Abstract
Competition between simultaneously presented visual stimuli lengthens reaction time and reduces both the BOLD response and neural firing. In contrast, conditions of sequential presentation have been assumed to be free from competition. Here we manipulated the spatial proximity of stimuli (Near versus Far conditions) to examine the effects of simultaneous and sequential competition on different measures of working memory (WM) for colour. With simultaneous presentation, the measure of WM precision was significantly lower for Near items, and participants reported the colour of the wrong item more often. These effects were preserved when the second stimulus immediately followed the first, disappeared when they were separated by 500 ms, and were partly recovered (evident for our measure of mis-binding but not WM precision) when the task was altered to encourage participants to maintain the sequentially presented items together in WM. Our results show, for the first time, that competition affects the measure of WM precision, and challenge the assumption that sequential presentation removes competition.
Highlights
Objects in a visual scene compete for neural coding during perception
Our findings indicate that the influence of competition extends to the measure of working memory (WM) precision
For the first time, that items presented within close spatial proximity are reported with lower WM precision, presumably due to greater competition within the visual cortex
Summary
Objects in a visual scene compete for neural coding during perception. Single cell recordings[1,2,3] and fMRI results indicate mutual suppression of items within the same receptive field (RF)[4, 5]. The effects of competitive interactions between stimuli are apparent behaviourally, with greater feature similarity between targets and distractors slowing visual search performance e.g. ref. 9), who reveal greater WM capacity for eight items presented in two sequential displays, compared to simultaneous presentation of all items. This suggests more items can be held in WM when competition between stimuli is reduced. We do not address whether items compete within WM, we examine whether the effects of competitive-interactions (irrespective of the stage at which they occur) can be observed in the measure of WM precision. Crowding effects reveal another example of substantial interference in identifying one stimulus when other stimuli with similar features are nearby[20]
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