Directional Motion Sensitivity in Visual Snow Syndrome and Its Relation to Trailing-Type Palinopsia.

Purpose: Visual Snow Syndrome (VSS) is characterized by visual perceptual distortions, potentially linked to increased neural excitability and/or decreased inhibition in the visual cortex. If present, these putative physiological abnormalities may alter motion direction sensitivity. Trailing-type palinopsia (TTP), commonly associated with VSS, may further affect motion sensitivity. This study aimed to investigate the sensitivity to direction of motion and its dependence on stimulus size in patients with VSS using the Spatial Suppression paradigm. Methods: We assessed motion duration discrimination thresholds for small (1 degree), medium (2.5 degrees), and large (12 degrees) high-contrast gratings in 23 patients with VSS and 27 healthy control participants. The Spatial Suppression Index (SSI) quantified size-dependent increases in duration thresholds. Visual Discomfort Questionnaire scores and VSS symptom ratings, including TTP, afterimages, photophobia, etc., were also collected. Results: Patients with VSS reported higher visual discomfort and perceptual disturbances, but no group differences were found in duration thresholds or SSI. Notably, higher TTP scores were associated with lower duration thresholds, indicating a facilitatory effect of TTP on sensitivity to direction of motion. Conclusions: Our findings indicate that when VSS is regarded as a unified diagnostic category, it is not associated with impaired motion direction sensitivity or abnormal center-surround suppression. However, our preliminary results suggest that an absence or presence of comorbid TTP has a qualitatively different effect on directional sensitivity in patients with VSS. The facilitatory effect of TTP on motion sensitivity provides insight into the functional concomitants of TTP, and warrants further exploration, as it may significantly influence experimental outcomes.