O'Toole A J, Walker C L
School of Human Development, University of Texas at Dallas, Richardson 75083-0688, USA.
Percept Psychophys. 1997 Feb;59(2):202-18. doi: 10.3758/bf03211889.
We examined the generality of the claim that stereoscopic disparity is detectable in parallel across the visual field. Using a search paradigm with random-dot stereograms, we varied the relative disparity of target and distractor items. When both target and distractors had crossed disparities, both search functions (i.e., target in front of distractors and target behind distractors) were linear with positive slopes. When both target and distractors had uncrossed disparities, the pattern of results depended upon whether the target was in front of or behind the distractors-specifically, when the target was in front of the distractors, search functions were similar to those seen for "crossed" search, but when the target was behind the distractors, a nonlinear search function was found. Finally, when the target and distractors straddled the plane of fixation, a nonlinear search function was found when the target was in front of the distractors; however, when the target was behind the distractors, a linear search function with a large positive slope was found. We show that the nonlinear search functions are consistent with the effects of an intervening global surface percept. We also show that the size of the stimulus display may be a factor in some relative depth cases. Additionally, we replicate Steinman's (1987) finding that search is parallel when the distractors are located at the plane of fixation and the target disparity is crossed, eliminating monocular and spatial cues to target presence that may have been present in his original study. In a final control experiment, we showed that reaction times did not increase with set size when observers performed another kind of perceptual task on similar random-dot stereogram displays. This eliminates the possibility that some of the results obtained here can be explained by increases in the difficulty of perceiving/fusing the stimuli when the number of distractors is increased.
我们检验了关于立体视差可在整个视野中并行检测到这一说法的普遍性。使用带有随机点立体图的搜索范式，我们改变了目标和干扰项的相对视差。当目标和干扰项都具有交叉视差时，两种搜索函数（即目标在干扰项之前和目标在干扰项之后）都是具有正斜率的线性函数。当目标和干扰项都具有非交叉视差时，结果模式取决于目标是在干扰项之前还是之后——具体而言，当目标在干扰项之前时，搜索函数类似于“交叉”搜索时看到的函数，但当目标在干扰项之后时，发现了非线性搜索函数。最后，当目标和干扰项跨越固定平面时，当目标在干扰项之前时发现了非线性搜索函数；然而，当目标在干扰项之后时，发现了具有大正斜率的线性搜索函数。我们表明，非线性搜索函数与中间全局表面感知的效果一致。我们还表明，刺激显示的大小可能是某些相对深度情况中的一个因素。此外，我们重复了斯坦曼（1987年）的发现，即当干扰项位于固定平面且目标视差为交叉时，搜索是并行的，消除了他原始研究中可能存在的目标存在的单眼和空间线索。在最后一个对照实验中，我们表明，当观察者在类似的随机点立体图显示上执行另一种感知任务时，反应时间不会随着集合大小的增加而增加。这消除了此处获得的一些结果可以通过增加干扰项数量时感知/融合刺激的难度增加来解释的可能性。
