Time is needed for memory to be biased toward an ensemble average

[摘要] It has been shown that memory of an individual item is biased toward an ensemble average (Brady & Alvarez, 2011; Lew & Vul, 2015). Here we investigated how this bias changes over time by using an orientation estimation task. Participants were presented with 20 oriented white bars for 200 ms on a gray background. In each trial, the stimuli had five orientations that differed by 0, −15, +15, −30, and +30 degrees from a randomly selected orientation, and each orientation was uniformly sampled four times. These 20 stimuli were then randomly presented within an imaginary 4 × 5 grid. The participants had to remember those bars and recall the orientation of a target, which was cued with a circular contour. This cue was displayed at one of three different times. In one condition, the stimuli and the cue were simultaneously presented; in other two conditions, the cue was presented 500 ms or 1000 ms after the stimuli onset. Estimation phase started 1500 ms after the stimuli onset such that a randomly oriented probe appeared within the circular cue, and the participants reported the remembered orientation of the target by adjusting the probe orientation. Importantly, the target orientation was either the mean orientation of the 20 stimuli or ±15 degrees from the mean. When the cue was simultaneously presented with the stimuli, the remembered orientation of the target was similar to its physical orientation. However, when the cue was presented 500 ms or 1000 ms after the stimuli onset, the remembered orientation was biased toward the mean orientation of the 20 stimuli. These results suggest that the memory representation is gradually biased toward an ensemble average over time.

[学科分类] 眼科学