DIFFERENTIAL
INTERHEMISPHERIC
TRANSFER
FOR
ABSTRACT AND
SPECIFIC
VISUAL-FORM
INFORMATION
Christopher D. Nicholas & Chad J. Marsolek
University of Arizona
(Presented at the 3rd Annual Meeting of the Cognitive Neuroscience Society, San Fransisco, CA, April 1996)
Abstract
When subjects compare two visually presented letters, interhemispheric transfer
of visual information must take place when the letters are displayed briefly in
different visual fields (i.e., across-hemispheres [AH]), but not when they are
displayed briefly in the same visual field (i.e., within-hemisphere [WH]). In an
abstract comparison task, subjects decide whether pairs correspond to the same
letter (e.g., s/S, a/A) or not (e.g., s/A, a/S) and perform more accurately in AH
than in WH trials. In a specific comparison task, subjects decide whether pairs
are physically the same (e.g., s/s, a/a) or not (e.g., s/S, a/A) and perform more
accurately in WH than in AH trials. One interpretation of this pattern of
results from other laboratories is that AH advantages are found for complex tasks
because the benefits of distributing component processes (e.g., visual analysis
and name comparison) across hemispheres outweigh the costs of transfer, whereas
WH advantages are found for simple tasks because the costs of transfer outweigh
any benefits of distributing a simple process (e.g., visual comparison).
However, we suggest that abstract visual-form (AVF) and specific visual-form
(SVF) subsystems underlie the two tasks, respectively, and are differentially
affected by interhemispheric transfer. Tasks requiring an AVF subsystem should
produce AH advantages, because this subsystem processes relatively invariant
features of letters which may transfer effectively. If so, the AH advantage in
the abstract task should be greater for similar- (e.g., s/S) than for
dissimilar-case letters (e.g., a/A), because greater amounts of relatively
invariant information per letter are found in the former than in the latter.
Tasks requiring an SVF subsystem should produce WH advantages, because this
subsystem processes fine-grained distinctive information which may not transfer
effectively. If so, the WH advantage in the specific task should be greater for
similar- than for dissimilar-case letters, because finer-grained distinctive
information is needed to distinguish the former than the latter. Recent results
support these predictions.
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