Rhythmic Sampling and Competition of Target and Distractor Representations in Visual Sensory Memory

Recent studies suggest that sustained visual attention operates rhythmically, as if the visual system periodically samples stimuli in the environment. Here we present evidence for rhythmic sampling of internal representations of targets and distractors up to one second after visual stimulation offset. Twenty participants performed an anticipatory object-based visual attention task involving a short-lasting (50 msec) target object image. This task was made more challenging by the overlaid presentation of a distractor object image. We conducted a decoding analysis on stimulus-evoked EEG to measure target and distractor information over the stimulus epoch, which extended almost 1000 msec beyond the visual stimulus offset. We found that the magnitudes of target and distractor information represented in brain activity after the offset of the visual stimuli oscillated in the theta frequency range (4-8 Hz). This oscillatory period accords with previous characterizations of rhythmic attentional sampling of continuously visually presented stimuli. Moreover, greater target-distractor theta band phase differences correlated with improved task performance. Our findings show that: 1. Attention separately samples target and distractor representations in sensory memory; 2. These separately sampled streams of information may mutually inhibit one another; and 3. Target discrimination improves when target and distractor sampling rhythms are desynchronized.