External Dynamic Visual Noise Matched to the Appearance of Visual Snow Fails to Reproduce Key Perceptual Properties of the Phenomenon.

PURPOSE: Patients with visual snow (VS) perceive a disturbance resembling analog television noise while basic visual measures such as visual acuity remain unaffected. This study investigated whether external dynamic visual noise perceptually matched to VS (simulated VS) reproduces the motion percept of VS during smooth pursuit and whether the subjective awareness of low-contrast simulated VS differed between the VS participants and controls. METHODS: We compared 35 VS participants with 30 healthy controls. Participants adjusted the size, density, flicker rate, and luminance polarity of a high-contrast noise stimulus to match their VS. We measured contrast-detection thresholds and the proportion of near-threshold simulated VS stimuli that were reported as perceived. The perceived motion VS was compared with simulated VS during pursuit. Simulated VS either moved with the pursuit target or remained stationary on the screen. RESULTS: Stimuli matching VS consisted of small (2.2 arcmin), sparse (density 0.06), rapidly flickering (15 Hz) elements both lighter and darker than the background. Contrast-detection thresholds did not differ between groups; however, participants with VS reported perceiving low-contrast stimuli less frequently than controls. During pursuit, participants judged the motion of their own VS as more similar to the stationary than to the moving simulation. CONCLUSIONS: VS does not necessarily affect basic contrast sensitivity but can influence perceptual awareness of low-contrast stimuli. In addition, the motion percept of VS during smooth pursuit cannot be fully reproduced by perceptually matched external noise, suggesting differences in how extraretinal eye-movement signals interact with the neural activity underlying VS and external dynamic noise.