Semantic priming and retrieval from lexical memory: Roles of inhibitionless spreading activation and limited-capacity attention.

Prior to each visually presented target letter string in a speeded word-nonword classification task, either BIRD, BODY, BUILDING, or xxx appeared as a priming event. When the target was a word, it was (a) a name of a type of bird on most BiRD-prime trials; (b) a name of part of a building on most BODY-prime trials; (c) a name of a part of the body on most BUiLDiNG-prime trials; (d) a name of a type of bird, part of a building, or part of the body equally often on xxx-prime trials. Thus, on BiRD-prime trials the subject expected the word target to be chosen from the same category as the category represented by the word prime itself (Nonshift), whereas on BODY-prime and BuiLDiNG-prime trials the subject's attention was to be shifted because he or she expected the word target to be chosen from a category other than the category represented by the word prime itself (Shift). The word target was an exemplar of either the category the subject expected (Expected) or a category the subject did not expect (Unexpected) and was either semantically related (Related) or semantically unrelated (Unrelated) to the word prime. Thus, there were five different types of word-prime-word-target trials: (a) BiRD-robin (Condition Nonshift-Expected-Related) ; (b) BiRD-arm (Condition Nonshift-Unexpected-Unrelated) ; (c) BODY-door (Condition Shift-Expected-Unrelated) ; (d) BODY-sparrow (Condition Shift-Unexpected-Unrelated); (e) BODYheart (Condition Shift-Unexpected-Related). The stimulus onset asynchrony (SOA) between the prime and the target letter string varied between 250 and 2,000 msec. At the 2,000-msec SOA, reaction times (RTs) on BiRD-robin type trials were faster than RTs on xxx-prime trials (a facilitation effect), whereas RTs on BIRDarm type trials were slower than RTs on xxx-prime trials (an inhibition effect). As SOA decreased, the facilitation effect on BiRD-robin trials remained constant, but the inhibition effect on BiRu-arm trials decreased until, at the 250-msec SOA, there was no inhibition. For the Shift conditions at the 2,000-msec SOA, facilitation was obtained on BODY-door type trials and inhibition was obtained on BODY-sparrow type trials. These two effects decreased in magnitude as the SOA decreased until, at the 250-msec SOA, there was no facilitation or inhibition. On BODY-heart type trials, there was an inhibition effect at the 2,000 msec SOA, which decreased as the SOA decreased until, at the 250-msec SOA, it became a facilitation effect. For the nonword targets, the facilitatory effects of the word primes decreased as SOA decreased. These results were regarded as supporting the theory of Posner and Snyder that postulates two distinct components of attention: a fast automatic inhibitionless spreading-activation process and a slow limited-capacity consciousattention mechanism.