Recent advances in experimental neuropsychology have complemented the traditional aphasiological approach to neurolinguistics by data from commissurotomy patients and normal subjects. The three approaches often use different paradigms and reach opposite conclusions. In this proposal I outline a series of paradigms and experiments that will be applied concurrently to all three populations: left brain-damaged aphasics, split brain patients, and normal subjects. The experiments aim to clarify the nature of left hemisphere specialization for language, the role of the right-hemisphere in language, the relation of other cognitive functions to the linguistic competence in each hemisphere, and the linguistic significance of interhemispheric interaction. The paradigms include a contact lens system for continuous lateralization of visual information with free ocular scanning, an eye-tracker driven universal half-field occluder with no attachments to the eye, hemified tachistoscopy, dichotic listening and dual task interference. The experiments focus on possible lexical representation and transformation in the two cerebral hemispheres, at both the conscious and preattentive stages of information processing. In the disconnected right hemisphere I study especially syntatic factors in auditory language comprehension, reading without phonological encoding, and noncallosal interhemispheric semantic transfer. In aphasics I study the conditions and nature of right hemisphere support of language recovery at the lexical level following left sided damage, and the role of phonological representation deficit in aphasia diagnostics. In normal subjects I study models of laterality effects in hemifield tachistoscopy and dichotic listening experiments and their applications to individual differences; the role of the normal right hemisphere in reading; and experimental conditions that create functional disconnection or, on the contrary, control interhemispheric integration. The ultimate goal is to formulate general principles of brain organization that interface anatomical-physiological constraints with a processing account of higher functions.
