The Journal of Neuroscience, June 15, 1998, 18(12):4697-4704
Neural Response during Preference and Memory Judgments for
Subliminally Presented Stimuli: A Functional Neuroimaging Study
Rebecca
Elliott1 and
Raymond J.
Dolan1, 2
1 Wellcome Department of Cognitive Neurology, Institute
of Neurology, London WC1N 3BG, United Kingdom, and
2 Royal Free Hospital School of Medicine, London, NW3 2PF,
United Kingdom
Preexposing subjects to visual stimuli is sufficient to establish a
subsequent preference, even when previous exposure is subliminal, such
that explicit recognition is at chance. This influence of previous
exposure on preference judgments, known as the "mere exposure
effect," is a form of unconscious memory. The present functional
neuroimaging study examines the mechanism of this effect. Nine
volunteer subjects were studied using functional imaging while making
forced choice judgments about abstract stimuli on the basis of either
preference or memory. Each judgment type was made under two conditions:
under one condition one or the other stimulus had previously been
presented subliminally, whereas under the second condition both stimuli
were novel. Memory judgments were associated with activation of left
frontopolar cortex and parietal areas, whereas preference judgments
were associated with activation of medial prefrontal cortex and regions
of occipital cortex. The modulation of preference by objective
familiarity (implicit memory) was associated with right lateral frontal
activation. Significant activation of hippocampal gyrus was seen in
response to objective stimulus novelty, regardless of judgment type
required. Our data thus demonstrate activations of a memory system
independent of recollective experience. Dissociable activations within
this system implicate a frontopolar involvement in explicit retrieval attempt and right lateral prefrontal cortex involvement in implicit memory expressed in preference judgments. Furthermore, the results suggest that hippocampal response to stimulus novelty can be
independent of conscious reportability of familiarity.
Key words:
episodic retrieval; implicit memory; subliminal
presentation; hippocampal gyrus; prefrontal cortex; positron emission
tomography
Copyright © 1998 Society for Neuroscience 0270-6474/98/18124697-08$05.00/0
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