Lecture 6: Psychophysics and Signal Detection Theory

What is the brain behavior quantification system similar to?

radar

What are the 2 types of commonly used psychometric functions?

Absolute threshold measurement (a detection task)

Relative threshold measurement (a discrimination task)

What is an example of absolute threshold measurement? How would the graph look?

to determine whether a light flash is seen on a computer screen

The proportion of ”seen" responses is plotted on the y-axis and the physical

parameter on the x-axis.

How to design an absolute threshold experiment?

Take different samples at diffferent magnitudes. Demonstrate them to subjects randomly, and judge response. Do not use a gradient of stimuli, as it may condition a subject to be waiting for a response, possibly leading to inaccuracies.

What is psychophysics?

Psychophysics is the scientific discipline that

explores the connection between physical stimuli and

subjective responses.

What is a psychometric function?

Psychometric Function provides the fundamental data for psychophysics. It relates the subject’s response to the physical stimulus and is used to quantitatively measure behaviors. Its abscissa (x-axis) plots the physical parameter of a stimulus and the ordinate (y-axis) plots the observer’s response.

What is an example of relative threshold measurement? How would the graph look?

to determine if two sounds heard are the same or different (also referred to as “Two-alternative forced choice (2AFC)” paradigm)

The percentage of correct responses (or a similar value) is plotted on the y-axis and the physical parameter on the x-axis.

Psychometric functions can also measure ____ _____

stimulus sensitivity (right means less sensitive, left means more sensitive)

What is the discriminability index (d’)

A measure to quantify the discriminability of a stimulus independent of the criterion an observer adopts

What is signal detection theory?

A mathematical theory to analyze an observer’s decision in detecting or discriminating two (or multiple) random variables

Explain signal detection theory using an example.

What is the receiving operating characteristic? (ROC)

An analytic method to quantify an observer’s decision (Hits v.s. False Alarms)