Fuseina Safianu¹, Bhagya L Marella¹, Stephanie A Biehn¹, Aishwarya Ravi¹, T Rowan Candy¹; ¹Indiana University

Objective Vergence eye movements are employed to track objects in depth. Change in disparity over time (CDOT) and intraocular velocity differences (IOVD) serve as cues to motion in depth (Giesel et al, 2019). Two studies in our lab have demonstrated vergence responses to (i) disparity alone and (ii) both cues. This study directly assessed the role of CDOT and IOVD in tracking vergence responses of adults. Methods A 10 diameter, spatially 1/f noise texture was presented dichoptically against a mean luminance background at 100cm viewing distance using a PROPixx projector (RB3D mode, VPixx). This stimulus isolates the CDOT cue by dynamically changing both disparity (0.1Hz, 2 amplitude sinusoid) and texture at 120Hz over time. The amplitude of 30s of sinusoidal vergence response was compared to that to a 10 diameter Maltese cross, containing both CDOT and IOVD cues undergoing the same disparity temporal profile (combined cue stimulus). Data were recorded from 10 functionally emmetropic adults using an Eyelink 1000 Plus (SR Research). Results Fast Fourier transforms were performed on the horizontal vergence movements. Group mean vergence amplitude and latency at 0.1Hz for the CDOT stimulus were 1.86(SD:±0.46) and 209ms (SD:±156), and for the combined cue stimulus were 1.93(SD:±0.32) and 152ms (SD:±95), closely matching the amplitude of the sinusoidal stimulus. Increasing the stimulus amplitude to 4° revealed asymmetries between convergence and divergence responses in the CDOT condition for 3 participants while their combined cue responses remained symmetric. The asymmetries were consistent with their phoria and fixation disparity measurements. Conclusion Adults generated robust tracking vergence responses to these textures with naturalistic image statistics. The larger amplitude CDOT stimulus revealed the asymmetric nature of these vergence responses in some adults. Hence, studying infants’ responses to these stimuli holds diagnostic potential for predicting binocular motor function during development.

Acknowledgements: NEI RO1 EY014460