Scott Watamaniuk^1,2, Devashish Singh², Arvind Chandna², Stephen Heinen²; ¹Wright State University, ²The Smith-Kettlewell Eye Research Institute

Chandna et al. (2021) reported that during pursuit of a target moving on the midline, a covered eye moved out of phase with the viewing eye. However, whether the eyes moved ahead or behind the stimulus was ambiguous since the stimulus moved with a continuous sinusoidal pattern. Here we explicitly evaluate the temporal initiation (latency) of midline pursuit in binocular and monocular conditions in discrete trials in which the target moved towards or away from the observer. Observers pursued a physical accommodative target (circular letters array) that moved in depth on a track aligned with the optical midline (peak vel. = 30cm/s). The stimulus started 50 cm from the observer and then moved towards (50-33 cm) or away (50-67 cm) from them at a random time and direction. After a second random fixation period (1-2 sec), the target then moved in the opposite direction to its initial position. Viewing was binocular, or monocular with one eye obscured with an infrared pass filter. An EyeLink 1000+ measured both eyes’ movements. During monocular viewing, the occluded eye often had a longer latency than the viewing eye, but sometimes anticipated and moved before it, or in other trials remained stationary. Interestingly, even during binocular viewing pursuit initiation in the two eyes was asynchronous, with latencies often differing by 100 msec or more. The data suggest that a single motor command does not drive the eyes during midline pursuit, rather each eye appears to be controlled independently. These results are consistent with a new hybrid model of binocular control with independent eye commands components.

Acknowledgements: NIH 1R01EY034626-01