Psychophysics and Psychoacoustics

Yes, there is a difference Psychophysics: The scientific study of the relation between physical events and the sensations they give rise to. Psychoacoustics: The area of psychophysics that focus on the perception of sound.

Psychophysical Laws Physical quantity Perception Intensity Loudness Frequency Pitch Sensitivity (or detectability) vs. Response Proclivity The difference between what you hear and what you say you hear.

Background Background Absolute threshold or absolute limen Smallest stimulus that a person can detect. Difference threshold or difference limen Smallest difference that a person can detect between two stimuli

Classic Measurement Methods Method of Limits Method of Adjustment Method of Constant Stimuli

Method of Limits The experimenter has control of the stimulus and the subject responds after each trial. The point between the yes-no responses is known as the transition. You need to average the transitions to determine threshold. Example on next slide is for absolute limen (threshold).

Method of Limits

Method of Limits Method of Limits for Difference Limen. Goal of this method is to … match a probe or test stimulus with a reference stimulus. Determine the least noticeable difference between a probe and a reference.

Method of Limits Need to determine… See next slide for example High transition point Low transition point Point of subjective equality See next slide for example

Method of Limits

Modified Method of Limits Uses bracketing (stairstep) to determine threshold. Can be more efficient. Numerous applications. e.g., audiometric threshold. See next slide for example.

Modified Method of Limits

Method of Adjustment Similar to method of limits except that the the stimulus is constantly varied and the subject controls the stimulus. E.g., Bekesy Audiometry

Method of Constant Stimuli Stimulus level is randomized. Psychometric function (PF) is generated based on percent of time the stimulus is correctly identified. Threshold is A predetermined point in PF. usually 50% or 75%. Common Application is PI-PB function.

Method of Constant Stimuli

A Few Practice Problems

Problems with classical methods Method of limits and adjustment are susceptible to yes (aggressive) or no (passive) bias. Method of constant stimuli can identify yes bias by using catch trials, but is still susceptible to no bias.

Theory of Signal Detection (TSD) Three things can affect our ability to detect a signal. External noise Internal noise Internal response Using TSD we can control for internal response (bias).

Theory of Signal Detection (TSD) TSD provides a measure of detectability (d’) that is free from response bias. d’ is the measure of strength of signal relative to noise. Response bias (β): individual influence on response.

Theory of Signal Detection (TSD)

Theory of Signal Detection (TSD) Examples on next slide… High intensity yes bias High intensity no bias Low intensity yes bias Low intensity no bias

Theory of Signal Detection (TSD) Whenever the hits exceed the number of false alarms (FAs), the listener can theoretically detect the signal. Threshold is the lowest intensity or level where the hits exceed the FAs. When hits are about the same as the FAs, the person is guessing and can not detect the signal.

Theory of Signal Detection (TSD)

Theory of Signal Detection (TSD)

Theory of Signal Detection (TSD)

Theory of Signal Detection (TSD)

Other Measurement Methods Magnitude Estimation Subject estimates magnitude of the stimulus Ratio Comparison Subject perceives a ratio between two stimuli Cross-modality matching Matches magnitude between two stimuli. e.g., visual, auditory, somatosensory, olfactory, or shock. Both magnitude estimation and ratio comparison have been used to measure the growth of loudness and pitch.

Summary