Fixation Preference for Visual and Auditory Targets in Monkeys with Strabismus

Abstract

During binocular viewing, many strabismic subjects choose the eye of fixation depending on the retinotopic location of a visual target. Here, we compare eye choice behavior when orienting to visual and non-visual (auditory) targets. METHODS. Eye movements were measured in two head-fixed exotropic strabismic monkeys in a saccadic task involving either a visual or an auditory stimulus (no visual target information or feedback) during monocular or binocular viewing. The stimulus was one of 21 visual or auditory targets arranged 10°apart in a 7 × 3 array at a distance of 57 cm in an otherwise dark room. Fixation preference was calculated by recording the incidence of using a specific eye to acquire the target at any location. RESULTS. Spatial patterns of fixation preference were observed in both monkeys for both visual and auditory stimuli; targets to the far right were acquired by the right eye, and targets to the far left were acquired by the left eye. For visual targets, the border for a change in fixation preference occurred in between the visual axes of the fixating and deviated eyes (variable in the two animals). In contrast, the border for fixation change remained near the cranio-center during the auditory task. During monocular viewing, fixation switching was observed only at the extremities during visual tasks; during the auditory task, fixation preference was similar to that observed during binocular viewing. CONCLUSIONS. Fixation preference persists for invisible auditory targets. Our data suggest that visual suppression could modify underlying eye choice behavior that functions independently from vision.

A competition framework for fixation-preference in strabismus

“…All procedures were performed per National Institutes of Health guidelines and the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research and the protocols were reviewed and approved by the Institutional Animal Care and Use Committee (IACUC) at the University of Houston. Monkey M1 was used in our previously published study (M1) that examined the behavioral aspect of spatial patterns of fixation preference in strabismic monkeys when presented with auditory vs. visual stimuli ( Ramachandran and Das, 2020 ).…”

“…The goal of this study was to investigate the neural substrate for fixation-preference behavior in strabismus and determine if a competition-framework analogous to target selection in a normally aligned subject could serve as the mechanism that the brain uses to elicit fixation-preference behavior in strabismus. Some of these results have been previously published in abstract form ( Ramachandran and Das, 2022 ).…”

“…This so-called border between right eye and left eye fixation zones is not sharply defined and the monkeys could acquire targets at these locations with either eye ( Agaoglu et al, 2014 ). Interestingly, some recent work, including from our own lab, has shown that fixation-switch behavior can be elicited even in the absence of visual targets suggesting that some aspects are perhaps non-visual ( Economides et al, 2014 , Ramachandran and Das, 2020 ). In the current study, we attempted to investigate the neural basis for fixation-preference by performing neurophysiological recordings in the superior colliculus (SC) of strabismic non-human primates.…”

Visual Stimulus Design for Strabismus in Preverbal Children in Serpong Area as a Prevention of Amblyopia

“…Strabismic subjects with amblyopia (reduced visual acuity) prefer to use their non-amblyopic eye to fixate on the target. [9] Strabismus affects 1% to 3% of children. It is seen more frequently in children with a history of prematurity, systemic diseases, such as cerebral palsy, genetic syndromes, and a family history of strabismus.…”

A Dichoptic Optokinetic Nystagmus Paradigm for Interocular Suppression Quantification in Intermittent Exotropia

“…However, the situation is much more complicated in IXT patients, as their visual suppression condition is unstable and varies with eye position ( Serrano-Pedraza et al, 2011 ; Wakayama et al, 2013 ). Patients with IXT can switch the fixating eye spontaneously according to the object position ( Adams et al, 2017 ; Ramachandran and Das, 2020 ). Thus, suppression can change between eyes depending on fixation.…”