Cognition, Education, and Deafness: Directions for Research and Instruction

Cognitive Processing and Language in Deaf Students: A Decade of Research

Cognitive Processing and Language in Deaf Students: A Decade of Research Michael Rodda George Buranyi Ceinwen Cumming Beverly Muendel-Atherstone Despite intensive educational efforts, it is not uncommon for deaf students to lag behind hearing peers in the acquisition of verbal language and academic skills. Available neuropsychological research provides conclusive evidence for the reasons for this phenomenon. One problem is that variables such as age of onset of deafness, etiology, degree of hearing loss, amount of language before hearing loss occurred, and educational treatment are not usually controlled, and they exert a significant effect on the results obtained (Kelly & Tomlinson-Keasey, 1978). Nevertheless, a number of suggestions are possible, and these will be considered in some detail in the remainder of this paper. Differential Hemispheric Specialization and ~emory Strategies Studies of commissurotomized patients (i.e., patients who have surgically divided forebrain commissures), despite being open to criticism, have provided valuable information on hemispheric specialization in the brain and have produced some fairly consistent findings. Research with these patients indicates that, in addition to left-hemispheric dominance in language skills and right-hemispheric dominance in visual-spatial skills, the left hemisphere may be more specialized for analytical processing and the right hemisphere for gestalt processing (Bogen, 1969; Nebes, 1974; Sperry, 1973). In particular, studies of this type appear to demonstrate that the right hemisphere of commissurotomized patients is superior in generating a complete stimulus configuration from partial or fragmentary information (Nebes, 1971, 1972, 1973, 1974). However, the right hemisphere is not totally nonverbal, and it does playa vital role in the recovery of speech and language functioning in cases where the left hemisphere has been damaged or is malfunctioning (Searleman, 1977; see Kusche, pp. 115-120). Evidence concerning cerebral specialization has also been obtained from neurologically abnormal deaf subjects. Not surprisingly, lateralization of language functions has been the focus of much of this research. Kimura (1976), in examining seven cases of deaf aphasia cited in the literature, noted an association of manual communication disorder (sign language) with lefthemisphere control of complex motor behavior rather than of language. The analysis of McKeever, Hoemann, Florian, and Van Deuenter (1976) supports this hypothesis; they conclude that such patients may be demonstrating motor skill deficits rather than aphasia. Kimura, Battison, and Lubert (1976) The complete version of this paper is available in microfiche or hard copy from ERIC Document Reproduction Service. Ask for Document No. ED 170 066. 94 provided additional support for such an explanation when they stated: "It is quite possible that the degree of impairment seen in our subject on the linguistic hand movements parallels that of the nonlinguistic-that is, his defect is primarily one of motor sequencing" (p. 571). Recent research involving neurologically normal hearing-impaired subjects has been illuminating on hemispheric specialization in such individuals . Employing tachistoscopic presentation of verbal and nonverbal stimuli to the visual hemifields (left or right half of the visual field), Phippard (1977) found that a group of deaf subjects taught by oral methods had a right-hemisphere advantage in perceiving both verbal and nonverbal material . A group of subjects taught by a combination of oral and manual techniques showed no evidence of later<:.lization. The results of McKeever, Hoemann , Florian, and Van Deuenter (1976) indicated that when stimuli are bilaterally presented, deaf subjects show minimal hemifield asymmetry for both English words and ASL stimuli. With unilateral presentation, deaf subjects showed a left-hemisphere advantage for the recognition of words. In discussing their results, these authors suggested that as the task becomes more complicated, there is less dominance in one hemisphere in deaf subjects . However, Wilson (1977) suggested that this finding is a strategy effect unrelated to cerebral dominance and that subjects presented with bilateral stimuli decide to either shadow the right or left channel. Wilson, using unilateral presentation of stimuli to the visual hemifields, found no cerebral asymmetry effects in deaf subjects for the processing of words, letters, or signs. These findings tend to substantiate the view that left-hemisphere superiority for language in hearing subjects results from auditory input to the left auditory association cortex of the brain. Wilson also found that signed stimuli are easier to identify than printed stimuli when the exposure time is brief (20 msec). She attributed this result to the slower decay of spatial information, when compared to the decay