neural dynamics of speech perception and word recognition

[Stephen Grossberg]

The following article is available at
http://www.cns.bu.edu/Profiles/Grossberg in PDF and G'zipped
Postscript versions.

Grossberg, S. and Myers, C.W. (2000). The resonant dynamics of speech
perception: Interword integration and duration-dependent backward effects.
Psychological Review, in press.

ABSTRACT: How do listeners integrate temporally distributed phonemic
information into coherent representations of syllables and words?  During
fluent speech perception, variations in the durations of speech sounds and
silent pauses can produce different perceived groupings.  For example,
increasing the silence interval between the words "gray chip" may result in
the percept "great chip", whereas increasing the duration of fricative
noise in "chip" may alter the percept to "great ship" (Repp et al., 1978).
The ARTWORD neural model quantitatively simulates such context-sensitive
speech data.  In ARTWORD, sequential activation and storage of phonemic
items in working memory provides bottom-up input to unitized
representations, or list chunks, that group together sequences of items of
variable length.  The list chunks compete with each other as they
dynamically integrate this bottom-up information.  The winning groupings
feed back to provide top-down support to their phonemic items.  Feedback
stablishes a resonance which temporarily boosts the activation levels of
selected items and chunks, thereby creating an emergent conscious percept.
Because the resonance evolves more slowly than working memory activation,
it can be influenced by information presented after relatively long
intervening silence intervals.  The same phonemic input can hereby yield
different groupings depending on its arrival time.  Processes of resonant
transfer and competitive teaming help determine which
groupings win the competition.  Habituating levels of neurotransmitter
along the pathways that sustain the resonant feedback lead to a resonant
collapse that permits the formation of subsequent resonances.