Ocular working memory signals are flexible to behavioral priority and subjective imagery strength

Abstract

The pupillary light response was long considered a brainstem reflex, outside of cognitive influence. However, newer findings indicate pupil dilation (and eye movements) can reflect content in working memory (WM). These findings may reshape understanding of ocular and WM mechanisms, but it is unclear whether the signals are artifactual or functional to WM. Here, we ask whether peripheral and oculomotor WM signals are sensitive to the task-relevance or 'attentional state' of memoranda. During eye-tracking, human participants saw both dark and bright WM stimuli, then were retroactively cued to the most likely to be tested item. Critically, we manipulated the attentional priority among items by varying the cue reliability across blocks. We confirmed previous findings that remembering darker items is associated with larger pupils, and that gaze is biased toward cued item locations. Moreover, we discovered that pupil and eye movement responses were influenced differently by WM item relevance. Feature-specific pupillary effects emerged only for highly prioritized WM items but were eliminated when cues were less reliable, and pupil effects also increased with self-reported visual imagery strength. Conversely, gaze position veered toward the cued item location, regardless of cue reliability. However, biased microsaccades occurred at a higher frequency when cues were reliable, though only during a limited post-cue time window. Therefore, peripheral sensorimotor processing is sensitive to the task-relevance or functional state of internal WM content, but pupillary and eye movement WM signals show distinct profiles. These results highlight potential roles for early visual processing in maintaining multiple WM content dimensions.