The precision of visual working memory (VWM) representations decreases as time passes. It is often assumed that VWM decay is random and caused by internal noise accumulation. However, forgetting in VWM could occur systematically, such that some features deteriorate more rapidly than others. There exist only a few studies testing these two models of forgetting, with conﬂicting results. Here, decay of features in VWM was thoroughly tested using signal detection theory methods: psychophysical classiﬁcation images, internal noise estimation, and receiver operant characteristic (ROC). A modiﬁed same–diﬀerent memory task was employed with two retention times (500 and 4000 ms). Experiment 1 investigated VWM decay using a compound grating memory task, and Experiment 2 tested shape memory using radial frequency patterns. Memory performance dropped some 15% with increasing retention time in both experiments. Interestingly, classiﬁcation images showed virtually indistinguishable weighting of stimulus features at both retention times, suggesting that VWM decay is not feature speciﬁc. Instead, we found a 77% increase in stimulus-independent internal noise at the longer retention time. Finally, the slope of the ROC curve plotted as z-scores was shallower at the longer retention time, indicating that the amount of stimulus-independent internal noise increased. Together these ﬁndings provide strong support for the idea that VWM decay does not result from a systematic loss of some stimulus features but instead is caused by uniformly increasing random internal noise.
Aided by a grant from the Jenny and Antti Wihuri Foundation (CK). Open access funded by Helsinki University Library.
- 515 Psykologia