of figural information. The possibility that deaf subjects rely on visual codes is also supported by studies of short-term memory. Research has shown that deaf subjects make more formational errors, while hearing subjects make semantic errors (Bellugi, Klima, & Siple, 1975; Wallace, 1972). The study by Wallace (1972) does, however, suggest that the deaf make use of other codes. Wallace found that orally trained subjects showed some evidence of using an articulatory code, while manually taught subjects used a code based partly on fingerspelling. He also noted that the deaf performed better than the hearing on a facial recognition task, again stressing the importance of the visual channel. The use of different encoding strategies has been explored by Boshoven, McNeil, and Harvey (1982). They related these differences to hemispheric specialization for various functions, and suggested that in pro95 Issues in Cognition and Language Development cessing drawings, deaf subjects may use nonverbal referents while hearing subjects use verbal referents. Overall, they suggested that the deaf subjects may have adopted holistic/gestalt processing strategies, whereas hearing subjects may use more analytical strategies. Experimental Studies The authors of this paper have been involved in a number of studies of various aspects of language and cognition (Grove, O'Sullivan, & Rodda, 1979; Rodda & Grove, 1982). These studies are summarized in the following section. Studies of Information Transmission Response latency. The time taken to respond to a stimulus (including transmission time) is a useful way of measuring overall differences in cognitive-processing strategy. In one study by Rodda and Grove (1982), the overall average latency of response (t) to signed and orally communicated sentences was calculated. The regression functions for the two groups of subjects (when r is the coefficient of correlation) were clearly different. Total: TS = 0.871 - O.0044t Oral: TS = 1.04 - 0.023t r = -0.31 n.s. (A) r = -0.61 n.s. (B) With so few degrees of freedom, two-tailed t-tests fail to reach significance, but the trend seems to be fairly clearly established. 1. Total communicators show total scores (TS) that are virtually independent of latency. Also, a very slow responder achieves about the same total score as a fast responder. 2. Oral communicators have total scores that indicate a moderately strong negative relationship between the two variables. Rate of information transfer. The differential relationship just described led to the development of an estimated rate at which information is transmitted during testing (Rodda & Grove, 1982). An arbitrary metric was employed to assess different coding systems (reading, total, oral, and manual). Table 1 shows the mean information transfer rate (ITR) as a function of two age groups (9-13 years and 14-20 years) and method of communication. The overall superiority of reading and the relative weakness of the oral method are emphasized when the transmission rate is taken into account, but the mean ITR rates for total and marlUal methods of communication were almost identical. Laterality Studies In a study by Muendel-Atherstone and Rodda (1983), signed and unsigned stimuli were visually presented to 20 hearing and 20 prelingually deaf 96 Cognitive Processing and Language in Deaf Students: A Decade of Research Table 1 Information Transfer Rate (ITR)a As a Function of Age and Method of Communication Subjects Subjects 9-13 Years Old 14-20 Years Old Communication Group Group Method Size ITR Size ITR Reading 9 2.10 12 2.61 Total 14 1.77 11 2.45 Oral 8 0.95 9 1.72 Manual 8 1.74 13 2.27 aIIR = messages correctly received per minute. All Subjects ITR 2.39 2.07 1.36 2.07 adults. Materials were presented unilaterally in a randomized sequence to both right and left visual hemifields through a two-field tachistoscope. Hearing and deaf subjects differed significantly in the number of correctly identified stimuli, with hearing subjects scoring higher on all six types of materials presented. Four factors were found in the hearing subjects' responses and three factors in the deaf subjects' responses. The factors for hearing subjects were signed presentations, unsigned materials, right hemispheric presentation of road signs, and right hemispheric presentation of letters. In deaf subjects, the factors were signed presentations, road signs, and letters; these factors showed no laterality effects. Because no difference was found between the materials presented to the left and right visual hemifields, the data substantiated the hypotheses that (a) the deaf sign subjects would show an overall reduced laterality effect, and (b) hearing signing subjects would show bilateral effects. Interestingly, and predictably, more road signs were perceived in the left hemisphere in both groups, and both groups tended to more correctly identify materials presented to the left hemisphere. Discussion and Conclusions While previous research into cerebral lateralization of language with hearing-impaired