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Abstract:
Previous experiments (Graf & Ryan, 1990) have indicated
that the accuracy with which subjects read words presented in
unusual visual formats (such as backwards orientation) is enhanced
by a prior presentation of the same words. Moreover, priming is
greatest when the visual format of the first and second
presentation of the word match. For example, priming for
backward-oriented words is largest when the previous words are also
presented backwards. However, previous words presented in normal
forward orientation also produce significant, albeit diminished,
priming. Theoretical views of visual format-specific memory suggest
that priming is mediated by at least two separable processes
associated with a) the word meaning and b) visual format-specific
processing. The present study examined this phenomenon using
functional magnetic resonance imaging (fMRI). While undergoing fMRI
scanning, ten subjects read a series of words that were either
presented in forward or backwards orientation. During subsequent
scanning, subjects then re-read the same set of words either in the
same orientation (backward -- backward) or reversed (forward --
backward). Results indicated that visual format-specific priming
involved reductions in both anterior temporal/lateral pre-frontal
regions and posterior occipital/temporal regions. In contrast,
visual non-specific priming involved reductions only in anterior
temporal and lateral pre-frontal regions. The results are
consistent with the view that posterior regions mediate visual
processing of the words; in this case, letter rotation and
left-to-right letter-by-letter reading, while more anterior regions
may be specific to semantic processing of the words. Both anterior
and posterior regions mediate priming depending upon the specific
overlap between the study and test presentations.
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