Qian N, Andersen R A
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139, USA.
Exp Brain Res. 1995;103(1):41-50. doi: 10.1007/BF00241963.
It is well known that a stimulus composed of two independent sets of random dots moving in opposite directions produces a percept of two overlapping transparent surfaces moving across each other, while a counterphase grating composed of two identical sine wave gratings drifting in opposite directions does not. We recorded from the directionally selective V1 cells of behaving macaque monkeys using these two types of stimuli in order to investigate the physiological basis of transparent motion perception. Previous single-unit recording experiments from our laboratory indicated that many V1 cells respond well to transparent random dot patterns, while MT cells' responses to the same patterns are strongly suppressed in comparison with their preferred direction responses. This observation alone would seem to suggest that V1 activity could better explain transparent motion perception than MT activity. However, one could argue to the contrary based on the psychophysical observation that there is a motion threshold elevation under the transparency condition. We decided to determine the correlation between V1 activity and the transparent motion perception directly by recording from V1 cells using both transparent random dot patterns and nontransparent counterphase gratings. It is found that V1 cells on the average could not reliably tell the two types of patterns apart. Our results further the idea that additional processing beyond V1 is involved in transparent motion analysis.
众所周知，由两组独立的、朝相反方向移动的随机点组成的刺激会产生两个相互重叠的透明表面相互穿过的感知，而由两个朝相反方向漂移的相同正弦波光栅组成的反相光栅则不会。我们使用这两种类型的刺激对行为猕猴的方向选择性V1细胞进行记录，以研究透明运动感知的生理基础。我们实验室之前的单单元记录实验表明，许多V1细胞对透明随机点图案反应良好，而MT细胞对相同图案的反应与其偏好方向反应相比受到强烈抑制。仅这一观察结果似乎表明，与MT活动相比，V1活动能更好地解释透明运动感知。然而，基于心理物理学观察，即在透明条件下存在运动阈值升高的情况，有人可能会提出相反的观点。我们决定通过使用透明随机点图案和非透明反相光栅记录V1细胞，直接确定V1活动与透明运动感知之间的相关性。结果发现，V1细胞平均无法可靠地区分这两种类型的图案。我们的结果进一步支持了这样一种观点，即V1之外的额外处理参与了透明运动分析。
