What can half a million change detection trials tell us about visual working memory?

Visual working memory (VWM) represents the surrounding world in an active and accessible state, but its capacity is severely limited. To better understand VWM and its limits, we collected data from over 3,800 participants in the canonical change detection task. This unique population-level data-set sheds new light on classic debates regarding VWM capacity. First, the result supported a view of VWM as an active process, as manifested by the fact that capacity estimates were not stable across set-sizes, but rather lower for the larger set-size. Another support for this notion came from the tight connection capacity estimates had with a measure of attentional control. Together, the data suggested that individual differences in capacity do not reflect only differences in storage-size, but differences in the efficiency of using this storage. Second, we found a response bias such that subjects are more likely to respond that the probed item changed, and this criterion bias was further shifted as the set-size increased. These findings are naturally explained by a slot-like theory arguing that when load exceeds capacity, certain items remain completely outside of VWM (instead of all items being represented in lower resolution), therefore causing subjects to perceive them as different from VWM contents even when they are unchanged. Additionally, we found that the pattern of d' also confirmed the predictions of a slot-like view of VWM, such that some items are represented with high fixed resolution and others are not represented at all, although this finding is based on two measures with very different underlying assumptions. We also discuss how flexible-resource views can accommodate these results. Moreover, comparing performance between the first and last trials demonstrated no evidence for proactive interference as the driving factor of capacity limitations. We provide further details regarding the distribution of individual capacity, the relations between capacity and demographic variables, and the spatial prioritization of the items.