The dichoptic flash-lag effect in controls and amblyopes

Abstract

Purpose : Neural processing of sensory input in the brain takes time, due to the time taken for neural transmission and sensory integration. This creates a potential challenge for the visual system to accurately localize moving objects. One way the brain might overcome this is through motion extrapolation: using the past trajectory of a moving object to predict its future position. In this study we wanted to investigate (i) whether such extrapolation mechanism operate between the eyes in normally sighted observers; and (ii) whether extrapolation processes could be defective in the amblyopes as these patients exhibit an interocular processing delay.

Methods : To measure interocular extrapolation we used a dichoptic flash-lag effect (FLE) paradigm. Twelve adults amblyopes and 12 control subjects participated in the experiment. We measured the FLE magnitude of the subjects under binocular, monocular and dichoptic conditions.

Results : In controls, the FLE magnitude of binocular viewing was significantly smaller than that of monocular and dichoptic viewings (P ≤ 0.023), but there was no difference between monocular and dichoptic conditions. Amblyopes exhibited a smaller FLE magnitude in the dichoptic condition when the moving bar was presented to the amblyopic eye and the flash to the dominant eye (DA condition) compared to the opposite way around (DF condition), consistent with a delay in the processing of the amblyopic eye (P = 0.041).

Conclusions : Our observations confirm that trajectory extrapolation mechanisms transfer between the eyes of normal observers. However, such transfer may be impaired in amblyopia. The smaller FLE magnitude in DA compared to DF in amblyopes could be due to an interocular delay in the amblyopic visual system. The observation that normal controls present a smaller FLE in binocular conditions raises the question whether a larger FLE is or is not an indicator of better motion processing and extrapolation.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.