Topic A: Psychophysical Methods & TSD

Question 1

Response Compression

Answer 1

the result when doubling the physical intensity of a stimulus less than doubles the subjective magnitude of the stimulus

Question 2

Response Expansion

Answer 2

the result when doubling the physical intensity of a stimulus more than doubles the subjective magnitude of the stimulus

Question 3

Power Functions

Answer 3

a mathematical function of the form P=KS^n, where P is perceived magnitude, K is a constant, S is the stimulus intensity, and n is an exponent

Question 4

Steven’s Power Law

Answer 4

a law concerning the relationship between the physical intensity of a stimulus and the perception of the subjective magnitude of the stimulus

the law states that P=KS^n, where P is perceived magnitude, K is a constant, S is the stimulus intensity, and n is an exponent

Question 5

Response Criterion

Answer 5

in a signal detection experiment, the subjective magnitude of a stimulus above which the participant will indicate that the stimulus is present

Question 6

Signal Detection Approach

Answer 6

an approach to detection of stimuli in which subject’s ability to detect stimuli is measured and analyzed in terms of hits and false alarms

the approach can take a subject’s criterion into account in determining sensitivity to a stimulus

Question 7

Hit

Answer 7

in a signal detection experiment, saying “Yes, I detect a stimulus” on a trial in which the stimulus is present (a correct response)

Question 8

Miss

Answer 8

in a signal detection experiment, saying “No, I don’t detect a stimulus” on a trial in which the stimulus is present (an incorrect response)

Question 9

False Alarm

Answer 9

in a signal detection experiment, saying “Yes, I detect the stimulus” on a trail in which the stimulus is not presented (an incorrect response)

Question 10

Correct Rejection

Answer 10

in a signal detection experiment, saying “No, I don’t detect a stimulus” on a trial in which the stimulus is not presented (a correct response)

Question 11

Receiver Operating Characteristic (ROC)

Answer 11

a graph in which the results of a signal detection experiment are plotted as the proportion of hits versus the proportion of false alarms for a number of different response criterion

Question 12

Noise

Answer 12

in signal detector theory, noise is all of the stimuli in the environment other than the signal

Question 13

Signal

Answer 13

the stimulus is presented to a participant

a concept in signal detection theory

Question 14

What is classical psychophysics?

Answer 14

study the relationship between physical qualities and the experience of them

can be used to understand detection, discrimination, and scaling of physical stimuli

Question 15

What is the absolute threshold?

Answer 15

minimal limit of sense modality

also called limen

point at which physical stimulation enters into consciousness (threshold theory)

minimum stimulus energy (or chemicals) required to be detected 50% of the time

Question 16

What is the method of constant stimuli?

Answer 16

stimulus values chosen at random from a predetermined (“constant”) set

1. select intensity range: 0 to 100 lumens
2. determine set of values: 8, 97, 42, 8, 67, 4, 35, 51, …
3. observer says “yes” when stimulus is perceived
4. records observations (“trials”)
5. plot results

at threshold, the probabilities of saying “yes” and “no” are equal

Question 17

What is the pro of the method of constant stimuli?

Answer 17

gives good estimate of threshold

Question 18

What is are the cons of the method of constant stimuli?

Answer 18

time-consuming (must know proper range)

cannot measure threshold changes over time (e.g., in dark adaptation)

Question 19

What is the method of limits?

Answer 19

change stimuli intensity monotonically

ascending series: stimulus values increased until perceived

descending series: stimulus values reduced until not perceived

Question 20

What is the pro of the method of limits?

Answer 20

can track threshold changes over time

Question 21

What are the cons of the method of limits?

Answer 21

induces errors of habituation
induces errors of anticipation

Question 22

What is adaptive testing?

Answer 22

stimuli presented in a continuous series

“staircase” method: changes from ascending to descending when “yes” encountered; vice versa for “no”

change start point for a series from trial to trial

threshold may vary between trials; take the mean

Question 23

What is the method of adjustment?

Answer 23

observer directly controls stimulus values until threshold reached

Question 24

What is the pro of the method of adjustment?

Answer 24

fast

Question 25

What is the con of the method of adjustment?

Answer 25

least accurate method

Question 26

What is the difference threshold?

Answer 26

minimum difference needed to discriminate between two stimuli, 50% of the time

judgment made between standard and comparison stimuli (both are well above absolute threshold)

a.k.a. “just noticeable difference” or JND

e.g., 100 g standard vs comparison stimuli; is comparison heavier

Question 27

What is the point of subjective equality (PSE)?

Answer 27

stimulus that is apparently most like the standard

e.g., could think 99g is the same as 100g

PSE may differ from standard stimulus

Question 28

What is Weber’s Law?

Answer 28

is the difference threshold the same for all standard stimuli, or does it vary somehow?

e.g., for a 100g weight, JND = 3g (difference = 3%)
for a 1,000g weight, JND = 30g (difference = 3%)
Weber fraction = 3/100 = 0.03

Question 29

What are the problems with Weber’s Law?

