Oculomotor challenges in macular degeneration impact motion extrapolation

Macular degeneration (MD), which affects the central visual field including the fovea, has a profound impact on acuity and oculomotor control. We used a motion extrapolation task to investigate the contribution of various factors that potentially impact motion estimation, including the transient disappearance of the target into the scotoma, increased position uncertainty associated with eccentric target positions, and increased oculomotor noise due to the use of a non-foveal locus for fixation and for eye movements. Observers performed a perceptual baseball task where they judged whether the target would intersect or miss a rectangular region (the plate). The target was extinguished before reaching the plate and participants were instructed either to fixate a marker or smoothly track the target before making the judgment. We tested nine eyes of six participants with MD and four control observers with simulated scotomata that matched those of individual participants with MD. Both groups used their habitual oculomotor locus-eccentric preferred retinal locus (PRL) for MD and fovea for controls. In the fixation condition, motion extrapolation was less accurate for controls with simulated scotomata than without, indicating that occlusion by the scotoma impacted the task. In both the fixation and pursuit conditions, MD participants with eccentric preferred retinal loci typically had worse motion extrapolation than controls with a matched artificial scotoma and foveal preferred retinal loci. Statistical analysis revealed occlusion and target eccentricity significantly impacted motion extrapolation in the pursuit condition, indicating that these factors make it challenging to estimate and track the path of a moving target in MD.