Language development: a sensory development and signal processing perspective.

Abstract

The relationship between the development of sensory mechanisms and the maturation of language behavior is poorly understood. From the outset it is important to distinguish between what is necessary for the development of any language system versus what is involved in the development of the verbal language system in the unimpaired child. The presence of highly sophisticated language systems among persons who communicate manually reminds us that no single source of sensory information is absolutely required for the development of at least some form of language system. Nevertheless, there persists a general belief that the availability of an accurate representation of the acoustic environment will facilitate at least the normal process of language acquisition. A more tenable question is whether the completeness or accuracy of the sensory representation places limitations on the emergence of language comprehension and production. I think this is unlikely, unless the relatively untested area of the maturation of "nonlinear processing mechanisms" provides information different than that obtained from more traditional linear systems analysis approaches. The relative integrity of the language systems of the hearing impaired, despite very dramatic differences in auditory sensitivity and frequency-resolving power, argues strongly that whatever mechanisms account for language organization are relatively immune to significant alterations in sensory input. Caution must be exercised here, however, since these comments generally refer to the outcome of studies performed on persons with acquired hearing loss. Naturalistic or descriptive studies of patients with congenital hearing loss are always susceptible to the criticism that whatever agent or agents produced the sensory impairment may also have produced concomitant impairment of nonsensory mechanisms. Nevertheless, comparisons of young infants and hearing-impaired adults, with respect to behavioral studies, suggest that there is a sufficiently rich sensory representation of the acoustic environment to permit the development of language skills much earlier than they naturally emerge. Electrophysiologic comparisons of human newborns and adults also suggest that the diminished auditory sensitivity and alterations in the frequency contour of sensitivity are insufficient to explain age differences in language comprehension and production performance. It may well be that the brain mechanisms responsible for the establishment of language behavior are sufficiently flexible to accommodate even a greatly impoverished sensory representation.(ABSTRACT TRUNCATED AT 400 WORDS)