Transfer of Dominance in Speed of Verbal Response to Visually Presented Stimuli from Right to Left Hemisphere

Abstract

Transfer of cerebral dominance from the right to the left hemisphere was demonstrated for a response-time task of verbal naming of novel, visually presented symbols. Four sets of stimuli were used: (1) familiar numbers in the typical Arabic script; (2) Gothic-like numbers; (3) binary numbers presented in a form using dots rather than digits; and (4) symbols taken from the Digit Symbol subtest of the WAIS. Stimuli from each of these four sets were quickly flashed unpredictably to either the left or right visual half-field. Response latency was measured until the subject repeated vocally the name of the number represented by the symbol. The results show that the new symbols, e.g., binary numbers and symbols, were recognized faster by the right hemisphere at the beginning of the test session and by the left hemisphere toward the end. By contrast, numbers in familiar script showed no such hemisphere shift; dominance was constant and remained in the left hemisphere throughout. It was hypothesized that the recognition ability of the right hemisphere produced the initial superiority of the left field whereas the encoding function of the left hemisphere produced the switch to the right field. The suggestion is advanced that the new symbols used in the present study are not much different a priori than symbols normally used for language, i.e., letters, words, and therefore the abilities of the right hemisphere may be critical in acquisition of reading before and concurrently with acquisition of general language skills by the left (language) hemisphere.