Module Seven - Psychophysics Flashcards
(106 cards)
1
Q
What does psychophysics study?
A
How physical stimulus properties relate to perceptual responses.
2
Q
What are common types of perceptual responses?
A
Describing, recognizing, detecting, perceiving magnitude, and searching.
3
Q
What is describing in perceptual response?
A
Noting characteristics of a stimulus (e.g., all of the people in the student section are wearing red).
4
Q
What is recognizing in perceptual response?
A
Assigning a stimulus to a category (e.g., number 12 is the other team’s quarterback).
5
Q
What is detecting in perceptual response?
A
Becoming aware of a barely perceptible stimulus (e.g., that lineman moved slightly just before the ball was snapped).
6
Q
What is perceiving magnitude?
A
Judging size or intensity (e.g., that lineman looks twice as big as our quarterback).
7
Q
What is searching in perceptual response?
A
Looking for a specific stimulus among others (e.g., I’m looking for Susan in the student section).
8
Q
What is the phenomenological method?
A
Observers describe what they perceive or indicate when a perception occurs.
9
Q
What type of observations does the phenomenological method yield?
A
Basic observations (e.g., depth perception, color qualities, taste qualities) that form the starting point for explaining perceptual phenomena.
10
Q
What is the recognition method?
A
Presenting a stimulus and having the observer name or categorize it.
11
Q
In what contexts is the recognition method used?
A
Patient studies with brain damage or visual agnosia, often using pictorial stimuli rather than real objects.
12
Q
What is the absolute threshold?
A
The smallest amount of stimulus energy needed to detect a stimulus (e.g., minimum light intensity to perceive a flash).
13
Q
Who proposed classical psychophysical methods for measuring absolute threshold?
A
Fechner.
14
Q
What are Fechner’s three methods for measuring absolute threshold?
A
Method of limits, method of adjustment, and method of constant stimuli.
15
Q
What is the method of limits?
A
Present stimuli in ascending or descending intensity series; observer responds ‘yes’/’no’ at each intensity; threshold is the mean of crossover points.
16
Q
What is a crossover point in the method of limits?
A
The intensity at which the observer’s response changes from ‘yes’ to ‘no’ or vice versa.
17
Q
What is the method of adjustment?
A
Observer (or experimenter) continuously adjusts stimulus intensity until it is just detectable; threshold is the average of those settings across trials.
18
Q
What is the method of constant stimuli?
A
Present five to nine intensities in random order multiple times; plot percentage of detections against intensity; threshold is intensity detected on 50% of presentations.
19
Q
Which method for measuring absolute threshold is most accurate?
A
Method of constant stimuli.
20
Q
Which method for measuring absolute threshold is fastest?
A
Method of adjustment.
21
Q
How does the method of limits compare in accuracy and time requirements?
A
It is intermediate in both accuracy and time requirements.
22
Q
What is the difference threshold?
A
The smallest detectable difference between two stimuli.
23
Q
Who measured the difference threshold prior to Fechner?
A
Ernst Weber.
24
Q
What did Weber find about the difference threshold?
A
It increases proportionally with the magnitude of the standard stimulus.
25
What is Weber’s law?
The ratio of the difference threshold (ΔS) to the standard stimulus (S) is constant (K): ΔS/S = K.
26
How is the Weber fraction calculated?
K = ΔS / S.
27
In Weber’s weight example, what is K?
0.02, because 2 g/100 g = 4 g/200 g.
28
What is the Weber fraction for electric shock?
0.01.
29
What is the Weber fraction for lifted weight?
0.02.
30
What is the Weber fraction for sound intensity?
0.04.
31
What is the Weber fraction for light intensity?
0.08.
32
What is the Weber fraction for taste (salty)?
0.08.
33
How is the difference threshold determined experimentally?
Two stimuli (one standard, one comparison) are presented to blindfolded hands; the comparison weight is incrementally increased until the observer reports 'different'; DL is that difference.
34
What is the historical significance of Fechner’s and Weber’s work?
They established that mental processes can be measured quantitatively and that classical psychophysical techniques remain useful.
35
In what practical applications are classical psychophysical techniques used?
Prescribing corrective lenses (visual thresholds) and audiometric testing (hearing thresholds).
36
What is the purpose of magnitude estimation?
To measure how perceived intensity (e.g., loudness, brightness, shock) relates to physical stimulus intensity.
37
What is the procedure for magnitude estimation?
Observer is shown a reference stimulus assigned an arbitrary numerical value (e.g., 10); then views test stimuli of various intensities and assigns numbers proportional to perceived magnitude.
38
Give an example of magnitude estimation scaling.
If standard light is assigned 10, a light twice as bright gets 20; a light half as bright gets 5.
39
What are variations of magnitude estimation designs?
Some designs omit an explicit standard and rely on relative numerical ratings.
40
What is response compression?
When doubling stimulus intensity increases perceived magnitude by less than twofold (e.g., brightness).
41
What is response expansion?
