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.视觉感知显著受上下文信息的影响。典型案例为参照排斥效应（reference repulsion）：当存在明确参照刺激时，个体对某一刺激运动方向的主观报告会出现显著偏移。这类感知偏差既可能产生于感官编码阶段的早期加工，也可能反映了任务流程中相对晚期的决策相关加工过程。为厘清这两种对立的可能性，我们招募人类被试完成一项精细运动辨别任务，随后在是否呈现定向参照线的两种条件下对运动方向进行估计。当被试在参照线存在的条件下完成辨别任务，后续再在参照线移除的情况下估计运动方向时，其方向估计结果未出现偏差。然而，当被试仅观看相同刺激且仅完成估计任务，且每一试次中参照线的朝向均发生随机抖动时，其估计的运动方向会出现偏差，且与偏移后的参照线朝向高度绑定。上述结果表明，基于参照所做出的判断会受到晚期决策相关偏差的影响。将运动信息与明确参照线索信息进行整合，最终在晚期阶段对感官表征进行决策相关重加权的模型，能够解释上述实验结果。