Rajimehr Reza, Montaser-Kouhsari Leila, Afraz Seyed-Reza
Cognitive Neuroscience Department, School of Intelligent Systems (SIS), Institute for Studies in Theoretical Physics and Mathematics (IPM), Niavaran, PO Box 19395-5746, Tehran, Iran.
Perception. 2003;32(10):1199-210. doi: 10.1068/p5076.
Visual adaptation has been successfully used as a psychophysical tool for studying the functional organisation of visual awareness. It has been shown that orientation-selective adaptation to a grating pattern occurs in crowded conditions. In such conditions, simultaneous presentation of flanking distractors pushes the target stimulus out of conscious perception and severely impairs orientation discrimination in the periphery of the visual field. In the present study, orientation-selective adaptation to illusory lines induced by two line gratings abutting each other with a phase shift was examined in crowded and non-crowded conditions. To rule out the effects of lower level adaptations we used an animation paradigm in which the orientations of the two line gratings were altered repeatedly during adaptation phase without any change in the orientation of the resulting illusory line. Although performance of subjects in reporting the orientation of crowded illusory lines was at chance level, orientation-selective adaptation was preserved for crowded as well as non-crowded adapting targets. Two control experiments demonstrated that adaptation to endpoints of real lines at the location of abutting grating lines had minimal effect on the adaptation to illusory lines; and changes in the configuration of endpoints could not be responsible for better performance when adapting and test stimuli were different. We conclude that a crowding effect occurs after illusory lines have been processed in the visual stream. Since illusory lines seem to be represented at relatively early stages of visual processing (e.g. area V2), adaptation to crowded illusory stimuli suggests that neuronal activation in those early stages is not necessarily correlated with conscious perception.
视觉适应已成功用作研究视觉意识功能组织的心理物理学工具。研究表明，在拥挤条件下会出现对光栅图案的方向选择性适应。在这种条件下，同时呈现侧翼干扰物会使目标刺激脱离意识感知，并严重损害视野周边的方向辨别能力。在本研究中，我们在拥挤和非拥挤条件下，研究了对由两个相互邻接且有相位偏移的线条光栅诱导的虚幻线条的方向选择性适应。为了排除较低层次适应的影响，我们使用了一种动画范式，即在适应阶段，两个线条光栅的方向反复改变，而产生的虚幻线条的方向没有任何变化。尽管受试者报告拥挤虚幻线条方向的表现处于随机水平，但对拥挤和非拥挤适应目标都保留了方向选择性适应。两项对照实验表明，对邻接光栅线条位置处真实线条端点的适应对虚幻线条的适应影响最小；当适应刺激和测试刺激不同时，端点配置的变化不能解释更好的表现。我们得出结论，在视觉流中处理虚幻线条后会出现拥挤效应。由于虚幻线条似乎在视觉处理的相对早期阶段（例如V2区）就有表征，对拥挤虚幻刺激的适应表明，这些早期阶段的神经元激活不一定与意识感知相关。
