CHAPTER 10

Auditory Sensitivity

PSYCHOACOUSTICS

• A branch of psychophysics

The study of the relation between: • the physical aspects of sound

and • the psychological experience of sound

Threshold or Limen

• Absolute Threshold -- lowest value of stimulus which can be detected

• Difference Threshold -- smallest detectable change in a stimulus

• These 2 Thresholds were the primary questions in CLASSICAL PSYCHOPHYSICS

Thresholds

Minimum Audibility Curve--

• Plot of threshold of detection (in dB SPL) as a function of frequency

• Lowest thresholds in 1 to 4 kHz region

Thresholds

The Auditory Response Area

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Auditory Response Area

• Range of useable hearing-- from threshold of detection to threshold of feeling/pain

• Also called the DYNAMIC RANGE OF HEARING

Thresholds

Differential Sensitivity

• Detecting changes in a stimulus

• (e.g., how small a change in frequency can you detect)

• Measured as the jnd - just noticeable difference

Diff. Sensitivity//Weber’s Law

Weber’s Law--A Theory of human differential sensitivity

• Δ S/S = k

• Size of jnd = constant fraction of the stimulus you start with

• It’s easier to detect small changes in a stimulus if it had a small value to begin with.

Diff. Sensitivity//Weber’s Law

Frequency Resolution

• The Critical Band reflects “internal filtering”--the ability to attend to a narrow range of frequencies

• Remember the tuning curves from Bekesy’s dead ear and the healthy cochlea?

• You need the healthy cochlea to have good frequency resolving power

Good Frequency Resolution Allows you to:

• Listen to harmonic structure of complex signals

• Detect Shifts in Frequency (esp. formant transitions)

• Hear and Understand signals in noise

Brief Sounds: Temporal Integration

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Temporal Aspects: TEMPORAL INTEGRATION

• A certain amount of energy must be present for detection of a brief signal.

• The process of summing energy over time is called integration and it is completed by 300 ms.

• If the signal is shorter than 300 ms, then power must be increased for the signal to be detected.

Temporal Integration