Intermodal Competition and Compensation in Development

A large literature has attempted to verify experimentally the considerable anecdotal evidence that deprivation of input in one sensory modality leads to compensatory increases in the functioning of remaining modalities. Convincing evidence on this issue from convergent behavioral, physiological, and anatomical descriptions would provide information central to an understanding of how different brain systems become specialized to process different and specific types of information. Are there intrinsic properties of different brain regions that render them a suitable substrate to process certain and not other types of information? What is thc role of specific types of sensory input in the functional differentiation of specialized brain systems? The pertinent human literature on the effects of sensory deprivation consists almost entirely of behavioral studies, and these present a confusing array of results. Some studies report increases, some decreases, and others no differences in abilities of remaining modalities compared with those abilities in intact control subjects. This variability is no doubt due in large part to differences in the age of onset and completeness of blindness or deafness of the population under study. Additionally the etiology of the deafness or blindness is a key variable: For example, deafness secondary to encephalitis is likely to be associated with compromised functioning in several domains and thus make it difficult to separately assess the effects of the sensory deprivation per se. In the small number of studies that have controlled for these factors, there appears to be evidence for the hypothesis that elementary functions, like sensory thresholds and acuity within remaining modalities, may not display compensatory enhancement. In contrast, attentional processing and the spatial localization of information may show such enhancement (Burnstine, Greenough & Tees, 1984; Neville, 1988). Such behavioral data, if upheld, would raise specific hypotheses about the brain regions involved in intermodal compensation. For example, if major effects occur in attentional processing this would implicate nonprimary “association” areas