Psychophysics

Question 1

What is psychophysics

Answer 1

Quantitative branch of the study of perception

Question 2

What does psychophysics examine

Answer 2

The relations between observed stimuli and responses, as well as the reasons for those relations

Question 3

Who founded psychophysics

Answer 3

Gustav Fechner

Question 4

When was psychophysics founded

Answer 4

October 22, 1850

Question 5

What was Gustav Fechner seeking to do when founding psychophysics

Answer 5

Wanted to calibrate the mind relative to physical stimuli

Question 6

What is the first requirement in a psychophysics experiment

Answer 6

Human/nonhuman subjects are tested in an expirimental environment that maximizes control of stimulus variations over variations in the subjects responses

Question 7

What is the second requirement of psychophysics experiments

Answer 7

Stimuli carefully controlled, often varying along only a single physical dimension (ex: intensity)

Question 8

What is the third requirement for psychophysics experiments

Answer 8

Subject’s responses are highly contrained (ex: “yes, i see stimulus” or “no i dont see stimulus”)

Question 9

What is the fourth requirement of psychophysics experiments

Answer 9

Small numbers of subjects are tested with extensive within-subject designs

Question 10

What do psychometric functions typically look like

Answer 10

Sigmoid “S” shape with the x variable being invisible near zero and visible near 100, and the y variable being percent that said “yes”

Question 11

What are the three types of measurements in a psychophysics experiment

Answer 11

Absolute threshold
Difference threshold
Point of subjective equality (PSE)

Question 12

What is the absolute threshold

Answer 12

Lower limit of perception; weakest stimulus that can just barely be detected

Question 13

What is the difference threshold

Answer 13

Smallest reliably discriminable difference between two stimuli

Question 14

What is difference threshold also known as

Answer 14

JND (just noticeable difference)

Question 15

What is the point of subjective equality (PSE)

Answer 15

Magnitude of one stimulus at which it is perceived as equivalent in magnitude to another

Question 16

What percentage of people are able to notice the PSE

Answer 16

50

Question 17

What percentage of people are able to notice the JND

Answer 17

75

Question 18

What is the x axis gap between the PSE and JND known as

Answer 18

IND

Question 19

What are the two techniques for measuring thresholds and PSEs

Answer 19

Yes-No Tasks
X AFC Tasks

Question 20

What are Yes-No Tasks

Answer 20

NO option is the absence of something; typically used in detection tasks

Question 21

Are Yes-No Tasks subject to bias?

Answer 21

Yes. Bias is corrected by the SDT

Question 22

What happens in Yes-No Tasks when the participant is unsure

Answer 22

Answer is guided by personal biases

Question 23

How is the threshold determined in Yes-No Tasks

Answer 23

Threshold set to 50%

Question 24

What are X AFC Tasks

Answer 24

A choice between multiple, corresponding alternatives; used in discrimination tasks

Question 25

Are X AFC Tasks subject to bias

Answer 25

No

Question 26

What happens when subjects in X AFC Tasks are unsure

Answer 26

They're forced to guess

Question 27

What is the "pure" guessing performance determined by in X AFC (with example)

Answer 27

X (example, for 2 AFC = 50%, 4 AFC =25%)

Question 28

What does the guessing range determine

Answer 28

The lower performance limit

Question 29

What is the threshold set to in X AFC tasks

Answer 29

Set to halfway between the guessing rate and 100%

Question 30

What are the three procedures for measuring thresholds and PSEs

Answer 30

Method of adjustment/limits Method of constant stimuli Staircase method

Question 31

What is the method of adjustment/limits

Answer 31

Person adjusts stimulus to value where it is barely detectable (absolute threshold) or adjusts one stimulus until it matches another (PSE) or differs from another (JND)

Question 32

What is the difference between the method of adjustment and the method of limits

Answer 32

Adjustment: Stimulus adjusted by subject Limits: Stimulus is manipulated by the experimenter or a computer program

Question 33

How are the results of the method of adjustment/limits measured

Answer 33

Lower/raise until just barely detectable Repeat X number of times Average the values to estimate the threshold

Question 34

What is the method of constant stimuli

Answer 34

Present stimuli at various levels; person responds (ex: yes or no) following each presentation, generating a psychometric function

Question 35

Describe method of constant stimuli in depth

Answer 35

Display stimuli in random order and repeat many times For each trial, subject indicates their perception of the stimuli Plot subjects' answers as response probablility vs stimulus value Estimate the threshold and/or slope

Question 36

How many times should the constant stimuli method be repeated per stimulus level

Answer 36

~40

Question 37

What is the staircase method

Answer 37

Adaptive search for threshold

Question 38

What does a subject's response (correct/incorrect) determine in the staircase method

Answer 38

Correct -> following trial is harder Incorrect -> following trial is easier

Question 39

What are the two types of staircase method

Answer 39

Fixed step size Adaptive step size (asking where somebody is from analogy)

Question 40

What is the staircase method designed to do

Answer 40

Converge to a certain threshold value

Question 41

What are the pros of the constant stimuli method

Answer 41

Gold standard of psychophysics Yields a complete psychometric function

Question 42

What are the cons of the constant stimuli method

Answer 42

Takes many trials Requires pre-selecting stimulus levels

Question 43

What are the pros of the staircase method

Answer 43

Fastest method for estimating threshold Doesnt require pre-selecting stimulus levels, just the starting point Great for non-expert subjects

Question 44

What are the cons of the staircase method

Answer 44

Does not yield a complete psychometric function Focuses on estimating the threshold