THE NONLINEAR DYNAMICS OF SPEECH CATEGORIZATION

Little is known about the processes underlying the nonlinear relations hip between acoustics and speech perception. In Experiment 1, we explo red the effects of systematic variation of a single acoustic parameter (silent gap duration between a natural utterance of a and a synthetic vowel ay) on judgments of speech category The resulting shifts in cat egory boundary between say and stay showed rich dynamics, including hy steresis, contrast, and critical boundary effects. We propose a dynami cal model to account for the observed patterns. Experiment 2 evaluated one prediction of the model, that changing the relative stability of the two percepts allows categorical switching. In agreement with the m odel, an increase in the number of stimulus repetitions maximized the frequency of judgments of category change near the boundary. Thus, a d ynamical approach affords the rudiments for a theory of the effects of temporal context on speech categorization.