Johnston A, Wright M J
Vision Res. 1986;26(7):1099-109. doi: 10.1016/0042-6989(86)90044-1.
The apparent velocity of peripheral, drifting sinusoidal gratings was measured as a function of eccentricity and viewing distance. Gratings appeared to move more slowly in the periphery. Apparent velocities in fovea and periphery could be matched by an appropriate spatial scaling of peripheral gratings. This scaling factor provides a psychophysical measure of the changing spatial grain of the visual system with eccentricity. Scaling factors were found to be the same for lower threshold of motion and for velocity matching with standard gratings of 2 and 6 Hz. The finding generalised over a range of standard temporal frequencies (less than 7 Hz) and spatial frequencies (1.2-9 c/deg). The psychophysically determined scaling factors were found to be proportional to the square root of macaque mean cortical receptive field area as a function of eccentricity. The data support a ratio strategy for encoding motion in which motion information is expressed relative to the changing spatial grain of the visual system. Locations for the apparent identity of physically identical grating motion fell along a straight line in space, prompting an explanation of these visual field effects in terms of the acquisition of environmental information from optic flow.
测量了周边漂移正弦光栅的视在速度，它是离心率和观察距离的函数。光栅在周边似乎移动得更慢。通过对周边光栅进行适当的空间缩放，可以使中央凹和周边的视在速度相匹配。这个缩放因子提供了视觉系统空间粒度随离心率变化的心理物理学测量。发现运动阈值下限以及与2赫兹和6赫兹标准光栅的速度匹配的缩放因子是相同的。这一发现适用于一系列标准时间频率（小于7赫兹）和空间频率（1.2 - 9周/度）。经心理物理学测定的缩放因子被发现与猕猴平均皮层感受野面积的平方根成正比，作为离心率的函数。这些数据支持一种用于编码运动的比率策略，其中运动信息是相对于视觉系统不断变化的空间粒度来表达的。物理上相同的光栅运动的视在同一性位置在空间中沿直线分布，这促使人们根据从光流中获取环境信息来解释这些视野效应。
