An Examination of Automatic Versus Strategic Semantic Priming Effects in Broca's Aphasia.

Abstract

The ability to recognize words is frequently investigated using a lexical decision (LD) priming task in which subjects make rapid yes/no judgements as to whether visually presented letter strings (targets) are words or not. A well established finding is that words are recognized faster when preceded by related words. This "semantic priming effect" is believed to represent both automatic and conscious, strategic driven processes. One factor that influences the degree to which subjects recognize words automatically or consciously, is the time interval between the presentation of the prime and the presentation of the target. This is referred to as the stimulus onset asynchrony (SOA). Automatic processing tends to occur with short SOAs whereas strategic processing is generally observed with longer SOAs. Experiment I examined the claims of the Neely and Keefe hybrid three process theory of priming (1989). An attempt was made to dissociate the three priming mechanisms described within this theory (automatic spreading activation, expectancy, and semantic matching) by examining priming across multiple SOAs in a visual pairwise LD task. The results provided clear support for the operation of automatic spreading activation in the short SOA conditions, but less convincing support for strategic processing in the longer SOA conditions. Experiment 2 examined the nature of automatic versus strategic priming effects in Broca's aphasia. Broca's aphasics, age-matched controls, and young controls participated in a visual pairwise LD task in a 250 SOA condition. A neutral priming condition was included to measure the contribution of facilitatory and inhibitory influences to the overall priming effect. Unlike the young normal controls, the age-matched controls and the Broca's aphasics displayed inhibitory priming effects, indicating the use of strategic processing in this short SOA condition. These results suggest that automatic processing is impaired in Broca's aphasia, and perhaps declines with normal aging as well. Furthermore, they support the hypothesis that subjects will resort to the use of conscious strategies in the LD task, even in short SOA conditions, if unable to process the stimuli automatically.