chapter  11
18 Pages

Cortical Model for Visual Thinking by Profoundly Deaf Persons: Carol A. Lyons

Differences in cognitive, social, and emotional development have been recognized between deaf and hearing persons for a long time. Traditionally, the differences have been based on a developmental lag model (Suppes, 1974; Norden, 1981), however, some researchers (Tomlinson-Keasey & Kelly, 1978; Waldron & Honeywell, 1978, 1980; Ashton & Beasley, 1982) have proposed an acquisitional difference model. The suggestion has been made that congenitally deaf individuals may develop cognitive structures that differ from those of normally hearing people. This difference may be due to the absence of auditory coding which results in a cortical reorganization. Based on this theory, Waldron (1982b) proposed that for congenitally profoundly hearing impaired persons, speech development utilizes a tachemic code available from the tactile senses. Several authors in the field of aural rehabilitation for profoundly hearing impaired children have discussed "residual hearing" (Ling, 1976; Orlando, 1975; Sanders, 1971) and contended that this is not hearing, but rather a sense of feeling (Goldstein & Stark, 1976). Physically and physiologically it is explainable by the fact that acoustic outputs of 128-140 dB are required to stimulate the "residual hearing" sense. The ear saturates beyond the threshold of pain, whereas the hearing organs are not designed to operate at this amplitude level. A well established principle in electrical engineering is that frequency information processing cannot be performed by a device operating in saturation. Risberg (1968) reported that placing the ear piece in the hand or in

the ear produced no difference in word recognition scores for the profoundly deaf. Erber (1974) reported that there was a sudden drop (from 80% to 15%) in Spondee word recognition when the mean hearing loss changed from less than 85 dB (for the severely deaf) to greater than 95 dB (for the profoundly deaf). He also reported that this was supported by at least three other researchers. Erber (1972) also examined the confusion matrices of normally hearing, severely hearing impaired, and profoundly hearing impaired children. The confusion matrices were constructed for auditory, visual, and auditory-visual recognition of eight plosive and nasal consonants. He found that with auditory-visual stimulation, the severely hearing impaired student's confusion matrix was diagonalized (over visual stimulation). Conversely, the profoundly deaf subjects demonstrated very slight improvement in the diagonalization of their confusion matrices between visual only and auditory-visual presentation of sounds. Luria (1973) contends that the brain consists of complex functional systems which are interrelated throughout the cortex. Mykelbust (1964), Haber (1974), and others have hypothesized that an early sensory deprivation to a functional system could alter the integration of other functions. Based on this theory, several studies have been conducted of cortical organization of the human brain.