DIVERGENT THINKING STYLES OF THE HEMISPHERES - HOW SYLLOGISMS ARE SOLVED DURING TRANSITORY HEMISPHERE SUPPRESSION

Psychiatric patients solved syllogisms while recovering from transitor y ictal suppression of one hemisphere by electroconvulsive therapy (EC T). The premises were familiar or unfamiliar, true or false. While the right hemisphere was suppressed, syllogisms were usually solved by th eoretical, deductive reasoning even when the factual answer was known a priori, the premises were obviously false and the conclusions were a bsurd. While their left hemisphere was suppressed, the same subjects a pplied their prior knowledge; if the syllogism content was unfamiliar or false, they refused to answer. We postulate a left-hemisphere mecha nism capable of decontextualized mental operations and a right-hemisph ere mechanism, the operation of which is context-bound and incapable o f abstraction. We show that each hemisphere tends to overextend its pe rspective on the problem and that in the intact brain they both contri bute to an extent that depends on the characteristics of the problem a t hand. (C) 1996 Academic Press, Inc.