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Abstract:
Theories of memory function suggest that memory traces left
by particular stimuli reside in the brain areas first involved in
processing the stimuli. This leads to the prediction that
laterally-presented visual stimuli leave different memory traces in
the hemispheres contralateral and ipsilateral to the side of
initial stimulus presentation. In previous work (Fabiani et al., in
press; Gratton et al., 1997, 1998) we showed evidence supporting
this prediction. Two organizational principles are compatible with
these data: a local principle (memory traces are associated with
specific locations), and a hemispheric principle (memory traces are
associated with each hemisphere). In a series of experiments,
laterally-presented items to be memorized were followed, on some
trials, by masks presented at different locations of the visual
field. The masks interfered with memory performance only if
presented in the same hemifield as the stimulus to be memorized.
Whereas there was a further interference when the mask was
presented at the same exact location as the to-be-memorized
stimuli, all other locations within the same hemifield led to a
similar performance decrement. We also used measures of brain
activity (event-related brain potentials, ERPs, and the
event-related optical signal, EROS) to evaluate whether the masks
interfered with the patterns of lateralized brain activity observed
at test as a function of encoding side. Taken together the findings
support both the local and the hemispheric principles of visual
memory organization.
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