Thiele A, Dobkins K R, Albright T D
The Salk Institute for Biological Studies, San Diego, California 92186, USA.
J Neurosci. 1999 Aug 1;19(15):6571-87. doi: 10.1523/JNEUROSCI.19-15-06571.1999.
The chromatic properties of an image yield strong cues for object boundaries and thus hold the potential to facilitate the detection of object motion. The extent to which cortical motion detectors exploit chromatic information, however, remains a matter of debate. To address this further, we quantified the strength of chromatic input to directionally selective neurons in the middle temporal area (MT) of macaque cerebral cortex using an equivalent luminance contrast (EqLC) paradigm. This paradigm, in which two sinusoidal gratings, one heterochromatic and the other achromatic, are superimposed and moved in opposite directions, allows the sensitivity of motion detectors to heterochromatic stimuli to be quantified and expressed relative to the benchmark of sensitivity for a luminance-defined stimulus. The results of these experiments demonstrate that the chromatic contrast in a moving red-green heterochromatic grating strongly influences directional responses in MT when the luminance contrast in that same grating is relatively low; for such stimuli, EqLC is at least 5%. When luminance contrast is added to the heterochromatic grating, however, EqLC wanes sharply and becomes negative (-4%) when luminance contrast is sufficiently high (>17-23%). Thus, the chromatic properties of an object appear to confer little or no benefit to motion processing by MT neurons when sufficient luminance contrast concurrently exists. These data support a simple model in which chromatic motion processing in MT is almost exclusively determined by magnocellular input. Additionally, a comparison of neuronal and psychophysical data suggests that MT may not be the sole contributor to the perceptual experience elicited by motion of heterochromatic patterns, or that only a subset of MT neurons serve this function.
图像的色彩特性为物体边界提供了强烈线索，因此具有促进物体运动检测的潜力。然而，皮质运动探测器在多大程度上利用色彩信息仍是一个有争议的问题。为了进一步探讨这一点，我们使用等效亮度对比度（EqLC）范式，量化了猕猴大脑皮质颞中区（MT）中方向选择性神经元的色彩输入强度。在这个范式中，将一个异色正弦光栅和一个消色差正弦光栅叠加并沿相反方向移动，这样就可以量化运动探测器对异色刺激的敏感度，并相对于亮度定义刺激的敏感度基准来表示。这些实验结果表明，当移动的红-绿异色光栅中的亮度对比度相对较低时，其色彩对比度会强烈影响MT中的方向反应；对于此类刺激，EqLC至少为5%。然而，当在异色光栅中加入亮度对比度时，EqLC会急剧下降，当亮度对比度足够高（>17%-23%）时，EqLC会变为负值（-4%）。因此，当同时存在足够的亮度对比度时，物体的色彩特性似乎对MT神经元的运动处理几乎没有益处。这些数据支持了一个简单的模型，即MT中的色彩运动处理几乎完全由大细胞输入决定。此外，对神经元数据和心理物理学数据的比较表明，MT可能不是异色模式运动引发的感知体验的唯一贡献者，或者只有一部分MT神经元发挥这一功能。