Answer 29

“law” does not extend to extremes

cannot be applied to stimuli close to absolute threshold

also breaks down at higher stimulus intensities

Question 30

What is scaling?

Answer 30

what is the magnitude of the stimulus?

e.g., are two 60 W lights twice as bright as one 60 W light?

Question 31

What is indirect scaling?

Answer 31

magnitude derived from multiple difference judgements

Question 32

What is Fechner’s Law?

Answer 32

derived a scale based on two assumptions:
Weber’s law is valid
basic perceptual unit is the JND

e.g., what if intensity is doubled? let k = 1
if I = 100, S = 4.61
if I = 200, S = 5.30 (not double 4.61)

doubling intensity does not make stimulus seem twice as big

Question 33

What are the problems with Fechner’s Law?

Answer 33

Webber’s law breaks down at extremes

research showed Fechner’s formulation was insufficient

Question 34

What is direct scaling?

Answer 34

observers assign values to stimulus intensities

Question 35

What is magnitude estimation?

Answer 35

1. observer presented with a reference stimulus (modulus); and a certain value (say, 10)
2. other stimuli are presented; observer assigns values to them (if half as bright, give it a 5; if twice as bright, 20, etc.)

values of stimulus magnitude provided directly by observer

results conflicted with Fechner’s Law

Question 36

What is Steven’s Law?

Answer 36

P = KS^n

Question 37

What do the variables in P = KS^n mean?

Answer 37

P = perceived magnitude
S = stimulus intensity
K = constant
n = exponent

Question 38

How does the exponent in Steven’s law express the nature of the relation?

Answer 38

n > 1: response expansion (e.g. doubling voltage more than doubles sensation of electric shock)

n = 1: linear relation: magnitude of response matches changes in physical quantity (e.g. estimates of line length, distance)

n < 1: response compression (e.g. doubling intensity of light produces only a small change in perceived brightness)

Question 39

What were the criticisms of Steven’s Law and their solutions?

Answer 39

criticism: the lines describing Steven’s law look very different
solution: plot a log-log graph

criticism: why does the system operate this way?
answer: evolution (pain very quickly becomes aversive, estimating distances is very accurate, allow is to handle a large range of light intensities)

criticism: magnitude estimation may tell us how people “use numbers” instead of how they judge stimuli
solution: cross-modality matching

Question 40

What is cross-modality matching?

Answer 40

one sense is used to provide a measure of intensity in another sense

typically uses a hand dynamometer

grip squeezed to indicate magnitude of stimulus

kinanesthesia used to estimate quantity in other modality

results match magnitude estimation

Question 41

How was the problem of observers saying “yes” a lot in signal detection experiments solved?

Answer 41

“response bias” confounds attempts to measure sensitivity

solution: “catch trails” where no stimulus is presented in half the trials
help determine whether observer has a tendency to response “yes” (or “no”) more frequently

Question 42

What is the receiver operating characteristic (ROC) curve?

Answer 42

each point represents a different payoff

note: stimulus value has remained constant

“bowing” of curve affected by: observer’s sensitivity and intensity of the stimulus

Question 43

What is subliminal stimuli?

Answer 43

a stimulus that is below threshold may be consciously detected up to 49% of the time

however, a subliminal stimulus is below threshold, and does not enter awareness

can we (unconsciously) sense subliminal stimuli?

will this information affect us without our awareness?

Question 44

What was the Murphy & Zajonc (1993) study asking if we can process information without awareness?

Answer 44

had observers rate liking of Chinese characters out of 5

each character preceded by a priming stimulus: positive affective (happy face photo), negative affective (scowling face photo), irrelevant (geometric shape), no prime

results: no liking differences in optimal prime condition, facial expression affected liking in subliminal condition, stimuli can affect us outside of our awareness, but they create a feeling, not awareness or action

Question 45

What was the Vokey & Read (1985) study on if backward messages can be perceived?

Answer 45

played Lewis Carroll’s (1871) “Jabberwocky” and Psalm 23 backwards

observers were equally likely to identify reverse-played psalms as pornography and vice versa

listeners had no idea what was being said, or what it was about

backward messages are not perceivable

Question 46

What was the Cheesman & Merikle (1984) study?

Answer 46

1. presented congruent or incongruent “prime”; colour-name word
2. presented visual “mask” of random letters
3. presented color patch “target”

task: name target colour: 1 of 4 colour patches

suprathreshold prime: congruent named 95 ms faster than incongruent (100% correct; chance = 25%)

subliminal prime: congruent named 40 ms faster (66% correct)

subjectively imperceptible (but objectively detectable) stimuli may affect responses

Question 47

What was the Spangenberg, Obermiller, & Greenwald (1992) study?

Answer 47

double-blind study assessed subliminal message self-help audiotapes (e.g. self-esteem, weight loss, memory ability)

subliminal messages ineffective at inducing any change: “illusory placebo effect”

however, labels on the tape (not correlated with the content) influenced perceived effectiveness