1 Psychophysics and Psychoacoustics. 2 Yes, there is a difference Psychophysics: The scientific study of the relation between physical events and the.

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Psychophysics and Psychoacoustics

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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.

• 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.

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Psychophysical Laws

Physical quantity PerceptionIntensity Loudness

Frequency Pitch

Sensitivity (or detectability) vs. Response Proclivity

The difference between what you hear and what you say you hear.

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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

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Classic Measurement Methods

• Method of Limits

• Method of Adjustment

• Method of Constant Stimuli

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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).

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Method of Limits

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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.

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Method of Limits

• Need to determine…– High transition point– Low transition point– Point of subjective equality

• See next slide for example

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Method of Limits

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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.

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Modified Method of Limits

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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

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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.

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Method of Constant Stimuli

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A Few Practice Problems

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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.

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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).

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• 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.

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QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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• Examples on next slide…– High intensity yes bias– High intensity no bias– Low intensity yes bias– Low intensity no bias

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• 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.

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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.

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Summary

1 Psychophysics and Psychoacoustics. 2 Yes, there is a difference Psychophysics: The scientific study of the relation between physical events and the.

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