Swindale N V
Department of Ophthalmology, University of British Columbia, Vancouver, Canada.
Vis Neurosci. 1995 Sep-Oct;12(5):805-17. doi: 10.1017/s0952523800009378.
This paper examines how the responses of cells in area 17 of the cat vary as a function of the vernier offset between a bright and a dark bar. The study was prompted by the finding that human vernier acuity is reduced for bars or edges of opposite contrast sign (Mather & Morgan, 1986; O'Shea & Mitchell, 1990). Both simple and complex cells showed V-shaped tuning curves for reverse contrast stimuli: i.e. response was minimum at alignment, and increased with increasing vernier offset. For vernier bars with the same contrast sing, v-shaped tuning curves were found, as reported earlier (Swindale & Cynader, 1986). Sensitivity to offset was inversely correlated in the two paradigms. However, complex cells with high sensitivity to offsets in a normal vernier stimulus were significantly less sensitive to offsets in reverse contrast stimuli. A cell's response to a vernier stimulus in which both bars are bright can be predicted by the shape of its orientation tuning curve, if the vernier stimulus is approximated by a single bar with an orientation equal to that of a line joining the midpoints of the two component bars (Swindale & Cynader, 1986). This approximation did not hold for the reverse contrast condition: orientation tuning curves for compound bars were broad and shallow, rather than bimodal, with peaks up to 40 deg from the preferred orientation. Results from simple cells were compared with predictions made by a linear model of the receptive field. The model predicted the [symbol: see text]-shaped tuning curves found for reverse contrast stimuli. It also predicted that absolute values of tuning slopes for vernier offsets in reverse contrast stimuli might sometimes be higher than with normal stimuli. This was observed in some simple cells. The model was unable to explain the shape of orientation tuning curves for compound bars, nor could it explain the breakdown of the equivalent orientation approximation.
本文研究了猫17区细胞的反应如何随亮条和暗条之间的游标偏移而变化。该研究是由以下发现引发的：对于具有相反对比度符号的条或边缘，人类游标敏锐度会降低（马瑟和摩根，1986年；奥谢和米切尔，1990年）。简单细胞和复杂细胞对反向对比度刺激均呈现V形调谐曲线：即对齐时反应最小，并随着游标偏移增加而增强。对于具有相同对比度符号的游标条，如先前报道（斯温代尔和西纳德，1986年），发现了V形调谐曲线。在这两种范式中，对偏移的敏感度呈负相关。然而，在正常游标刺激中对偏移具有高敏感度的复杂细胞，对反向对比度刺激中的偏移敏感度显著降低。如果将游标刺激近似为一个方向等于连接两个组成条中点的线的方向的单个条，那么细胞对两个条均为亮的游标刺激的反应可以通过其方向调谐曲线的形状来预测（斯温代尔和西纳德，1986年）。这种近似在反向对比度条件下不成立：复合条的方向调谐曲线宽且浅，而非双峰，峰值偏离首选方向可达40度。将简单细胞的结果与感受野线性模型的预测进行了比较。该模型预测了反向对比度刺激中发现的V形调谐曲线。它还预测，反向对比度刺激中游标偏移的调谐斜率绝对值有时可能高于正常刺激。在一些简单细胞中观察到了这一点。该模型无法解释复合条方向调谐曲线的形状，也无法解释等效方向近似的失效。
