Measuring Behavior, Cognition and Perception Techniques for learning how the brain works Lesion...

Measuring Behavior, Cognition and Perception

Techniques for learning how the brain works

• Lesion• Clinical case studies• Electrical brain stimulation• Transcranial magnetic stimulation• Recording gross electrical activity (ERP)• Single cell recording• Neuropharmacology• Brain imaging• Experimental psychology

Techniques for learning how the brain works

• Lesion• Clinical case studies• Electrical brain stimulation• Transcranial magnetic stimulation• Recording gross electrical activity (ERP)• Single cell recording• Neuropharmacology• Brain imaging• Experimental psychology

Classical and operant conditioning

Psychophysics

Reaction time

Epistemology - the origins of knowledge

• nativism - the order we perceive in nature is the order our minds impose on nature


• nativism

• empiricism


“Imagine a man born blind and taught by his touch to distinguish between a cube and a sphere. If the blind man were made to see,

would he be able to distinguish the two shapes based on sight alone?”

“The blind man would not be able to say which was the globe and which the cube

whilst he only saw them.”

Naïve Realism - the world is as the world appears to the mind;

all ideas and perceptual experiences are creations of the

mind“All the choir of heaven and furniture of the earth … have not any subsistence

without a mind, that their being is to be perceived or known.” (

recall Whitehead’s quote)

“ [objects] are perceived as with qualities that in reality do not belong to them, qualities which are

in fact purely the offspring of the mind. Thus nature gets credit which should in truth be

reserved for ourselves: the rose for its scent; the nightingale for his song; and the sun for its

radiance. The poets are entirely mistaken. They should address their lyrics to themselves and

should turn them into odes of self-congratulations on the excellency of the human

mind. Nature is a dull affair, soundless, scentless, colourless; merely the hurrying of

material, endlessly, meaninglessly.”

Science and Medicine

Johannes Muller (1801-1858)

Law of Specific Nerve Energies

• one is directly aware of nerve impulses, not external world (recall Mountecastle’s quote)

• different nerves/brain areas create different sensations

• same stimulus applied to different nerves elicits different sensations

• different stimuli applied to same nerve elicit same sensation

Science and Medicine

Gustav Fechner (1801-1887)

Elements of Psychophysics

• consumed with relation of mind to brain

• variations in mental intensity is proportional to variations in physical intensity (∆I/I) = constant

• formulated psychophysical techniques

http://serendip.brynmawr.edu/exhibitions/Mind/Consciousness.html

Experimental Psychology

Wilhelm Wundt (1832-1920)

Structuralism

• established first laboratory for experimental study of psychology (1879)

• study of consciousness and perception

Experimental Psychology

Ivan Pavlov (1849-1936)

Classical conditioning

• established technique for behaviorally studying non-human species

• study of stimulus discrimination

Strategies for Studying Perception

• What do things look like? (phenomenology)• What are the limits to perception? (thresholds)• What are the scaling properties of perception (ME &

MDS)• When does perception produce mistakes (study of

illusions)• Where in the brain does perception occur? (fMRI)• When does perception fail? (clinical neurology)• How does perception vary among individuals and

among species?

Phenomenology

Colors appear more saturated toward dusk

Moon looks larger when on the horizon

High frequency sounds are more difficult to localize

Food tastes bland when your nose is stopped up

Object size influences perceived weight

Viewing real motion subsequently produces experience of illusory motion

QuickTime™ and aAnimation decompressorare needed to see this picture.

PsychophysicsInvented by Gustav Fechner in 1860

Three measures of importance:

• absolute threshold - the lower limit of perception; weakest stimulus that can just barely be detected• difference threshold - smallest reliably discriminable difference between two stimuli

• point of subjective equality - magnitude of one stimulus at which it is perceived as equivalent in magnitude to another

• absolute threshold - the lower limit of perception; weakest stimulus that can just barely be detected

• difference threshold - smallest reliably discriminable difference between two stimuli

• point of subjective equality - magnitude of one stimulus at which it is perceived as equivalent in magnitude to another

Techniques for Measuring Thresholds and PSEs

method of adjustment - person adjusts stimulus to value where it is barely detectable (absolute threshold) or adjusts one stimulus until it matches another (difference threshold/PSE)

method of limits - experimenter changes stimulus by small amounts to find point where person’s judgment of stimulus first changes

method of constant stimuli - present stimuli (or pairs of stimuli) one at a time; person responds “yes” or “no” following each presentation, generating a psychometric function

Psychometric Function

Looking at the two horizontal lines, which is

longer?

.

100001000100

Frequency (Hz)

3

4

5

6

7

8

.

1210864200.00

0.25

0.50

0.75

1.00

Stimulus intensity

.

864200.00

0.25

0.50

0.75

1.00

Stimulus intensity

A psychophysical function from a set of psychometric functions

.

