Neural dynamics of perceptual order and context effects for variable-rate speech syllables

How does the brain extract invariant properties of variable-rate speech? A neural model, called PHONET, is developed to explain aspects of this proces s and, along the way, data about perceptual context effects. For example, i n consonant-vowel (CV) syllables, such as /ba/ and /wa/, an increase in the duration of the vowel can cause a switch in the percept of the preceding c onsonant from /w/ to /b/ (J. L. Miller & Liberman, 1979). The frequency ext ent of the initial formant transitions of fixed duration also influences th e percept (Schwab, Sawusch, & Nusbaum, 1981). PHONET quantitatively simulat es over 98% of the variance in these data, using a single set of parameters . The model also qualitatively explains many data about other perceptual co ntext effects. in the model, C and V inputs are filtered by parallel audito ry streams that respond preferentially to the transient and sustained prope rties of the acoustic signal before being stored in parallel working memori es. A lateral inhibitory network of onset- and rate-sensitive cells in the transient channel extracts measures of frequency transition rate and extent . Greater activation of the transient stream can increase the processing ra te in the sustained stream via a cross-stream automatic gain control intera ction. The stored activities across these gain-controlled working memories provide a basis for rate-invariant perception, since the transient-to-susta ined gain control tends to preserve the relative activities across the tran sient and sustained working memories as speech rate changes. Comparisons wi th alternative models tested suggest that the fit cannot be attributed to t he simplicity of the data. Brain analogues of model cell types are describe d.