Neural Dynamics of Perceptual Order

How does the brain extract invariant properties of variable-rate speech? A neural model, called PHONET, is developed to explain aspects of this process and, along the way, data about perceptual context e ects. For example, in 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 consonant from /w/ to /b/ (Miller and Liberman, 1979). The frequency extent of the initial formant transitions of xed duration also in uences the percept (Schwab, Sawusch, and Nusbaum, 1981). PHONET quantitatively simulates over 98% of the variance in these data using a single set of parameters. The model also qualitatively explains many data about other perceptual context e ects. In the model, C and V inputs are ltered by parallel auditory streams that respond preferentially to transient and sustained properties of the acoustic signal before being stored in parallel working memories. A lateral inhibitory network of onsetand 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 rate in the sustained stream via a cross-stream automatic gain control interaction. The stored activities across these gain-controlled working memories provide a basis for rate-invariant perception, since the transient-to-sustained gain control tends to preserve the relative activities across the transient and sustained working memories as speech rate changes. Comparisons with alternative models tested suggest the t can not be attributed to the simplicity of the data. Brain analogs of model cell types are described.