Neurobiological Basis of Speech: A Case for the Preeminence of Temporal Processing

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Abstract
In this paper we present evidence supporting the hypothesis that a basic temporal processing impairment in language-impaired children underlies their inability to integrate sensory information that converges in rapid succession in the central nervous system. We provide data showing that this deficit is pansensory; that is, affects processing in multiple sensory modalities, and also affects motor output within the millisecond time frame. We also provide data that links these basic temporal integration deficits to specific patterns of speech perception and speech production deficits in language-impaired children. We suggest that these basic temporal deficits cause a cascade of effects starting with disruption of the normal development of an otherwise effective and efficient phonological system. We propose further that these phonological processing deficits result in subsequent failure to learn to speak and to read normally. That is, both the language and reading problems have their basis in deficiently established phonological processing and decoding. Finally we use data derived from our ongoing behavioral studies with language-impaired children to address some fundamental issues pertaining to the neurobiological basis of speech perception and production (e.g., hemispheric specialization) underlying these processes. We suggest that results from magnetic resonance imaging (MRI) and positron emission tomography (PET) studies, as well as studies of behavioral performance in normal adults and adults with acquired lesions, combined with more recent results from animal studies, all support the view that a left-hemispheric specialization for speech initially developed through evolution as a specialization for processing and producing sensory and motor events that occur in rapid succession.