Academic journal article Canadian Journal of Experimental Psychology

Functional Mapping of Human Memory Using PET (Positron Emission Tomography): Comparisons of Conceptual and Perceptual Tasks

Academic journal article Canadian Journal of Experimental Psychology

Functional Mapping of Human Memory Using PET (Positron Emission Tomography): Comparisons of Conceptual and Perceptual Tasks

Article excerpt

Abstract An experiment is reported in which regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) as participants performed conceptual and perceptual memory tasks. Blood flow during two conceptual tests of semantic cued recall and semantic association was compared to a control condition in which participants made semantic associations to nonstudied words. Analogously, rCBF during two perceptual tasks of word fragment cued recall and word fragment completion was compared to a word fragment nonstudied control condition. A direct comparison of conceptual and perceptual tasks showed that conceptual tasks activated medial and lateral left hemisphere in frontal and temporal regions as well as the lateral aspect of bilateral inferior parietal lobule. Perceptual tasks, in contrast, produced relatively greater activation in right frontal and temporal cortex as well as bilateral activation in more posterior regions. Comparisons of the memory tasks with their control conditions revealed memory - specific deactivations in left medial and superior temporal cortex as well as left frontal cortex for both conceptual tasks. In contrast, memory - specific deactivations for both perceptual fragment completion tests were localized in posterior regions including occipital cortex. Results from this and other functional imaging experiments provide evidence that conceptual and perceptual memory processes are subserved, at least in part, by different neurological structures in the human brain.

The search for an explanation as to why memory performance can be dissociated, or uncorrelated, across different retention tasks is a matter of fundamental importance to memory researchers. Various approaches have been taken by theorists seeking to account for the patterns of dissociations obtained among memory measures (e.g., Schacter, 1992; Squire, 1987; Tulving & Schacter, 1990), both for memory - impaired subject groups (Moscovitch, Vriezen, & Goshen - Gottstein, 1993; Schacter, Chiu, & Ochsner, 1993; Squire, Knowlton, & Musen, 1993) and normal volunteers (Roediger & McDermott, 1993). One such account is based on distinctions among the types of processing required for various encoding and retrieval tasks. According to this transfer appropriate processing principle, memory will be enhanced to the degree that processes performed during encoding are recapitulated at time of retrieval (e.g., Jacoby, 1983; Kolers & Roediger, 1984; Morris, Bransford, & Franks, 1977; Roediger & Blaxton, 1987b). On the other hand, mismatches in the type of processing required at study and test produce poor performance relative to situations in which processing demands are held constant.

It has been suggested that dissociations will commonly be obtained between tasks requiring conceptual processing of meaning and tasks that are more perceptually driven, requiring processing of the physical features of stimuli apart from their semantic content (Jacoby, 1983; Roediger, 1990; Roediger & McDermott, 1993). During the past decade, many experiments testing normal subjects have been reported in which performance on conceptual and perceptual tasks has been dissociated. These include demonstrations from experiments investigating such diverse topics as the generation effect (e.g., Blaxton, 1989; Jacoby, 1983), levels of processing (e.g., Hamann, 1990; Jacoby & Dallas, 1981), modality effects (e.g., Kirsner, Dunn, & Standen, 1989; Rajaram & Roediger, 1993), effects of imagery during encoding (e.g., Blaxton, 1989; Roediger & Blaxton, 1987a), the picture superiority effect (e.g., Weldon & Roediger, 1987), priming in person perception (Smith & Branscombe, 1988), and cross - language priming in bilingual subjects (e.g., Durgunoglu & Roediger, 1987; Gerard & Scarborough, 1989).

The majority of experimental demonstrations supporting the process theory have come from behavioral experiments testing normal healthy participants. …

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