each list. All lists were typed and converted to high contrast copies.

Part 1 of the experiment refers to the first 12 lists. These lists were constructed from the letters, a, A, c, C, e, E. One of these six graphemes served as target in each of two lists, a confusable and nonconfusable list. The confusable list is so defined because the background contained the same letter in the other case. In all lists the background would comprise four letters, two of either case. Table 1 shows the targets and backgrounds for all lists.

In part 2 there were invariably two targets, one of either case. These targets were equiprobable with a combined frequency of 5%. The back- ground for the eight part 2 lists was invariably the same three letters in upper and lower case forms. The details are also represented in Table I which shows the two target pairs which consist of the same letter name. These lists are organised so that list 13 may be compared to I4 through 17 and list 18 compared to 16 through 20. In these comparisons the four lists which do not have same name targets contain one of the same name targets each, two lists having the lower case and two the upper.

92 LESLIE HENDERSON

TABLE 1 Target and Background Letters for the Search Lists. All Lists

Comprise 1000 Items with a Target Frequency of 50/;,

List Target(s) Background

Part 1. (The confusable background item is underlined.)

1 A e, E, c, C 2 A a, E, c, C 3 a E, e, c, C 4 a A, e, c, C - 5 C a, A, e, E 6 C c, A, e, E

7 c A, a, e, E 8 c C,, a, e, E 9 E a, A, c, C

10 E e, A, c, C 11 e c, c, a, A 12 e E, c, a, A

Part 2. (Same-name targets are underlined.)

13 aA L Background of

14 a, E s, S, 0, 0, n, N 15 e, A in all list8

16 a, C 17 c, A 18 CC L 19 c, E 20 e, C

Procedure. The lists were presented in random order with the constraint that the paired lists of part 1 were always adjacent in the series. The order was randomised for each subject and session. A session comprised the series of 20 lists. Each S performed six such sessions. The task was a cancellation search in which S searched the list from left to right, top to bottom drawing an oblique stroke through the targets. The experimenter presented a list, permitted S to inspect the target and then instructed S to start searching. At the expiry of 45 seconds S was instructed to stop, circling the item reached at the stop signal. Ss were instructed to try to avoid errors.

RESULTS

The total number of items searched in 45 set was recorded for each list and converted to letters searched per minute. The interference effect in part 1 is highly reliable. Table 2 presents the mean rate for each list. The

TABL

E 2

Perfo

rman

ce

on

each

lis

t av

erag

ed

over

Ss

and

Se

ssio

nsa

Part

1.

F;

Targ

et

A A

; i

C

c ;

ii 1c

E

e e

List

1

2 5

6 9

10

11

12

Fd

Mea

n se

arch

ra

te

720

648

557

516

928

711

594

512

714

661

526

478

z

Erro

r y0

1.

1 7.

9 1.

0 2.

2 1.

0 1.

1 2.

0 4.

1 1.

4 1.

3 1.

2 2.

8 Va

rianc

e of

diff

eren

ce

32.6

31

.5

161.

0 64

.9

30.8

37

.9

k

t 4.

89

2.81

3.

02

2.83

3.

44

2.83

P<

.O

l .0

5 .0

5 .0

5 .0

5 .0

5

Part

2.

d 4 Ta

rget

aA

aE

eA

aC

C

A cc

cE

eC

Li

st

13

%

14

15

16

17

18

19

20

Mea

n se

arch

ra

te

535

507

536

435

444

462

435

431

is

Erro

r y0

0.

0 0.

1 0.

2 0.

1 0.

5 0.

2 0.

4 0.

0 iz

f2

a

Sear

ch

rate

is

giv

en

in i

tem

s pe

r m

inut

e.

Erro

r 70

giv

es

the

frequ

ency

of

tar

get

omis

sion

s re

lativ

e to

the

nu

mbe

r of

tar

gets

ca

ncel

led.

In

pa

rt 1

list

num

bers

un

derli

ned

refe

r to

co

nfus

able

lis

ts.

94 LESLIE HENDERSON

data were collapsed over sessions and the differences between the paired lists with a given target were examined. Table 2 includes the variance of these differences and the outcome of t-tests for repeated measures. The comparison is significant for each target. Lists were also inspected for errors. There were no false positive errors. The rate of omissions is shown in Table 2. From the error data it is clear that subject performed fairly cautiously and there is no suggestion of a tradeoff. In fact errors tend to be more numerous in the confusable lists.

From Table 2 it is evident that upper-case searches are generally faster than lower case. It also seems that the largest interference effect obtains with the letter C as would be expected from the addition of shared visual similarity (linear transform) to shared name. On average the interference effect amounts to a slowing of about 10%.

