Extending local-global processing to the semantic domain: the role of stimulus context

Abstract

The current set of experiments tested the view that there are mechanisms common to visual and semantic processing, and they relate to general properties of the right and left hemispheres. Two properties of local-global visual processing were tested with semantic stimuli to determine if the properties apply to both the visual and semantic domains. In Part 1 the property explored was that the visual local-global distinction between the left and right hemispheres is relative rather than absolute, based on the properties of the stimulus set (Robertson & Ivry, 2000). A divided visual field technique was used with sentence stems centrally presented and sentence endings laterally presented for initial processing in the contralateral hemisphere, allowing for examination of lateralized timing differences in processing. Unlike medium spatial frequency local-global visual stimuli, metaphors of medium familiarity did not show different patterns of lateralization depending on whether they were processed in the context of high versus low familiarity metaphors. Results indicated, however, that it is necessary to have a broad range of familiarity in a stimulus set in order to obtain a right hemisphere advantage for low familiar metaphors. In Part 2, the property explored was that priming occurs based on the level of processing, local or global (the level repetition effect; Robertson, 1996). Metaphorical sentences and priming word pairs were presented centrally for ease of understanding or relatedness judgments, respectively. It was hypothesized that reaction time priming would occur based on the familiarity or association level of the preceding trial, as with visual stimuli. A strong effect of preceding trial was obtained, but it was based on following a high association trial, rather than following a trial at the same level of association, as is the ease for visual stimuli. For the sentential stimuli, a delayed level repetition effect was obtained, showing faster processing of metaphors low in familiarity following several sequential low familiar trials. Generally speaking, these experiments demonstrate that the processing of semantic stimuli is affected by the surrounding stimulus context; specifically levels of familiarity in the surrounding stimuli, in both the overall stimulus set, and the immediately preceding trials.