Elliott R, Dolan R J
Wellcome Department of Cognitive Neurology, Institute of Neurology, London WC1N 3BG, United Kingdom.
J Neurosci. 1998 Jun 15;18(12):4697-704. doi: 10.1523/JNEUROSCI.18-12-04697.1998.
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.
让受试者预先接触视觉刺激足以建立随后的偏好，即使之前的接触是阈下的，以至于明确的识别是随机的。先前接触对偏好判断的这种影响，即所谓的“单纯接触效应”，是一种无意识记忆的形式。目前的功能神经影像学研究考察了这种效应的机制。九名志愿者受试者在进行功能成像研究时，基于偏好或记忆对抽象刺激做出强制选择判断。每种判断类型都在两种条件下进行：在一种条件下，一种或另一种刺激先前已被阈下呈现，而在第二种条件下，两种刺激都是新的。记忆判断与左额极皮层和顶叶区域的激活有关，而偏好判断与内侧前额叶皮层和枕叶区域的激活有关。客观熟悉度（内隐记忆）对偏好的调节与右侧额叶激活有关。无论需要何种判断类型，海马回对客观刺激新颖性均有显著激活。因此，我们的数据证明了一个独立于回忆体验的记忆系统的激活。该系统内可分离的激活表明额极参与明确的检索尝试，右侧前额叶皮层参与偏好判断中表达的内隐记忆。此外，结果表明海马对刺激新颖性的反应可以独立于熟悉度的意识可报告性。
