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.

视觉感知过程显著受情境信息的影响。其中典型案例为参照排斥效应（reference repulsion）：当存在明确参照线索时，被试对刺激运动方向的主观报告将出现显著的定向偏差。这类感知偏差可能产生于感官编码阶段的早期加工，也可能反映任务序列后期与决策相关的加工过程。为区分这两种互斥的可能性，我们招募人类被试完成两项实验任务：先执行一项精细运动辨别任务，随后在有或无定向参照线的条件下估计运动方向。当被试先在有参照线的条件下完成辨别任务，随后在无参照线的条件下估计运动方向时，其运动方向估计结果未出现偏差。但当被试仅观看相同刺激并仅执行估计任务，且每一试次中参照线的定向均随机抖动时，其估计的运动方向将出现偏差，且偏差方向与偏移后的参照线定向保持一致。上述结果表明，以参照为基准做出的判断会受到后期决策相关加工带来的偏差影响。若构建一个将运动信息与明确参照线索信息进行整合的模型，该模型会在后期对感官表征进行与决策相关的重加权操作，则可解释上述实验结果。