Abstract
People often remember visual information over brief delays while actively engaging with ongoing inputs from the surrounding visual environment. Depending on the situation, one might prioritize mnemonic contents (i.e. remembering details of a past event), or preferentially attend sensory inputs (i.e. watching traffic while crossing a street). Previous fMRI work has shown that early sensory regions can simultaneously represent both mnemonic and passively viewed sensory information. Here we test the limits of such simultaneity by manipulating attention towards sensory distractors during working memory. Participants (N=6) remembered the orientation of a briefly presented (500ms) target grating while a distractor grating (11s) was shown during the middle portion of a 15s delay. Subjects reported the target by rotating a dial (3s). Target and distractor orientations were selected randomly and independent of one another. Critically, the distractor grating was continuously contrast-reversing at 4Hz, and on every trial, there were 2–4 brief (250ms) and subtle changes in its contrast (decrease or increase) and its orientation (counter-clockwise or clockwise). In three randomly interleaved conditions, participants were cued to either ignore the distractor, detect distractor-contrast changes, or detect distractor-orientation changes. Behavioral performance on the distractor-contrast and distractor-orientation tasks was equated via a staircase. Despite sensory stimulation being matched in all three conditions, memory representations differed strongly throughout the visual hierarchy: Fidelity was highest when the distractor was ignored, intermediate when participants attended distractor-contrast, and virtually absent when participants attended distractor-orientation during the delay. This is juxtaposed with representations of the sensed distractor during the delay: Fidelity was highest when attending distractor-orientation, intermediate when attending distractor-contrast, and lowest when ignoring the distractor (even absent in parietal regions). These data imply that any trade-offs between memory and sensory representations are due to changes in attentional priority as opposed to just the presence or absence of concurrent input.
Acknowledgement: Marie Sklodowska-Curie Grant Agreement No 743941 to RLR