Visual snow is affected by contrast adaptation

Visual Snow Syndrome (VSS)—a condition defined by the continuous perception of flickering dots/specks covering the visual field—affects about 2% of the population and its symptoms can interfere with tasks like reading and driving. However, little is known about the mechanisms underlying VSS, and effective treatments are lacking. Adaptation, in which viewing an initial stimulus results in altered perception of a subsequent stimulus, is a useful psychophysical tool for exploring visual mechanisms. One hallmark of adaptation is that longer adapting periods produce longer-lasting effects. Here, we tested whether adaptation could alter the appearance of visual snow and whether the effects followed this typical dependence on adapting duration. Participants with VSS (n=17) fixated at the center of the screen while viewing a high-contrast, achromatic noise adapting pattern (10° visual angle at 6° eccentricity, 60Hz, pixel luminances drawn from a random uniform distribution) presented to the left or right of fixation. Participants adapted for 1.6, 5, 15, or 45 seconds (randomly ordered), after which the adapter was replaced by a gray square, outlined in black, matching the background. Participants then pressed a button to indicate when their visual snow within the adapted square matched the intensity of their snow in an identical square on the unadapted side. This recovery time increased with adapter duration (3-way ANOVA testing linear effect of duration, F=18.41, p=0.0006), from an average of 2.2s for the 1.6s adapter to 9.6s for the 45s adapter. Participants also reported how the adapter affected their visual snow. The visual snow disappeared for 50% of participants, weakened for 6%, strengthened for 17%, and remained about the same for 27%. Adaptation can affect visual snow, and may be a promising method for developing novel diagnostic tests and treatments for VSS.