Extraretinal information provided by smooth pursuit is crucial for accurate hand tracking

When tracking or reaching a visual target with the hand, retinal information is key to guide the hand. Although the contribution of extraretinal signals associated with saccades is established for reaching movements, less is known about extraretinal contribution during manual tracking in which smooth pursuit dominates. To fill this gap, we conducted a study in which eye and hand tracking performance were compared across multiple conditions in which eye and hand movements performed similar/dissimilar tasks. In the SINGLE condition, participants (n=26) were asked to track a unique target with both eyes and hand. In the DOUBLE condition, their eyes and hand had to track separate targets that followed the same trajectory but displayed on separate hemifields. In the FIX condition, participants tracked one target with the hand while fixating eyes away from that target. We reasoned that if extraretinal information is key for manual tracking, it should be less altered in SINGLE and DOUBLE than FIX. Indeed, results showed that not only manual tracking was better in DOUBLE than FIX, but was nearly equivalent to SINGLE. Surprisingly, foveating the target provided only modest benefits to manual tracking. Finally, analyses confirmed that smooth pursuit contributed more than saccades to overall eye movements, making it the primary contributor to extraretinal information. Taken together, these results show that foveating the target is not mandatory for accurate manual tracking as long as eyes and hand perform congruent tracking/motion, and speak for a key role of extraretinal information provided by smooth pursuit.