ASA 125th Meeting Ottawa 1993 May

4pPP12. Critical bands for envelope cues.

Bruce G. Berg

Curt Southworth

Matthew Turner

Dept. of Cognitive Sci., Univ. of California, Irvine, CA 92717

Previous studies show that temporal envelopes can be used to discriminate complex sounds. This study estimates the effective bandwidth over which the auditory system extracts an envelope. Listeners discriminate a stimulus consisting of n, equal-intensity tones centered at 1000 Hz, from a stimulus with an intensity increment of the 1000-Hz tone. A roving level procedure is used to degrade absolute intensity cues, while variation of the digital-to-analog conversion rate degrades pitch cues. Theoretically, only envelope cues are preserved. Across conditions, tones are equally spaced with separations of 10, 20, 40, or 80 Hz. Within conditions, the number of tones varies from 3 to 41. Thresholds increase as the number of components increases until a certain bandwidth is reached, after which a ``Fletcher-type'' breakpoint is observed with thresholds either decreasing or remaining constant. For individuals, the bandwidth at the breakpoint is roughly the same across conditions. Sizable individual differences are found, ranging from a factor of 1.5 to 4 greater than critical bandwidths estimated from tone-in-noise detection tasks. A model based on the power spectrum of the envelope is evaluated. [Work supported by ONR.]