When doubling stimulus intensity increases perceived magnitude by more than twofold (e.g., electric shock).
42
What is linear response?
When doubling physical stimulus intensity yields approximately double the perceived magnitude (e.g., line length).
43
What is Stevens’s power law?
P = K Sⁿ, where P is perceived magnitude, S is stimulus intensity, K is a constant, and n is an exponent determining compression, linearity, or expansion.
44
In Stevens’s power law, what does the exponent n represent?
Determines whether the response shows compression (n < 1), linearity (n ≈ 1), or expansion (n > 1).
45
Give an example calculation using Stevens’s power law with K = 1 and n = 2.
If S = 10, P = 1 × 10² = 100; if S = 20, P = 1 × 20² = 400, so doubling intensity yields a fourfold perceived increase.
46
How is the power function transformed into a straight line?
By taking logarithms of both P and S (log–log representation).
47
What does a slope less than 1 indicate on a log–log plot?
Response compression (e.g., brightness).
48
What does a slope approximately equal to 1 indicate on a log–log plot?
Linear response (e.g., line length).
49
What does a slope greater than 1 indicate on a log–log plot?
Response expansion (e.g., shock).
50
What is the functional significance of a low exponent (e.g., brightness n ≈ 0.6)?
Prevents overwhelming perceived differences when light levels vary enormously (indoors vs. sunlight).
51
What is the functional significance of a high exponent (e.g., shock n ≈ 3.5)?
Amplifies small increases in potentially harmful stimuli, prompting protective withdrawal.
52
What is a visual search task?
Observer locates a target stimulus among distractors as quickly as possible (e.g., finding a face in a crowd).
53
What does reaction time measure in a visual search task?
Time from stimulus onset to observer response; reveals processing mechanisms of attention and perception.
54
What are same–different judgments?
Observer decides whether two stimuli are identical or not.
55
What is perceptual matching?
Observer adjusts one stimulus (e.g., brightness, color) to match another.
56
What are action-based measures?
Observer closes eyes and walks to a remembered target location to assess perceived distance.
57
Why do classical threshold methods confound sensitivity and criterion?
Because they do not separate true ability to detect a stimulus (sensitivity) from a person’s tendency to say “yes” or “no” (response criterion).
58
What does Signal Detection Theory (SDT) separate?
Sensitivity from response criterion by including trials with and without the stimulus and analyzing responses in a contingency framework.
59
What is a hit in SDT?
Respond “yes” when the signal is present.
60
What is a miss in SDT?
Respond “no” when the signal is present.
61
What is a false alarm in SDT?
Respond “yes” when the signal is absent.
62
What is a correct rejection in SDT?
Respond “no” when the signal is absent.
63
Describe a basic SDT experiment structure.
Present a single low‐intensity tone on some trials and no tone on others in random order; observer responds “yes”/“no”; compute hit and false alarm rates.
64
How can response criterion be manipulated in SDT?
By changing payoffs (rewards/penalties) for hits, correct rejections, false alarms, and misses.
65
What is an ROC curve?
A plot of hit rate versus false‐alarm rate across different decision criteria.
66
How does sensitivity affect the shape of the ROC curve?
Greater sensitivity (larger d′) bows the ROC curve more sharply toward the upper-left corner; lower sensitivity makes it closer to the diagonal line.
67
What is d′ in SDT?
The distance between the means of the noise and signal+noise probability distributions; a measure of sensory sensitivity.
68
What is the decision criterion in SDT?
A cutoff on the perceptual‐effect axis; if the experienced value exceeds it, observer responds “yes,” otherwise “no.”
69
How do criterion shifts affect hit and false‐alarm rates?
A more liberal criterion increases both hit and false‐alarm rates; a more conservative criterion decreases both.
70
What is the key insight of Signal Detection Theory?
Criterion shifts move operating points along a given ROC curve without altering its shape, while changing d′ alters the ROC curve’s bowing.
71
What happens to the detection threshold when entering darkness?
It initially rises, then falls over time as vision improves, forming the dark-adaptation curve.
72
What is the dark-adaptation curve?
A graph showing how the detection threshold decreases moment by moment in darkness, indicating improving vision.
73
What assumption do classical psychophysical methods make when measuring functions like the spectral sensitivity curve?
They assume a stable response criterion throughout each experiment.
74
When is assuming a stable response criterion reasonable?
When stimulus properties (e.g., wavelength, frequency) change but motivational factors do not, and when using experienced, well-trained observers.
75
Under controlled conditions with stable criteria, are classical threshold methods still valid?
Yes, they remain a valid tool for mapping stimulus–perception relationships.
76
What is the psychometric function?
An S-shaped curve relating the percentage of “yes” responses (detection rate) to stimulus intensity, rising from near 0% at low intensities to near 100% at high intensities.
77
Which point on the psychometric function is used to define absolute threshold?
The 50% detection point.
78
Why was the staircase method developed?
To avoid wasting trials on stimulus levels far from threshold and to concentrate trials in the most informative, steepest part of the psychometric function near threshold.
