Cornelissen Frans W, Wade Alex R, Vladusich Tony, Dougherty Robert F, Wandell Brian A
NeuroImaging Centre, School of Behavioural and Cognitive Neurosciences, University Medical Centre Groningen, University of Groningen, Groningen 9700 RB, The Netherlands.
J Neurosci. 2006 Apr 5;26(14):3634-41. doi: 10.1523/JNEUROSCI.4382-05.2006.
The brightness and color of a surface depends on its contrast with nearby surfaces. For example, a gray surface can appear very light when surrounded by a black surface or dark when surrounded by a white surface. Some theories suggest that perceived surface brightness and color is represented explicitly by neural signals in cortical visual field maps; these neural signals are not initiated by the stimulus itself but rather by the contrast signals at the borders. Here, we use functional magnetic resonance imaging (fMRI) to search for such neural "filling-in" signals. Although we find the usual strong relationship between local contrast and fMRI response, when perceived brightness or color changes are induced by modulating a surrounding field, rather than the surface itself, we find there is no corresponding local modulation in primary visual cortex or other nearby retinotopic maps. Moreover, when we model the obtained fMRI responses, we find strong evidence for contributions of both local and long-range edge responses. We argue that such extended edge responses may be caused by neurons previously identified in neurophysiological studies as being brightness responsive, a characterization that may therefore need to be revised. We conclude that the visual field maps of human V1 and V2 do not contain filled-in, topographical representations of surface brightness and color.
一个表面的亮度和颜色取决于它与附近表面的对比度。例如,一个灰色表面在被黑色表面包围时可能显得很亮,而在被白色表面包围时则可能显得很暗。一些理论认为,感知到的表面亮度和颜色由皮层视野图中的神经信号明确表示;这些神经信号不是由刺激本身引发的,而是由边界处的对比度信号引发的。在这里,我们使用功能磁共振成像(fMRI)来寻找这种神经“填充”信号。虽然我们发现局部对比度与fMRI反应之间通常存在很强的关系,但当通过调制周围区域而不是表面本身来诱导感知到的亮度或颜色变化时,我们发现在初级视觉皮层或其他附近的视网膜拓扑图中没有相应的局部调制。此外,当我们对获得的fMRI反应进行建模时,我们发现有强有力的证据表明局部和远距离边缘反应都有贡献。我们认为,这种扩展的边缘反应可能是由神经生理学研究中先前确定为对亮度有反应的神经元引起的,因此这种特征可能需要修正。我们得出结论,人类V1和V2的视野图不包含表面亮度和颜色的填充式、地形图式表示。