Murray Micah M, Wylie Glenn R, Higgins Beth A, Javitt Daniel C, Schroeder Charles E, Foxe John J
The Cognitive Neurophysiology Laboratory, Program in Cognitive Neuroscience and Schizophrenia, Nathan S. Kline Institute for Psychiatric Research, Orangeburg, New York 10962, USA.
J Neurosci. 2002 Jun 15;22(12):5055-73. doi: 10.1523/JNEUROSCI.22-12-05055.2002.
Because environmental information is often suboptimal, visual perception must frequently rely on the brain's reconstruction of contours absent from retinal images. Illusory contour (IC) stimuli have been used to investigate these "filling-in" processes. Intracranial recordings and neuroimaging studies show IC sensitivity in lower-tier area V2, and to a lesser extent V1. Some interpret these data as evidence for feedforward processing of IC stimuli, beginning at lower-tier visual areas. On the basis of lesion, visual evoked potentials (VEP), and neuroimaging evidence, others contend that IC sensitivity is a later, higher-order process. Whether IC sensitivity seen in lower-tier areas indexes feedforward or feedback processing remains unresolved. In a series of experiments, we addressed the spatiotemporal dynamics of IC processing. Centrally presented IC stimuli resulted in early VEP modulation (88-100 msec) over lateral-occipital (LOC) scalp--the IC effect. The IC effect followed visual response onset by 40 msec. Scalp current density topographic mapping, source analysis, and functional magnetic resonance imaging results all localized the IC effect to bilateral LOC areas. We propose that IC sensitivity described in V2 and V1 may reflect predominantly feedback modulation from higher-tier LOC areas, where IC sensitivity first occurs. Two additional observations further support this proposal. The latency of the IC effect shifted dramatically later (approximately 120 msec) when stimuli were laterally presented, indicating that retinotopic position alters IC processing. Immediately preceding the IC effect, the VEP modulated with inducer eccentricity--the configuration effect. We interpret this to represent contributions from global stimulus parameters to scene analysis. In contrast to the IC effect, the topography of the configuration effect was restricted to central parieto-occipital scalp.
由于环境信息往往并非理想状态，视觉感知常常必须依赖大脑对视网膜图像中缺失轮廓的重建。虚幻轮廓（IC）刺激已被用于研究这些“填补”过程。颅内记录和神经成像研究表明，较低层级的V2区域存在IC敏感性，V1区域的敏感性则稍低。一些人将这些数据解释为IC刺激从较低层级视觉区域开始进行前馈处理的证据。基于损伤、视觉诱发电位（VEP）和神经成像证据，另一些人则认为IC敏感性是一个较晚的高阶过程。较低层级区域中观察到的IC敏感性究竟是前馈还是反馈处理的指标，这一问题仍未解决。在一系列实验中，我们研究了IC处理的时空动态。中央呈现的IC刺激导致枕外侧（LOC）头皮上出现早期VEP调制（88 - 100毫秒）——即IC效应。IC效应在视觉反应开始后40毫秒出现。头皮电流密度地形图、源分析和功能磁共振成像结果均将IC效应定位到双侧LOC区域。我们提出，V2和V1中描述的IC敏感性可能主要反映了来自较高层级LOC区域的反馈调制，而IC敏感性首先出现在该区域。另外两个观察结果进一步支持了这一观点。当刺激从侧面呈现时，IC效应的潜伏期显著延迟（约120毫秒），这表明视网膜位置会改变IC处理。在IC效应出现之前，VEP会随着诱导物偏心度进行调制——即构型效应。我们将此解释为全局刺激参数对场景分析的贡献。与IC效应不同，构型效应的地形图仅限于中央顶枕头皮区域。
