Serrano-Pedraza Ignacio, Hogg Ellen L, Read Jenny C A
Faculty of Psychology, Departmernt of Basic Psychology I, Complutense University of Madrid, Campusde Somosaguas, Madrid, Spain.
J Vis. 2011 Feb 3;11(2):3. doi: 10.1167/11.2.3.
At high contrast, duration thresholds for motion direction discrimination deteriorate with increasing stimulus size. This counterintuitive result has been explained by the center-surround antagonism present in the neurons of visual area MT. Conversely, at very low contrast, direction discrimination improves with increasing size, a result that has been explained by spatial summation. In this investigation, we study the effects of stimulus shape and contrast on center-surround antagonism. Using adaptive Bayesian staircases, we measured duration thresholds of 5 subjects for vertically oriented Gabor patches of 1 cycle/deg with two types of oval Gaussian windows, one vertically elongated (Sx = 0.35, Sy = 2.5 deg) and other horizontally elongated (Sx = 2.5, Sy = 0.35 deg) moving rightward or leftward at a speed of 2 deg/s. We found that at high contrast (92%) duration thresholds were lower for vertically than horizontally elongated windows. However, at low contrast (2.8%), we found that duration thresholds were lower for horizontally than vertically elongated windows. These asymmetric results mirror the spatial non-homogeneity of the antagonistic surround found in MT neurons and suggest that the underlying center-surround antagonism is stronger along the direction of motion.
在高对比度下，运动方向辨别所需的持续时间阈值会随着刺激大小的增加而恶化。这一违反直觉的结果已通过视觉区域MT神经元中存在的中心-外周拮抗作用得到解释。相反，在极低对比度下，方向辨别能力会随着大小的增加而提高，这一结果已通过空间总和得到解释。在本研究中，我们研究了刺激形状和对比度对中心-外周拮抗作用的影响。使用自适应贝叶斯阶梯法，我们测量了5名受试者对具有两种椭圆形高斯窗口的1周期/度垂直定向Gabor斑块的持续时间阈值，一种是垂直拉长的（Sx = 0.35，Sy = 2.5度），另一种是水平拉长的（Sx = 2.5，Sy = 0.35度），以2度/秒的速度向右或向左移动。我们发现，在高对比度（92%）下，垂直拉长窗口的持续时间阈值低于水平拉长窗口。然而，在低对比度（2.8%）下，我们发现水平拉长窗口的持续时间阈值低于垂直拉长窗口。这些不对称结果反映了MT神经元中拮抗外周的空间非均匀性，并表明潜在的中心-外周拮抗作用在运动方向上更强。
