No Evidence for an Object Working Memory Capacity Benefit with Extended Viewing Time

Abstract

Visual working memory is the ability to hold visual information temporarily in mind. A key feature of working memory is its starkly limited capacity, such that only a few simple items can be remembered at once. Prior work has shown that this capacity limit cannot be circumvented by providing additional encoding time, whether providing just 200 ms or up to 1300 ms, capacity is still limited to only three to four items. In contrast, Brady et al. (2016) hypothesized that real-world objects, but not simple items used in prior research, benefit from additional encoding time and are not subject to traditional capacity limits. They supported this hypothesis with results from both behavior and the contralateral delay activity (CDA), an EEG marker of working memory storage, and concluded that familiar, complex stimuli are necessary to observe encoding time effects. Here, we conducted three replications of Brady et al.’s key manipulation with a larger number of human participants and more trials per condition. We failed to replicate their primary behavioral result (objects benefit more than colors from additional encoding time) and failed to observe an object-specific increase in the CDA. Instead, we found that encoding time benefitted both simple color items and real-world objects, in contrast to both the findings by Brady et al., and some prior work on this topic. Overall, we observed no support for the hypothesis that real-world objects have a different capacity than colored squares. We discuss the implications of our findings for theories of visual working memory (VWM).

Significance Statement A long-standing debate in visual working memory (VWM) has centered on the limits of working memory. VWM is thought to rely on a fixed pool of resources, but recent work by Brady et al. (2016) suggested that capacity is higher for real-world objects compared with simple stimuli. Our study attempts to replicate this result. Surprisingly, we found a performance increase for both simple and real-world stimuli at longer encoding times, but a complementary finding was not observed in the contralateral delay activity (CDA). Based on this, our data show no specific evidence for a capacity benefit for real-world items.