Neural correlates of a load-dependent decline in visual working memory.

Previous studies have shown that a rate of temporal decline in visual working memory (vWM) highly depends on a number of memory items. When people retain the information of many (≥ 4) stimuli simultaneously, their memory representations are fragile and rapidly degrade within 2-3 s after an offset (called the "competition" among memory items). When a memory load is low (1 or 2 items), in contrast, the fidelity of vWM is preserved for a longer time because focused attention to the small number of items prevents the temporal degradation. In the present study, we explored neural correlates of this load-dependent decline of vWM in the human brain. Using electroencephalography and a classical change-detection task, we recorded neural measures of vWM that have been reported previously, such as the contralateral delay activity (CDA) and a suppression of alpha power (8-12 Hz). Results indicated that the load-dependent decline of vWM was more clearly reflected in the change in power and speed of alpha/beta rhythm than CDA, suggesting a close relationship of those signals to an attention-based preservation of WM fidelity.