Pyschophyical methodology Flashcards
Definition of threshold
The point at which a physiological effect begins to be produced
What is detection
Is something there
What is discrimination
Change in supra-threshold stimulus
What factors affect threshold
Intrinsic noise
Observer criterion
Extrinsic noise
Intrinsic noise
Spontaneous neural activity
Observer criterion
How much physical change is required before the subject is comfortable accepting an event occured
Extrinsic noise
Fluctuation of the number of photons of light that reach the retina from the stimulus
What can only be minimized during threshold testing?
Objective criterion
What are the pyschophysical methods of measuring a threshold
Limits Adjustment Staircase Constant stimulus Forced-choice
Ascending limits
Stimulus intensity is gradually increased in each successive presentation until the patient reports detection
Descending limts
Stimulus intensity is gradually decreased in each successive presentation until the patient reports they can barely see it
Method of adjustment
Subject has complete control of the rate and magnitude of stimulus itnensity change
Ascending staircase
Sub-threshold presented until detection, then decrease light until reversal, repeat
Descending stiarcase
Supra-threshold presented, decreased until reversal of response, repeat
Constant stimulus
Fixed range of stimulus values used and presented repeatedly in random order
Subject must determine detection or if one is greater than a standard
What is threshold in the constant stimulus detection?
Stimulus value that coincides with 50% correct
What is threshold in constant stimulus discrmination?
Stimulus interval between 84% adn 50% correct
Point of subjective equality
50% point for discrimination when subject does not perceive change in stimulus value
What makes forced-choise different?
Subject is forced to make a positive response regardless of whether the stimulus is seen
What is the preferred pyschophysical method?
Forced-choice
Where does the 2 alternative psychometric function begin?
50%
Where is the threshold in a 2 alternative forcced choice?
at the 75% correct stimulus intensity
Where does the 4 alternative psychometric function begin?
25%
Where is the threshold in a 4 alternative forced choice?
62.5% correct stimulus intensity
How do you calculate the guess rate?
1/number of choices
What does the signal detection theory do?
Estimate the effects of observer sensitivity and observer bias
What is the discriminability index?
Measure of the separation between noise and signal plus noise distributions
How do you calculate the discriminability index?
Separation divided by spread
What is separation?
difference between the means of the noise and S+N distributions
What is spread?
standard deviation of the distributions
What does a higher discriminability index mean?
Less of an overlap and an easier to detect stimulus
Strict criterion
Large change in internal response must occur for a subject to report that they detect the stimulus
Laxed criterion
Subject is willing to accept that the smallest change in internal response that they detect as being different must mean that a stimulus was present
Who has a higher threshold?
Strict
Who’s criterion line will intersect a larger proportion of the noise only distribution?
Laxed
Who attempts to maximize the times they are correct?
Laxed
Who attempts to minimize the times they are incorrect?
Strict
False positive
Responding yes when there isnt a stimulus
Hits
Responding yes when there is a stimulus
False negatives
responding no when there is a stimulus
Rejections
Responding no when there is not stimulus
Pay-off matrix
Attempt to influencee subject’s criterion to force subject to tend toward strict or laxed
Weber’s law
Threshld to detect a stimulus will vary proportionally with the magnitude of the stimulus itself
Fechner’s law
Proposed that a stimulus magnitude produces the same unit change in the internal perceptual response
Steven’s power law
Magnitude of the perceptual experience varies with a power law of the physcial stimulus magnitude
Magnitude estimation
Subject trained to use a scale to quantify the magnitude of their perceptual experience
