Evidence of Gradual Loss of Precision for Simple Features and Complex Objects in Visual Working Memory

Previous studies have suggested that people can maintain prioritized items in visual working memory for many seconds, with negligible loss of information over time. Such findings imply that working memory representations are robust to the potential contaminating effects of internal noise. However, once visual information is encoded into working memory, one might expect it to inevitably begin degrading over time, as this actively maintained information is no longer tethered to the original perceptual input. Here, we examined this issue by evaluating working memory for single central presentations of an oriented grating, color patch, or face stimulus, across a range of delay periods (1, 3, 6, or 12 s). We applied a mixture-model analysis to distinguish changes in memory precision over time from changes in the frequency of outlier responses that resemble random guesses. For all 3 types of stimuli, participants exhibited a clear and consistent decline in the precision of working memory as a function of temporal delay, as well as a modest increase in guessing-related responses for colored patches and face stimuli. We observed a similar loss of precision over time while controlling for temporal distinctiveness. Our results demonstrate that visual working memory is far from lossless: while basic visual features and complex objects can be maintained in a quite stable manner over time, these representations are still subject to noise accumulation and complete termination. Public Significance Statement The ability to retain visual information over brief delays is critical for accurate visual performance. Numerous studies have claimed that items in visual working memory are immune to temporal decay. This is surprising, given that information maintained in working memory is no longer tethered to the original perceptual input. One could rightfully wonder how any biological system would be able to achieve perfect retention under such circumstances. Here, we show that working memory for individual orientations, colors, and faces, undergoes gradual decay over time, even when occurrences of complete memory failure are taken into account. Our statistical and model comparison analyses provide compelling evidence that information represented in visual working memory accumulates noise over time, leading to a gradual but inevitable loss of visual precision.