A new oculomotor model demystifies "Remarkable Saccades"

Hering's Law of binocular eye movement control guides most oculomotor research and supports diagnosis and treatment of clinical eye misalignment (strabismus). It states that all eye movements are controlled by a unitary conjugate signal and a unitary vergence signal that sum. Recent evidence of temporally asynchronous eye rotations during vergence (Chandna et al., 2021) challenges the viability of a unitary vergence signal. Helmholtz proposed an explanation of binocular control that does not require a vergence system, that the eyes are controlled independently. Yet independent control fails to explain "Remarkable Saccades", inappropriate saccades that occur from an eye aligned on a target during asymmetric vergence (Enright, 1992). Here we present a novel computational architecture of binocular eye movement control based on a concept proposed in Chandna et al. (2021). Our "Hybrid Binocular Control" (HBC) model incorporates simplified pursuit and saccadic components. The pursuit component is implemented with independent controllers for each eye that interact with the saccade component, a unitary conjugate controller. The model generates remarkable saccades as an emergent property, and a variable attentional gain allows it to generate behavioral variations in remarkable saccades that occur when observers attend to one eye's view. In its current form, the model's output matches not only the remarkable saccade profiles well, but other saccade types. However, it does not attempt to specify their exact dynamics or underlying circuitry. The model's novel architecture operates without a vergence signal and makes predictions about how conjugate and independent controller signals interact. Furthermore, it suggests exciting exploration of neural oculomotor circuitry and inspires systematic investigations of asymmetric eye movements and their resulting main sequences necessary for further model elaboration.