A new oculomotor model demystifies "Remarkable Saccades"

Abstract

Herings Law of binocular eye movement control guides most oculomotor research and supports diagnosis and treatment of clinical eye misalignment (strabismus). The law states that all eye movements are controlled by a unitary conjugate signal and a unitary vergence signal that sum. Recent evidence of temporally asynchronous inter-eye rotations during vergence (Chandna et al., 2021) challenges the viability of a unitary vergence signal. An alternative theory that might explain these anomalous results posits that the eyes are controlled independently. Yet independent control fails to explain a phenomenon known as "Remarkable Saccades" where an inappropriate saccade occurs from an eye aligned on a target during asymmetric vergence (Enright, 1992). We introduce a new model formulated to describe the Chandna et al. (2021) midline vergence result that generates remarkable saccades as an emergent property. The Hybrid Binocular Control model incorporates independent controllers for each eye with a cortical origin that interact with a unitary conjugate controller residing in brainstem. The model also accounts for behavioral variations in remarkable saccades when observers attend to an eye. Furthermore, it suggests more generally how the eyes are controlled during vergence and other voluntary eye movements, thus challenging documented oculomotor neural circuitry and suggesting that refinements are needed for clinical oculomotor interventions.