## 4pPP19. Estimates of spectral weights and internal noise in the discrimination of spectral variance.

### Session: Thursday Afternoon, May 16

**Author: Robert A. Lutfi**

**Author: Eunmi Oh (Dept. of Communicative Disorders**

**Location: Univ. of Wisconsin, Madison, WI 53706**

**Abstract:**

An experiment was conducted to measure the relative contribution of
spectral weights and internal noise in the discrimination of spectral variance.
The stimuli were simultaneous tone complexes comprised of the six octave
frequencies from 250 to 8000 Hz. On each presentation the levels of components
in dB were drawn independently and at random from one of two normal
distributions having identical means but different variances ((sigma)[inf N] = 1
dB, (sigma)[inf S] = 2--10 dB). In the standard 2IFC procedure, the listener's
task was to choose the complex having the greater variance in component level.
The shape of the psychometric function for all five listeners was markedly
different from that of an observer limited only by additive internal noise. It
was consistent with an observer that gives weight to only one or two components
in the complex. This result, however, was inconsistent with the weighting
functions computed from the trial-by-trial data from these listeners. Both
measures can be reconciled if it is assumed that listener weights vary from
trial to trial, or equivalently that observations are corrupted by
multiplicative rather than additive internal noise. [Work supported by NIDCD RO1
DC01262-04.]

from ASA 131st Meeting, Indianapolis, May 1996