864200.00

0.25

0.50

0.75

1.00

Stimulus intensity

.

100001000100

Frequency (Hz)

3

4

5

6

7

8

An “audiogram”

Problem of criterion

“.. we must never take a person’s testimony, however sincere, that he has felt nothing, as proof positive that

no feeling has been there.” W. James, 1890

Problem of criterion

• perceptual decisions are influenced not only by person’s sensory abilities but by the individual’s motivations and expectations• willingness to say “yes” or “no” in threshold experiments depends on the consequences of those responses (rewards and costs)• willingness to say “yes” or “no” depends on likelihood (i.e., the probability) of an event• performance differences among people (or among groups of people) could be attributable, in part, to criterion differences

• Set of assumptions and procedures for measuring perceptual performance (decision making) under conditions of uncertainty, the goal being to distinguish performance changes/differences attributable to sensitivity vs criterion

• Applies to any situation where a binary decision must be made under conditions of uncertainty or doubt - make an observation and draw a conclusion

Signal Detection Theory (SDT)

- detecting faint sounds (e.g., murmur heard through stethoscope)

- diagnosing X-ray images (e.g., “is it a tumor?”)

- interpreting “blips” on a radar screen (“plane vs flock of birds”- stock market transactions (“buy or sell?”)

- jury decision (“innocent vs guilty”)

- deciding whether or not two lines are identical in length

tumorpresent

no tumor

Doctor's diagnosis

sickwell

correct

correct

incorrect

incorrect

Accused is guilty

Accused isinnocent

Jury decision

correctverdict Error

guiltyinnocent

correctverdictError

"no"

stimulus event

person'sresponse

hit falsealarm

miss correctrejection

present absent

"yes"

• Discrete observations occasioned by presence of “noise” only or “signal plus noise”

- “noise” is anything that complicates detection of “signal” by introducing uncertainty about whether or not the signal is present

distracting background noise in a hearing task

misleading evidence in a legal trial

flock of birds on a radar screen

scar tissue on a mammogram

- Strength of signal relative to background level of noise- Person’s sensitivity to the signal- Relative frequency of occurrence of the signal- Person’s level of motivation- Costs associated with hits and false alarms

Signal detection theory measures sensitivity independent of criterion - Assume each observation produces given amount of information - Amount of information varies from observation to observation - Person “measures” the amount of information on each trial and decides whether signal was present or notFour possible outcomes:

- Signal was present and person says “yes” - HIT- Signal was present and person says “no” - MISS- Signal was not present and person says “no” - CORRECT REJECTION- Signal was not present and person says “yes” - FALSE ALARM

Factors that influence person’s willingness to say “signal present”

“noise” “signal + noise”

Magnitude of sensory response

Strong response -- signal highly likely

Weak response -- signal highly unlikely

“noise” “signal + noise”


moderate response -- signal or noise?


criterioncriterion criterion


criterion


criterion

“hit”“miss”

“Signal present”

“no” “yes”


criterion

“false alarm”

“correct rejection”

“Signal absent”

“no” “yes”


criterion

"no"

stimulus event

person'sresponse

hit falsealarm


present absent

"yes"

criterioncriterion


criterion

"no"

stimulus event

person'sresponse

hit falsealarm


present absent

"yes"


criterion


criterion

Receiver Operating Characteristic: ROC


criterion

Receiver Operating Characteristic: ROC

d’

Psychophysical Scaling Techniques

Scaling - establishment of a quantitative metric expressing the relation among a sequence of stimuli. Scaling involves the assignment of numbers (scale values) to psychological attributes

Nominal scales - arbitrary assignment of numbers to objects, with no order implied; nominal scale values simply identify or categorizeOrdinal scales - objects arranged according to the order of their magnitudes (e.g., smallest to largest ), but with no reference to the spacing between stimuli; ordinal scale items obey the principle of transitivity: if a<b and b<c, then a<c

Interval scales - ordered stimuli in which the magnitude of the differences among various stimuli is meaningful

Ratio scales - ordered stimuli in which magnitude and ratio of values is meaningful

Just noticeable differences and psychological scales

Perceived size measured using the method of paired comparisons

.

Actual circle size

100

0

50

standard

PSE

.

Actual circle size

100

0

50

standard

jnd

75

Ratio Scaling of Sensory Experience: Magnitude Estimation

Magnitude estimation is a procedure where people directly assign numbers to stimuli in proportion to the perceived intensity of those stimuli. The procedure allows us to study the way in which perceived intensity grows with physical intensity. People are assumed to be “instruments” that can directly measure themagnitude of a sensory event.

Magnitude Estimation: Loudness

Assign a number proportional to the loudness of the following

sound bursts

Assign this sound loudness a magnitude of

“100”

Rate the loudness of these sounds relative to

the “standard”

standard

A B C D E

.

Physical unit of measurement

painsize

loudness

• works for psychological variables where there exists one underlying dimension that can be scaled in physical units

.

