Solomon J A, Sperling G
NASA-Ames Research Ctr, Moffet Field, CA 94035.
Vision Res. 1994 Sep;34(17):2239-57. doi: 10.1016/0042-6989(94)90105-8.
Microbalanced stimuli are dynamic displays which do not stimulate motion mechanisms that apply standard (Fourier-energy or autocorrelational) motion analysis directly to the visual signal. In order to extract motion information from microbalanced stimuli, Chubb and Sperling [(1988) Journal of the Optical Society of America, 5, 1986-2006] proposed that the human visual system performs a rectifying transformation on the visual signal prior to standard motion analysis. The current research employs two novel types of microbalanced stimuli: half-wave stimuli preserve motion information following half-wave rectification (with a threshold) but lose motion information following full-wave rectification; full-wave stimuli preserve motion information following full-wave rectification but lose motion information following half-wave rectification. Additionally, Fourier stimuli, ordinary square-wave gratings, were used to stimulate standard motion mechanisms. Psychometric functions (direction discrimination vs stimulus contrast) were obtained for each type of stimulus when presented alone, and when masked by each of the other stimuli (presented as moving masks and also as nonmoving, counterphase-flickering masks).
given sufficient contrast, all three types of stimulus convey motion. However, only one-third of the population can perceive the motion of the half-wave stimulus. Observers are able to process the motion information contained in the Fourier stimulus slightly more efficiently than the information in the full-wave stimulus but are much less efficient in processing half-wave motion information. Moving masks are more effective than counterphase masks at hampering direction discrimination, indicating that some of the masking effect is interference between motion mechanisms, and some occurs at earlier stages. When either full-wave and Fourier or half-wave and Fourier gratings are presented simultaneously, there is a wide range of relative contrasts within which the motion directions of both gratings are easily determinable. Conversely, when half-wave and full-wave gratings are combined, the direction of only one of these gratings can be determined with high accuracy.
the results indicate that three motion computations are carried out, any two in parallel: one standard ("first order") and two non-Fourier ("second-order") computations that employ full-wave and half-wave rectification.
微平衡刺激是一种动态显示，它不会刺激那些直接对视觉信号应用标准（傅里叶能量或自相关）运动分析的运动机制。为了从微平衡刺激中提取运动信息，Chubb和Sperling[（1988年）《美国光学学会杂志》，5，1986 - 2006]提出，人类视觉系统在进行标准运动分析之前，会对视觉信号进行整流变换。当前的研究采用了两种新型的微平衡刺激：半波刺激在半波整流（有一个阈值）后保留运动信息，但在全波整流后失去运动信息；全波刺激在全波整流后保留运动信息，但在半波整流后失去运动信息。此外，还使用了傅里叶刺激，即普通的方波光栅，来刺激标准运动机制。分别在每种刺激单独呈现时，以及被其他每种刺激（以移动掩蔽和非移动的反相闪烁掩蔽形式呈现）掩蔽时，获取了每种刺激的心理测量函数（方向辨别与刺激对比度）。
在有足够对比度的情况下，所有三种类型的刺激都能传达运动信息。然而，只有三分之一的人能感知到半波刺激的运动。观察者处理傅里叶刺激中包含的运动信息的效率略高于全波刺激中的信息，但处理半波运动信息的效率要低得多。移动掩蔽在阻碍方向辨别方面比反相掩蔽更有效，这表明部分掩蔽效应是运动机制之间的干扰，部分发生在更早的阶段。当同时呈现全波和傅里叶光栅或半波和傅里叶光栅时，在很宽的相对对比度范围内，两种光栅的运动方向都很容易确定。相反，当半波和全波光栅组合时，只能高精度地确定其中一种光栅的方向。
结果表明进行了三种运动计算，其中任意两种是并行的：一种是标准的（“一阶”）计算，另外两种是非傅里叶的（“二阶”）计算，分别采用全波和半波整流。
