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The nonlinear dynamics of temporal
categorization. Jean-Claude Darcheville & Céline Clement Université de Lille, Ch. de Gaulle, France Previous works had revealed signature properties of nonlinear dynamical systems in speech categorization in human (Tuller, Case, Ding, Kelso, 1994). Using a paradigm developed by these authors, we explored the effects of systematic variation of a temporal parameter. The question is to establish in four adult humans a discrimination between two stimuli - S1 and S2 - along the temporal dimension. The discrimination between S1 and S2 is studied under three conditions : two involves sequential presentation of stimuli that change from S1 to S2 and from S2 to S1, and one involves the random presentation of the stimuli (the duration of the presentation of a circle on the screen of a computer). In the sequential presentation, the resulting shifts in category boundary between the 0,2 s. and 2,10 s. durations showed rich dynamics, including hysteresis, contrast and critical boundary effects. Hysterisis as multistability characterizes the nonlinear dynamics of the system. These dynamical properties tend to confirm the hypothesis that there's no time representation. This allow to wonder about the relevance of the concept of internal clock. Keywords: human, nonlinear dynamics, categorization, hysterisis, timing, reinforcement contingencies, internal clock |
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