Physical magnitude

brightness

sizepain

Multidimensional Scaling

How can we derive scales for objectsthat vary along multiple dimensions?

Learning about Perception From Studies of Nonhuman Subjects

• reflex reactions (e.g., alarm calls)

Altered alarm whistle (blank)

Normal alarm whistle

Altered alarm whistle (noise)


• reflex reactions (e.g., curiosity)

QuickTime™ and aSorenson Video decompressorare needed to see this picture.


• reflex reactions (e.g., alarm calls)

• operant conditioning (discrimination training)

Learning about Perception From Studies of Human Infants

Preferential looking technique

Learning about Perception From Studies of Human Infants

Reaction time: A Behavioral Index of Mental Events

Hermann von Helmholtz (1821-1894)

Treatise on Physiological Optics

• measured the speed of neural impulses (27 m/sec)

• developed trichromatic color theory

• developed pitch theory of hearing

• proposed that perception involves unconscious inference

Reaction time as an index of cognitive processing

Same/Different judgments: reaction time on speeded decisions reflects stages of processing

Same/Different RT

Are the two letters physically “same” or “different”?

a a

Same/Different RT


s s

Same/Different RT


f e

Same/Different RT


n n

Same/Different RT


p z

Same/Different RT

Do the two letters have the “same” name?

c R

Same/Different RT


Mm

Same/Different RT


d d

Same/Different RT


F T

Same/Different RT


B b

Same/Different RT


e e

.

eE

eeee

physicalsame

namesame

Same/Different RT

Mental Rotation: Use of reaction time to study mental imagery

Normal or backward?

Mental Rotation: Use of reaction time to study mental imagery

.

deviation from upright (degrees)

0 9090180 180CCW CW

Use of RT together with error rate data to draw inferences about mental processing. Try

this simple color naming test:xx xx xx xx xx xx

xxxxxxxxx

xxxxxxxxxxxxxxxxxxxxxxxx

xxxxxxxxxxxxxxx

bluegreenyellow

redyellowpurplepurplewhitebluered

greenyellow

The Stroop Effect: A Demonstration of Attentional Interference

Discovered by John Ridley Stroop, PhD Peabody College 1933 (his

dissertation)

Using RT to study attention: See if you notice anything strange happening in the scene I’m about to show

you?

Notice anything strange happening in this scene?

Notice anything strange happening in this scene?

“Change blindness”

You will be shown list of words divided into two columns. Do your best to memorize these words; your ability to remember them will be tested in a

moment

Learning from Mistakes: Patterns of Errors Reveal Properties of the Structure of Memory

• Bed• Rest• Awake• Tired• Dream• Wake• Snooze• Blanket• Slumber• Snore• Nap• Yawn• Drowsy

• Hot• Snow• Warm• Winter• Ice• Wet• Frigid• Chilly• Heat• Weather• Freeze• Air• Shiver

Now the test! As I call off the words in the next slide, say out loud “yes” or “no” to indicate

whether or not the word was among the ones you memorized.

• Snore• Heat• Dance• Tired• Dream• Balloon• Snooze• Blanket• Breakfast• Slumber• Fever• Sleep• Lawn• Frigid• Shiver

• Frost• Guide• Snow• Warm• Winter• Flower• Wet• Belt• Chilly• Family• Cold• Freeze• Air• Shave• Awake

• Snore• Heat• Dance• Tired• Dream• Balloon• Snooze• Blanket• Breakfast• Slumber• Fever• Sleep• Lawn• Frigid• Shiver

• Frost• Guide• Snow• Warm• Winter• Flower• Wet• Belt• Chilly• Family• Cold• Freeze• Air• Shave• Awake

False memories created by context

The more mental effort required by a task, the longer it takes to complete the task but the more long lasting the effects:"Depth of Processing" Demonstration

You will be shown a list of words. Read through the list quickly and for each word silently name a synonym

for that word.

apple = fruitsimple = easy

You will be shown a list of words. Read through the list quickly and for each word silently name the

font in which the word is printed.

apple = "Courier"simple = "Chicago"

elephant simple leaves jingle trumpet cause

damage glory belt nurse alley smart tingle seize

Now you're going to see a longer list of words. As I call off the

word, you yell out whether it's an "old" word (one that

appeared on the previous list) or a "new" one.

Which of these were on the previous list?

_ flower_ chalk_ leaves_ derivative_ alley_ smart_ garage_ orange_ delicate_ easy

_ children_ damage_ trumpet_ victory_ duck_ glamour_ jingle_ butter_ snow_ nurse

“deep” processiing promotes retention

Summary of Strategies for Studying Behavior and Cognition

• Classical and operant conditioning• Psychophysical techniques• Scaling techniques• Reaction time• Error patterns

Measuring Behavior, Cognition and Perception Techniques for learning how the brain works Lesion...

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