Serial dependency bias as memory averaging

Abstract

It has been established that perceptual reports are influenced by previously reported percepts, a phenomenon described as 'serial dependency in perception'. For example, the reported orientation of a line grating is attracted towards the orientation reported in the previous trial. This process presumably promotes perceptual stability in a noisy and dynamic visual world by integrating visual information sampled from the same object at different points in time. Despite a recent surge in studies illustrating serial dependency effects, it remains unclear whether these biases arise during perception (i.e., stimulus encoding), or within memory (i.e., stimulus maintenance). To distinguish between these possibilities, we sequentially presented four oriented gratings in an n-back working memory task. Participants were retro-actively cued which of the four orientations they should reproduce. In addition to the classic serial dependency effect, our data showed that reports were also biased by subsequently presented orientations. When, for example, the second item in the sequence was the target, its reported orientation was not only influenced by the first item but also by the third and fourth items. This finding excludes the possibility that serial dependency biases arise solely during encoding, since reported stimuli were already stored in memory at the time subsequent, influencing stimuli were presented. Based on data from three studies we propose a new model of serial bias in vision, describing the behavioral report of a perceived target as the result of an attentionally modulated, weighted average between the actual target, task-relevant information preceding and succeeding the target, as well as previous behavioral reports. Supplementary materials such as pre-prints, data, stimulus, and analysis scripts can be found at https://osf.io/54abr/?view_only=2f67d292ed9e4ed6bc731da09b624069