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到上下文信息的影响。典型例证为参考排斥效应（reference repulsion）：当存在显性参考物时，个体对刺激物运动方向的主观报告将出现显著偏差。此类感知偏差既可产生于感官编码的早期阶段，也可能反映任务序列后期发生的决策相关认知过程。为区分这两种竞争性假说，我们招募人类被试完成一项精细运动辨别任务（fine motion-discrimination task），随后在有或无定向参考线的条件下估算运动方向。当被试先在存在参考线的条件下完成辨别任务，再在无参考线的条件下估算运动方向时，其方向估算结果无明显偏差。然而，当被试仅观看相同刺激物且仅执行估算任务，且每一试次（trial）中参考线的朝向均随机抖动时，其估算的运动方向将出现偏差，且与偏移后的参考线朝向同步匹配。上述结果表明，以参考物为参照作出的判断，会受到后期决策相关偏差的影响。若构建一个将运动信息与显性参考线索信息进行整合的模型，并在后期通过决策相关过程对感官表征进行重新加权，则可解释上述实验结果。