Xiaoxin Chen¹, Benjamin Thompson^2,3,4, Daphne Maurer⁵, David Shore^5,6, Xiaoqing Gao⁷, Agnes Wong⁸, Haotian Lin⁹, Ewa Niechwiej-Szwedo¹; ¹University of Waterloo, ²School of Optometry and Vision Science, University of Waterloo, Canada, ³Centre for Eye and Vision Research, Hong Kong, ⁴University of Auckland, Liggins Institute, Auckland, New Zealand, ⁵Department of Psychology, Neuroscience & Behaviour, McMaster University, Canada, ⁶The Multisensory Mind Inc., Ontario, Canada, ⁷Center for Psychological Sciences, Zhejiang University, China, ⁸Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, and the University of Toronto, Canada, ⁹Zhongshan Ophthalmic Center, Sun Yat-Sen University, China

Binocular viewing supports efficient visuomotor task performance. Monocular viewing causes slower movement and less accuracy. The present study investigates gaze behaviour during monocular viewing during a bead threading task, which consisted of reaching, grasping, transporting, and threading a small bead onto a vertically mounted stationary needle. Participants (n=33, 19-40 [average 29.5] years old; 19 females, normal vision) completed this task under binocular, left eye and right eye viewing conditions, 15 trials each, in random orders. Monocular conditions were averaged together. An Optotrak motion capture system recorded finger movements and an EyeLink 2 eyetracker recorded gaze position. Measures of interest included fixation duration and the latency difference between eye and hand movements. Binocular advantage was quantified as: (monocular viewing - binocular viewing)/(binocular viewing). During binocular viewing, the hand movement initiated later than the eyes when reaching (120m) and simultaneously when returning (1ms). During monocular viewing condition, the hand initiated significantly later (reaching: 144ms, p=0.006; returning: 22ms, p=0.047). Despite slightly longer planning, actions were still less efficient under monocular viewing, with a 6% binocular advantage in reach duration, 7% in peak velocity, 115% in grasp duration, and 64% in thread duration. The eyes needed to fixate longer on the bead during grasping (binocular 214ms vs monocular 414ms; p<0.001), and on the needle during threading (binocular 374ms vs monocular 588ms, p<0.001). These results indicated that the slightly longer planning during monocular viewing was insufficient to support efficient task completion. The prolonged fixations suggest inefficient encoding of object features to guide task performance due to monocular viewing. Binocular input is critical for the efficient performance of manipulation tasks. Together, these data indicate that gaze behaviour during the bead threading task is sensitive to changes to viewing conditions and may be suitable for investigating gaze behaviour and visuomotor performance in patient populations with binocular deficits.

Acknowledgements: This study was funded by a Canadian Institutes of Health Research (CIHR) grant.