The breadth of retrospective spatial attention is modulated by the vividness of the trace in visual short-term memory

The duration and vividness of the memory trace in visual short-term memory stages remains a debated issue in consciousness studies. The present study sought to investigate which is the fate of a trace stored in visual short-term memory when time passes and how retrospective spatial attention interacts with this process. Twenty subjects performed a change detection task in which the focus of attention during encoding was manipulated using a spatial pre-cue (i.e., left or right arrow). After the presentation of the memory array, the appearance of the retro-cue could either direct internal attention in accordance with the side of the screen indicated by the pre-cue (i.e., valid) or to the opposite side (i.e., invalid). In both valid and invalid conditions, the retro-cue could point toward a probe item that was placed at the extreme left or right (i.e., peripheral) or at the mid-left or mid-right (i.e., central) part of the memory array. Results showed differences in accuracy at 150 ms retro-cue delay for central and peripheral items in both valid and invalid conditions, while at 600 ms and 1200 ms retro-cue delay differences in central and peripheral items were only found for the valid condition. These results may give insights on the mechanism of retrospective spatial attention, suggesting that when time passes, the memory trace in short-term memory start to fade out, the breadth of internal attention progressively narrows, and it is no longer possible to retrieve items that are outside the focus of attention.