Advances in Cognition, Education, and Deafness

Analysis

Analysis Anthony B. Walff As cognitive science and neuroscience grow closer together, there has been a gradual increase in research on neurological and neuropsychological aspects of deafness. Such work is motivated by a number of questions, including 1. What is the effect of congenital deafness on brain development and/ or function? 2. Are particular educational strategies suggested by observed patterns of cerebral function or cognitive function in deaf students? 3. Are there general principles of cognitive or neurological development that can be learned from studying these phenomena in deaf subjects? To a greater or lesser degree, each of the four papers in this chapter has addressed one or more of these issues. It should be noted at the outset that none of the work reviewed here utilized physiological measurements. Two of these papers, those by Craig and Gordon and by Kusche and Greenberg, do report cognitive findings that provide at least a speculative functional view of some underlying neural mechanisms. The paper by Knobloch-Gala presents no data but instead discusses certain formal linguistic incongruities in some educational practices for deaf learners that may in turn conflict with the author's view of underlying neural organization. MacTurk and Trimm present interesting infant data that is not particularly germane to the understanding of neurological issues, but is quite relevant to questions of compensatory processes. Craig and Gordon have now established a record of careful, systematic re258 Analysis 259 search that suggests the existence of some degree of cerebral reorganization, associated with specialized cognitive functioning, among their deaf subjects. Most notably, using Gordon's Cognitive Laterality Battery, they have demonstrated a superiority of deaf subjects over hearing subjects on certain purely visuospatial tasks. They also argue that the lower performance of deaf subjects on verbosequential portions of their battery reflects a processing difficulty that is inherent in deafness. Taken at face value, this pattern of relative weakness for verbosequential processes, and relative strength for visuospatial functioning, is suggeitive of a pattern of atypical cerebral asymmetry that classically favors right hemispheric processes. Although one may question the validity of virtually any nonsign -based linguistic assessment procedure with deaf subjects (even when the instructions are signed, as they were in this case), the verbosequential tasks used here were quite free of syntactic demands, and only one involved a semantic process (categorical retrieval of lexical items). In any case, these possible objections do not negate the affirmative finding of enhanced spatial functioning among deaf subjects. These findings are also consistent with results reported by other laboratories, using both behavioral methods (Marcotte & LaBarba 1987) and electrophysiological methods (Wolff & Thatcher 1990), which have demonstrated cortical reorganization and enhanced right hemispheric functioning in deaf subjects . In their paper, Kusche and Greenberg provide a restatement of the view that deafness may give rise to cerebral reorganization. They offer a theoretical model of the process of reading, which is not directly referenced in, and seems unrelated to, the later data-oriented portion of their article. However, a well-taken point in their speculative exposition is that the process of reading must involve numerous cortical areas. This view is not controversial and is consistent with the contemporary view of all complex human behaviors. It follows that cortical reorganization or functional alteration in anyone or a combination of the relevant "modules " may give rise to modifications in the process of reading (or other complex behavior). The animal sensory deprivation literature reveals that early deafferentation (removal or attenuation of sensory input), as well as environmental enrichment, can give rise to a host of modifications in cortical and subcortical cytoarchitectonics , neurochemistry, and behavior (e.g., Gyllensten, Malmfors & Norrlin 1966; LeVay, Wiesel & Hubel1980; Rubel 1984; see also Renner & Rosenzweig 1987 for a general review of environmental effects on brain structure and function). There is no logical reason to doubt that auditory deafferentation in the developing human should lead to similar developmental effects in the cerebral cortex. Further, given the multiplicity of neural connections to primary and secondary auditory cortex, there are numerous possible areas and modules that may be affected secondarily by the absence of auditory stimulation. This effect may result in altered functioning in virtually any cognitive domain, for example, memory , executive control, or sequencing. The data offered by Kusche and Greenberg, although not clearly related to their speculative treatment of reading, do reflect the presence of some aspects of cognitive functioning that are not typical of hearing subjects. For example, despite above-average WISC-R Performance scores, one of their high-functioning groups...