Nikolaev, A. R. | bioRxiv Science

bioRxiv2019

Neural Correlates of Task-related Refixation Behaviour

Information uptake during scene viewing under free viewing conditions is crucially determined by the scanning plan. This plan is determined both by top-down and bottom-up factors. To capture top-down factors affecting saccade planning, we compared EEG between first fixations and refixations on items varying in task-relevance. First fixations and refixations impose different working memory costs because first fixations involve encoding of new items whereas refixations involve rehearsal of existing items in working memory. These memory requirements also differ with the task-relevance of the item being encoded. Together, these two factors of task-relevance and memory processes related to refixation behavior would affect saccade planning. In a visual task involving search and memorization of multiple targets, we compared saccade-related potentials (SRPs) between first fixations and refixations for task-relevant (target) and task-irrelevant (distractor) items. We assessed the interval preceding a saccade away from the fixation of interest. Studying this presaccadic interval revealed how mechanisms related to saccade preparation are affected by task-relevance and refixation behavior. We found higher SRP amplitudes for first fixations than refixations over the occipital region for task-relevant items only. Our findings indicate that saccade planning is modulated by both task-relevance of an item and working memory load.

neuroscience↗

bioRxiv2019

Revising the scanning plan for continued visual exploration: the neurophysiology of refixation-related behavior

Eye tracking studies suggest that refixations, fixations to locations previously visited, serve to recover information lost or missed during earlier exploration of a visual scene. These studies have largely ignored the role of precursor fixations, previous fixations on locations the eyes return to later. We consider the possibility that preparations to return later are already made during precursor fixations. This would mark precursor fixations as a special category of fixations, i.e., distinct in neural activity from other fixation categories such as refixations and fixations to locations visited only once. To capture the neural signals associated with fixation categories, we analyzed EEG and eye movement recorded simultaneously in a free-viewing contour search task. We developed a methodological pipeline involving regression-based deconvolution modeling, allowing our analyses to account for overlapping EEG responses due to the saccade sequence and other oculomotor covariates. We found that precursor fixations were preceded by the largest saccades among the fixation categories. Independently of the effect of saccade length, EEG amplitude was enhanced in precursor fixations compared to the other fixation categories 200-400 ms after fixation onsets, most noticeably over the occipital areas. We concluded that precursor fixations play a pivotal role in visual perception, marking the continuous occurrence of transitions between exploratory and exploitative modes of eye movement in natural viewing behavior.

neuroscience↗