Ferrera V P, Wilson H R
Department of Ophthalmology, University of Chicago, IL 60637.
Vision Res. 1991;31(5):877-93. doi: 10.1016/0042-6989(91)90154-w.
When two cosine gratings drifting in different directions are superimposed they can form a coherently moving two-dimensional pattern (plaid) whose resultant speed is related to the component velocities by a geometric construction known as the intersection-of-constraints (IOC). When measured against a standard which has the same spatial frequency as its components, a plaid always appears to move slower than the IOC prediction. However, the perceived speed is generally faster than would be predicted if speed were judged based on the temporal frequency of either the components or the nodes of the plaid. On the other hand, when the standard has the same spatial period as the nodes, the plaid appears to move at the same rate as the predicted IOC resultant. Furthermore, a grating with the same spatial period as the nodes appears to move slower than a grating at the component spatial frequency, just the plaid does. It is therefore likely that speed is encoded similarly for both gratings and plaids, and that the perceived speed of both is determined by the spatial periodicity of the pattern. We have previously classified 2D moving patterns as either type I (resultant lies between component directions) or type II (resultant outside of components). We find that the perceived speed of both types can be accounted for on the basis of the nodal spatial period. Finally we present a model for velocity coding which is based on the responses of spatio-temporal mechanisms.
当两个沿不同方向漂移的余弦光栅叠加时，它们可以形成一个连贯移动的二维图案（方格图案），其合成速度通过一种称为约束交集（IOC）的几何结构与分量速度相关。当与具有与其分量相同空间频率的标准进行比较测量时，方格图案似乎总是比IOC预测的移动得慢。然而，感知到的速度通常比基于分量或方格图案节点的时间频率判断速度时预测的要快。另一方面，当标准与节点具有相同的空间周期时，方格图案似乎以与预测的IOC合成速度相同的速率移动。此外，与节点具有相同空间周期的光栅似乎比具有分量空间频率的光栅移动得慢，就像方格图案一样。因此，速度对于光栅和方格图案的编码可能类似，并且两者的感知速度都由图案的空间周期性决定。我们之前将二维移动图案分类为I型（合成方向位于分量方向之间）或II型（合成方向在分量方向之外）。我们发现，这两种类型的感知速度都可以根据节点空间周期来解释。最后，我们提出了一个基于时空机制响应的速度编码模型。