populations has provided some conflicting results and has been open to criticism, it does indicate that the field has promising potential for increasing our understanding of cognitive processing in both hearing and deaf individuals. If deaf individuals acquire a different cerebral organization for language as compared to hearing populations, then such differences could have a considerable impact on the intervention methods used with young children. Even if language is not lateralized differently in deaf children, adolescents , and/or adults, a number of important questions remain to be answered . For example, Does the acoustic code have unique properties or can 97 Issues in Cognition and Language Development the signs of a visually based language (such as American Sign Language) fulfill the same tasks? If such signs can be utilized equally well in the acquisition of language structures, will this acquisition occur in the same way as it does with an acoustic code? How is a language such as ASL processed by both deaf and hearing populations? Are signs mediated equally well by both hemispheres? If so, this mediation could have significance for intervention not only with deaf children but with hearing aphasics who could learn sign language as a means of communication. However, it may be that educational experiences result in patterns of atypicallateralization in deaf subjects. Since atypicallateralization has been associated with cognitive and perceptual deficits in hearing populations (Levy & Reid, 1978), it is also possible that the language problem associated with early prelingual deafness may be a consequence of educational deficits rather than neurological differences. References Bellugi, U., Klima, E. S., & Siple, P. (1975). Remembering in signs. International Journal of Cognitive Psychology, 3, 93-125. Bogen, J. E. (1969). The other side of the brain: An appositional mind. Bulletin of the Los Angeles Neurological Society, 34, 135-162. Boshoven, M. M., McNeil, M. R, & Harvey, L. O. (1982). Hemispheric specialization for the processing of linguistic and non-linguistic stimuli in congenitally deaf and hearing adults. Audiology, 21, 509-530. Grove, c., O'Sullivan, F. D., & Rodda, M. (1979). Communication and language in severely deaf adolescents. British Journal of Psychology, 70, 531-540. Kelly, R R, & Tomlinson-Keasey, C. (1978, June). A comparison of deaf and hearing children's hemispheric lateralization for processing visually presented words and pictures. Paper presented at the 1978 meeting of the American Educational Research Associaton, Toronto, Canada. Kimura, D. (1976). The neural basis of language and gesture. In H. AvakianWhitaker & H. A. Whitaker (Eds.), Studies in neurolinguistics (Vol. 2, pp. 145-156). New York: Academic Press. Kimura, D., Battison, R, & Lubert, B. (1976). Impairment of nonlinguistic hand movements in a deaf aphasic. Brain and Language, 3, 566-571. Levy, J., & Reid, M. (1978). Variations in cerebral organization as a function of handness, hand posture, writing and sex. Journal of Experimental Psychology, 10, 119-144. McKeever, W. F., Hoemann, H. W., Florian, V. A., & Van Deuenter, A. D. (1976). Evidence of minimal cerebral asymmetries for processing of English words and American Sign Language in the congenitally deaf. Neuropsychologia, 14,413-423. Muendel-Atherstone, B., & Rodda, M. (1983). Differences in hemispheric processing of linguistic material presented visually to deaf and hearing adults. Unpublished manuscript , University of Alberta, Department of Educational Psychology. Nebes, R D. (1971). Superiority of the minor hemisphere in a commissurotomized man for perception of part-whole relations. Cortex, 7, 333-347. Nebes, R D. (1972). Dominance of the minor hemisphere in a commissurotomized man in a test of figural unifications. Brain, 95, 633-638. , Nebes, R D. (1973). Perception of dot patterns by the disconnected right and left hemisphere in a commissurotomized man. Neuropsychologia, 11, 285-296. Nebes, R D. (1974). Hemispheric specialization in a commissurotomized man. Psychological Bulletin, 81, 1-14. 98 Cognitive Processing and Language in Deal Students: A Decade 01 Research Phippard, D. (1977). Hemifield differences in visual perception in deaf and hearing subjects. Neuropsychologia, 15, 555-561. Rodda, M., & Grove, C. (1982). A pilot study of language structures in the receptive language of deaf subjects. Journal Association of Canadian Educators of the Hearing Impaired, 8, 168-181. Searleman, A. (1977). A review of right hemispheric linguistic capabilities. Psychological Bulletin, 84, 503-528. Sperry, R. W. (1973). Lateralization of function in the surgically separated hemispheres . In F. J. McGuigan & R. Schoonover (Eds.), The psychophysiology of thinking. New York: Academic Press. Wallace, G. (1972). Short-term memory and coding strategies of the deaf. Unpublished doctoral dissertation, McGill University, Montreal. Wilson, B. (1977). Lateralization of sign language. Unpublished doctoral dissertation, University of London. 99 ...