Asymmetric Adaptation of Catch-up Saccades with Artificial Central Scotomas

In fully-sighted individuals, pursuit and saccadic eye movements work together to foveate moving targets; pursuit attempts to match target velocity, while catch-up saccades re-align the fovea to the target if it deviates during pursuit. Although saccade-pursuit interactions are well understood in healthy individuals, much less is known about how these mechanisms adapt in the presence of central vision loss. Here, we simulated central vision loss in healthy young adults to examine plasticity in saccade-pursuit mechanisms and investigated whether and how catch-up saccades adapted over five days of visual tracking. Twenty-five fully sighted participants performed a task in which they pursued a moving target that stepped position randomly (designed to elicit catch-up saccades) while viewing with a gaze-contingent central scotoma. The scotoma was shaped like a bitten cookie to encourage use of a specific preferred retinal locus (PRL) corresponding to the peripheral location with the highest acuity. By the end of the five days of repetition, most participants showed catch-up saccade endpoints shifted towards the PRL rather than the fovea. On average, endpoints shifted 0.5 deg towards the PRL between days 1 and 5 (range=0.3-1.5 deg), with significant shifts in 13 of the 25 participants. Adaptation was asymmetric; shifts were largest when the target moved in the direction opposite the scotoma bite and smallest when it moved towards it. In summary, we observed adaptation of saccade-pursuit interactive mechanisms through the re-referencing of catch-up saccades from the fovea to PRL. These results provide a promising avenue for rehabilitation in central vision loss aimed at improving eye movements and encouraging PRL use. Ultimately, such an approach may enhance residual visual function and quality of life.