Priming summation in the cerebral hemispheres: evidence from semantically convergent and semantically divergent primes.

The ability to activate and to maintain a large and relatively undifferentiated semantic field has been thought to be an important component of lexical semantic processing by the right hemisphere (RH). An implication of this unique propensity of the RH was examined in the present study that included two divided visual field priming experiments with SOAs of 800 and 2500 ms. The experiments investigated the ability of the RH and the left hemisphere (LH) to summate activation from multiple primes followed by a laterally presented ambiguous target word. The priming words either converged onto the same semantic representation (i.e. all three words related to either the dominant or to the subordinate meaning of the target) or diverged onto distinct semantic representations (i.e. two words related to the dominant and one to the subordinate meaning of the target, or vice versa). Results indicated that for either an 800 or 2500 ms stimulus onset asynchrony (SOA) the LH benefited most from three semantically convergent primes that converged onto the dominant meaning of the ambiguous target word. There was no facilitation when three subordinate primes preceded the target. When the primes diverged onto different meanings, there was significant facilitation for the 800 ms SOA only. In contrast, with an 800 ms SOA, the RH benefited only from semantically divergent primes, that diverged onto alternate meanings of the ambiguous target word. With a 2500 ms SOA, the RH benefited from all combinations of primes. The discussion focuses on the implications for language processing of the differences between the two hemispheres in the scope and temporal pattern of the multiple prime effect.