ASA 124th Meeting New Orleans 1992 October

4aSP5. Evidence for bistability in the region of perceptual boundaries.

Pamela Case

Betty Tuller

J. A. S. Kelso

Mingzhou Ding

Ctr. for Complex Systems, Florida Atlantic Univ., Boca Raton, FL 33431

Examples of the nonlinear relationship between acoustics and speech perception abound in the literature, most notably in the investigations of categorical perception. However, the dynamics of this relationship have been virtually ignored. In previous work, it has been reported that systematic variation of a single acoustic parameter in an identification task revealed evidence of signature properties of nonlinear dynamical systems including hysteresis effects and bistability [Tuller et al., J. Acoust. Soc. Am. 89, 1997 (A) (1991)]. In the present work, the relative stability of the alternative percepts is explored by manipulating the number of stimulus repetitions. Near the perceptual boundary, an increased number of stimulus repetitions maximized the frequency of observed spontaneous changes in perception. This suggests that perceptual change with sequential variation of an acoustic parameter results from loss of stability of the original percept. Thus perceptual dynamics, not solely acoustic stimulus information, determines perception of speech categories. [Work supported by NIDCD and NIMH.]