Connectionists: laminar cortical dynamics of conscious speech perception

[Stephen Grossberg]

The following article can be found at http://cns.bu.edu/~steve . It proposes how the the brain can complete conscious representations of speech in noise using future contextual information and, more generally, how the laminar circuits of neocortex may realize different types of biological intelligence. Previous articles on the web page have proposed how variants of these laminar circuits can achieve 3D vision and figure-ground separation, and cognitive working memory and chunking of sequential lists. The shared design of these circuits begins to show how multiple cortical areas can communicate in a self-consistent way to achieve visual and auditory perception and cognition.

Laminar cortical dynamics of conscious speech perception: 
A neural model of phonemic restoration using subsequent context in noise
Grossberg, S. and Kazerounian, S.

Abstract: 
How are laminar circuits of neocortex organized to generate conscious speech and language percepts? How does the brain restore information that is occluded by noise, or absent from an acoustic signal, by integrating contextual information over many milliseconds to disambiguate noise-occluded acoustical signals? How are speech and language heard in the correct temporal order, despite the influence of contexts that may occur many milliseconds before or after each perceived word? A neural model describes key mechanisms in forming conscious speech percepts, and quantitatively simulates a critical example of contextual disambiguation of speech and language; namely, phonemic restoration. Here, a phoneme deleted from a speech stream is perceptually restored when it is replaced by broadband noise, even when the disambiguating context occurs after the phoneme was presented. The model describes how the laminar circuits within a hierarchy of cortical processing stages may interact to generate a conscious speech percept that is embodied by a resonant wave of activation that occurs between acoustic features, acoustic item chunks, and list chunks. Chunk-mediated gating allows speech to be heard in the correct temporal order, even when what is heard depends upon future context.

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