79
What is the procedure for the staircase method?
Start with a clearly detectable or undetectable intensity; if the participant says “yes,” decrease intensity by one step; if “no,” increase by one step; continue the up-and-down sequence until enough reversal points occur, then average the intensities at reversals to estimate the threshold.
80
What are the advantages of the staircase method?
Efficiency, because it quickly homes in on the threshold region, and high data density near the true threshold, improving precision with fewer trials.
81
Give an example application of the staircase method.
In audiometry to construct audiograms: the procedure estimates absolute hearing thresholds across frequencies, showing that older adults typically require higher intensities than younger adults.
82
What is the Just Noticeable Difference (JND)?
The minimum intensity difference between two stimuli that allows an observer to reliably perceive them as different.
83
How is JND measured using the method of adjustment?
The observer adjusts the comparison stimulus until it is just noticeably brighter or darker than the standard, records that difference, repeats multiple times, and averages the differences to estimate the JND.
84
How is JND measured using the method of constant stimuli?
Present a fixed set of comparison intensities around the standard in random order; collect “comparison brighter” responses; plot a psychometric function (% “yes” vs. intensity); find intensities at 25% and 75%; compute JND as (I₇₅% − I₂₅%) / 2.
85
What does a steeper psychometric function slope indicate about the JND?
A steeper slope indicates a smaller JND, reflecting greater discriminability.
86
What is the staircase method for measuring JND?
Present a comparison stimulus each trial; if the observer says “yes” (difference detected), decrease comparison intensity by one step; if “no,” increase by one step; continue until enough reversals occur; estimate JND from the average difference at reversal points.
87
What does the psychometric function reflect in terms of neural responses?
It reflects how variability (noise) in neural responses causes detection probability to increase gradually with stimulus intensity, producing the S-shaped curve.
88
What is neural noise?
Random variability in neural firing rates across trials in response to a fixed stimulus.
89
How does tone intensity relate to neural response in SDT contexts?
As tone intensity increases, the average number of spikes in the auditory nerve increases, but the actual spike count varies due to neural noise; with no tone, baseline firing is around 7 spikes per trial.
90
How does the decision criterion function when using neural spike counts?
The observer sets a cutoff on spike count (e.g., say “yes” if spikes ≥ criterion); because of neural noise, the same tone intensity can sometimes produce spike counts below or above criterion, leading to hits, misses, false alarms, or correct rejections.
91
Why is the psychometric function S-shaped?
Because neural noise causes detection probability to rise gradually rather than abruptly as stimulus intensity increases.
92
What defines the absolute threshold in terms of the psychometric function?
The stimulus intensity at which the detection probability is 50%.
93
How does neural noise affect the absolute threshold?
Internal variability causes the threshold to vary, making the transition from non-detection to detection gradual rather than abrupt.
94
In SDT, what hit rate and false-alarm rate correspond to a decision criterion of N = 19 spikes?
Hit rate ≈ 0.80 and false-alarm rate ≈ 0.25.
95
What hit and false-alarm rates correspond to criteria of N = 16, N = 19, and N = 25 spikes?
For N = 16: hit ≈ 0.90, FA ≈ 0.42; for N = 19: hit ≈ 0.80, FA ≈ 0.25; for N = 25: hit ≈ 0.42, FA ≈ 0.05.
96
How do those (hit, FA) points relate to the ROC curve?
They trace out the ROC curve for that stimulus, showing how hit and false-alarm rates co-vary as the criterion shifts.
97
In SDT, what aspect of the ROC curve captures sensitivity?
The bowing or curvature of the ROC curve; greater bowing toward the upper-left indicates higher sensitivity.
98
In SDT, what does bias (criterion) affect?
It moves performance along a given ROC curve without changing the curve’s shape.
99
If a participant could produce a hit or miss but not a false alarm or correct rejection on a trial, was a signal presented?
Yes; hits and misses occur only on signal-present trials, so the presence of the possibility of hit or miss indicates a signal was presented.
100
Under what circumstances might a participant have a 100% hit rate and 0% false-alarm rate?
When the noise and signal+noise distributions do not overlap (extremely large d′) and the criterion lies in the gap between them, enabling perfect separation.
101
True or false: A lower decision criterion indicates a more conservative bias.
False; a lower criterion indicates a more liberal bias.
102
True or false: An ROC plot with multiple points on one curve illustrates criterion shifts, whereas multiple ROC curves illustrate different sensitivities.
True.
103
What does 'Miss' correspond to in terms of true/false positive/negative nomenclature?
Miss corresponds to a False Negative.
104
What does 'Correct Rejection' correspond to in terms of true/false positive/negative nomenclature?
Correct Rejection corresponds to a True Negative.
105
What does 'False Alarm' correspond to in terms of true/false positive/negative nomenclature?
False Alarm corresponds to a False Positive.
106
What does 'Hit' correspond to in terms of true/false positive/negative nomenclature?
Hit corresponds to a True Positive.