Turning to part 2 we find a facilitatory effect of shared name when it pertains to the targets themselves though this is less consistent than the interference effect. An overall test of this effect can be made by considering lists 13, 16, 17 and I8 which contain permutations of targets a and c. Collapsing over same-name lists and different-name the com-

FIG. 1. Search rate in letters per minute for each session, averaged across subjects. The upper two functions represent Part 1 (interference effect) and the lower two functions represent Part 2 (facilitation effect) ; solid lines designate shared-name conditions ( see text ) .

LETTER-NAMES AND VISUAL SEARCH 95

parison significantly favors same-name (t = 4.24; p < .02). Furthermore the aA list is significantly easier than the average of the four other lists containing a’s (t = 3.62; p < .05) though the analogous comparison for the CC list falls short of significance (t = 1.45), despite the shared visual similarity in this case.

The main features of the results are summarized in Fig. 1, which shows the slowing effect of the confusable background in part 1 and the facilitatory effect of name-sharing in the two targets searched for in part 2. Performance improves more clearly in the two-target searches than the single target searches, consistent with Neisser’s ( 1964) findings. There is no suggestion, however, that either the interference (part 1) or facilitation (part 2) effects attenuate with practice over the range investigated.

DISCUSSION

The results demonstrate a nonvisual factor in letter search wherein name-sharing independent of visual similarity may be used to produce either a facilitatory or interfering effect. This might be regarded as a visual search analogue of the Stroop Test ( Stroop, 1935) but such a comparison is constrained by the fact that interference in the Stroop Test depends on the involvement of overt naming in the primary task and does not occur, for example, when the colours are merely searched (Uleman & Reeves, 1971) .

IS it useful to regard the name effect as an acoustical effect in the sense of Corcoran and Krueger? For Krueger this effect is mediated by implicit speech during search. This interpretation is difhcult to maintain, as Krueger himself notes (1970, p. 399), both because his Ss deny sub- vocalising background letters and because the effect does not increase when list length is trebled. An even more basic objection seems to be that search is twice as fast as upper estimates of implicit speech with unfamiliar sequences. However a process for the analysis of names which operates considerably faster than implicit speech is not unthinkable. Brand ( 1971) has reported that digit versus letter category membership may function as a more efficient search dimension than shape; a digit is found faster among letters than a letter target, and the converse is also true.

Whatever the level of abstraction of the name code these results sug- gest that analysis of spatial features and of names proceeds in parallel as has been suggested in the context of same-different judgments (Posner, 1969) and tachistoscopic letter recognition (Scarborough, 1972; Hender- son, 1972). As in the Stroop Test, it is difficult to suppress the reading- naming process. Although there is no tendency to false-positive errors

96 LESLIE HENDERSON

in search this may simply reflect a lack of the verbal response competition which characterises the Stroop Test.

With parallel name and shape analysis it is unnecessary to postulate a serial naming mechanism operating as fast as the obtained search rate. Given that the name and shape analysers operate on several characters at once any overlap in the distribution of their processing latencies for an input frame is sufficient to mediate a name effect.

REFERENCES

BRAND, J. Classification without identification in visual search. Quarterly Jou7nal of Experimental Psychology, 1971,23, 178-186.

CORCO~AN, D. W. J. An acoustic faotor in letter cancellation. Nature, 1966, 210, 658. CORCORAN, D. W. J., & WEENING, D. L. Acoustic factors in visual search. Quarterly

Joud of Experimental Psychology, 1968,20,83-85. &~DON, I. E. Interaction between items in visual search. Journal of ExpeTimental

Psychology, 1968, 76,348-355. HENDERSON, L. Spatial and verbal codes and the capacity of STM. Quarterly Journal

of Experimental Psychology, 1972, 24, 485-495. KRUEGER, L. E. The effect of acoustic confusability on visual search. American

Journal of Psychology, 1970, 83,389400. NEISSER, U. Visual search. Scientific American, 1964, 210, 94-102. POSNER, M. I. Abstraction and the process of recognition. In Bower, G. H. and

Spence, J. T. (Eds. ) Psychology of Learning and Motivation. New York: Academic Press, 1969. Vol. 3.

SCARBOIKXJGH, D. L. Memory for brief visual displays of symbols. Cognitive Psy- chology, 1972, 3,408-429.

STROOP, J. R. Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 1935, 18, 643-661.

ULEMAN, J. S., & REEVES, J. A reversal of the Stroop interference effect through scanning. Perception and Psychophysics, 1971, 9, 293-295.

(Accepted October 23, 1972)