LECTURE 14.2


PSYCHOPHYSICS

I. The goal of Fechner's psychophysics: To find the relationship between physical reality and subjective reality (relationship between mind and matter)

A. Measure the mind

B. Without bias

C. Systematically

D. Repeat observations

II. How (For the absolute threshold or absolute limen)

A. Present stimuli in ascending order

B. Find point at which 50% of time detect stimulus, 50% of time, fail to detect

C. Present stimuli in descending order. Note: Beginning of counterbalancing to deal with order effects

D. Find point at which 50% of time detect stimulus, 50% of time, fail to detect

E. Determine absolute threshold by averaging the two points (50% detection in ascending order, 50% detection in descending order). Note: Beginning of use of average in psychology, realizing that any given response may be affected by random error, but that random errors will sum to zero over the long run.

III. Signal detection theory

A. Threshold = the actual sensation (d') and the decision to report the sensation (beta). Two people may experience the same sensation but one may say they heard the tone, the other, being a more cautious sort, may not report hearing the tone.

B. Have trials where present stimulus and trials where don't present stimulus. When subject reports stimulus and it was present, it's a "hit." When subject reports stimulus and it wasn't presented, it's a "miss."

C. Plotting hits as a function of false alarms to get the response operating characteristic (ROC): a measure of how conservative or liberal a person is in reporting the presence of a stimulus

1. The distance between the signal and noise distributions equals d' (sensitivity)

2. The slope of the ROC is beta (criteria)

Signal Detection Tutorial


Lecture 14.3

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