Data from: Do perceptual biases emerge early or late in visual processing?

Visual perception is strongly influenced by contextual information. A good example is reference repulsion, where subjective reports about the direction of motion of a stimulus are significantly biased by the presence of an explicit reference. These perceptual biases could arise early, during sensory encoding, or alternatively they may reflect decision-related processes occurring relatively late in the task sequence. To separate these two competing possibilities, we asked (human) subjects to perform a fine motion-discrimination task and then estimate the direction of motion in the presence or absence of an oriented reference line. When subjects performed the discrimination task with the reference, but subsequently estimated motion direction in its absence, direction estimates were unbiased. However, when subjects viewed the same stimuli but performed the estimation task only, with the orientation of the reference line jittered on every trial, the directions estimated by subjects were biased and yoked to the orientation of the shifted reference line. These results show that judgments made relative to a reference are subject to late, decision-related biases. A model in which information about motion is integrated with that of an explicit reference cue, resulting in a late, decision-related re-weighting of the sensory representation, can account for these results.

视觉感知过程强烈受上下文信息的调控。典型例证为参考排斥效应（Reference Repulsion）：当存在显性参考刺激时，个体对某一运动刺激的运动方向所做的主观报告将出现显著偏差。此类感知偏差既可能产生于感觉编码阶段的早期，也可能反映了任务流程后期与决策相关的认知加工过程。为区分这两种竞争性假说，我们设计了两组实验：第一组要求人类被试先完成一项带有定向参考线的精细运动辨别任务，随后在无参考线的条件下估计运动方向；第二组中被试仅观看相同刺激并仅完成运动方向估计任务，且每一试次中参考线的朝向均发生随机抖动。实验结果显示，第一组被试的方向估计结果并无偏差；而第二组被试估计的运动方向会出现显著偏差，且与偏移后的参考线朝向绑定一致。上述结果表明，以参考为基准做出的判断会受到后期与决策相关的偏差影响。我们构建的计算模型将运动信息与显性参考线索的信息进行整合，最终在决策阶段对感觉表征进行后期的决策相关重加权，该模型能够很好地解释上述实验结果。