J. A. S. Kelso
Ctr. for Complex Systems, Florida Atlantic Univ., Boca Raton, FL 33431
Previous work [Tuller et al., JEP:HPP (in press)] revealed signature properties of nonlinear dynamical systems in how people categorize speech sounds. The data were modeled using a two-well potential function that deforms with stimulus properties and is sensitive to context. The model predicts an increase in the rate of change of the slope of the potential with increased repetitions of a percept. Thus the slope of the potential corresponding to a given physical stimulus should be steeper (and stability indexed by judged goodness should be greater) when the stimulus is presented at the end of a sequence than at the beginning. Similarly, the same physical stimulus presented near the middle of a sequence with few (or no) stimuli between them should show no such differences. In the present experiment stimuli from a ``say''--``stay'' continuum were presented sequentially with gap duration first increasing, then decreasing. The eight S's had to identify each token and to rate how good an exemplar it was of the perceived category. Results confirmed model predictions, further supporting the hypothesis of a context-sensitive dynamical representation underlying speech.