Advances in Cognition, Education, and Deafness

Cortical Organization and Information Processing in Deaf Children

Cortical Organization and Information Processing in Deaf Children Carol A. Kusche Mark T. Greenberg In order to develop a neurolinguistic model for cortical processing during reading, we collected data on 24 deaf children to support the following two hypotheses that several researchers, including ourselves, have proposed (Greenberg & Kusche 1989; Kusche 1985; Neville 1985). 1. Due to auditory deprivation, prelingual deafness may result in differences in the organization or reorganization ofthe brain as compared to that of individuals with normal hearing. These differences are believed to be reflected in aspects of functioning such as short-term memory and reading ability. 2. Differences in information-processing abilities among subgroups of deaf children may be related to differences between these groups in cortical organization and functioning. A NEUROLINGUISTIC MODEL OF PROCESSING DURING READING Our proposed neurolinguistic model of cortical processing during reading is based upon models proposed by Geschwind (1979) and Hynd (1986). We embellished upon these models, however, because they provided only partial descriptions and did not take into account certain processes that are necessary for reading. As noted by Kolb and Whishaw (1985), "A comprehensive model of language function must incorporate stimulation and lesion data and include subcortical struc243 244 Neuroscientific Issues Amygdala & Hippocampus l+ Amygdala & Hippocampus Area 17L & R --+ Areas 18, 19L & R --+ Area 39L & R --+ Area 22L --+ Area 44L --+ Face Area L --+ Area 40L --+ Areas 21 L & R --+ amygdala, hippocampus, frontal lobes ~ feedback from frontal lobes FIGURE 1 A proposed neurolinguistic model of cortical processing during normal reading. tures as well as mechanisms of affective control. Such a model remains to be proposed" (p. 528). Our model was developed first by reviewing the types of procedures that are utilized while reading. We then matched these processes to the corresponding areas of the brain (based on Brodmann's 1909 paradigm) that are believed to subserve these functions. (For a more comprehensive review, the reader is referred to Kolb and Whishaw 1985, and to the complete version of this paper), Finally, Cortical Organization and Information Processing in Deaf Children 245 we drew a "map" to illustrate the sequential processing involved among these areas. As can be seen in Figure 1, we proposed that information is relayed from the primary visual cortex (area 17) to the secondary visual cortex (areas 18/19) in both hemispheres, resulting in information from the retinal projections becoming interpreted as letters and perhaps words. From the secondary visual cortex, information proceeds to the angular gyrus (39) in both hemispheres, where visual short-term memory and spatial/location processing can be undertaken. Grapheme -to-phoneme translation and order-retention are then processed in Wernicke 's Area (22) in the left hemisphere, and speech-motor programming and perhaps grammatical processing are undertaken in Broca's Area (44), again in the left hemisphere. From there the information is relayed to the left face area for subvocal phonetic processing, to the supramarginal gyrus (40) in the left hemisphere for phonetic short-term memory processing, and to area 21 in both hemispheres for long-term memory encoding, to the amygdala for affective associations , and to the frontal areas for associative processing. Information from the frontal lobes is then fed back to various regions of the brain. Obviously, this process is very complex, involving numerous areas of the brain working in intricate coordination. To add to the complexity, it should be noted that although this model is presented as sequential, the brain is actually processing different units of information simultaneously and is continually integrating these units. We would also expect to find individual differences in reading processing within any large population, so that this model represents only an "average" reading model. We believe that our reading model might prove useful in deafness research with regard to examining the cortical processing of subgroups of deaf subjects. For example, specific types of reading difficulties might be expected to be found with different types of processing. It might also be found that certain processing strengths are substituted for weaker areas (e.g., a visual-gestalt word-recognition function might be utilized in lieu of phonetic encoding, episodic memory might be used to compensate for poor verbal short-term memory, etc.). This model might be especially useful if used in conjunction with paradigms from neurological research (e.g., EEG studies) as well as from neuropsychological research. The model could have useful implications for educational interventions. INFORMATION PROCESSING IN 24 DEAF CHILDREN Subjects The sample originally studied included approximately 50...