Visual Snow Is Susceptible to the Motion Aftereffect

For people with visual snow, the visual field is covered in faint flickering specks. Visual snow remains poorly understood and lacks effective treatments. The snow is likely produced by spontaneous (non-stimulus driven) activity in the visual system, but the specific neural mechanisms are not known. We hypothesized that the activity producing visual snow is present early in the visual pathways. Here, we tested whether it reaches motion selective areas, including V5/MT, using the motion aftereffect (MAE).

Eleven participants with visual snow syndrome (VSS) and 12 non-snow controls adapted to high contrast drifting gratings on the left and right sides of a central fixation point, moving in opposite directions. After adaptation, participants with VSS viewed their visual snow on a blank screen and pressed a button when the motion visible in the visual snow had no coherent direction. The duration of the adapter gratings varied across trials (1.6-45 seconds). In a control condition, we presented a stationary square wave pattern during the test period to confirm that participants with VSS experienced a typical MAE for external stimuli.

Following adaptation, most participants with visual snow reported that it moved in the opposite direction of the adapting gratings (10/11), as expected for the MAE. Longer adapter durations resulted in longer-lasting illusions and this relationship was linear on a log-log axis, consistent with the MAE literature.

Visual snow is susceptible to the MAE, suggesting that the neural activity producing visual snow reaches motion selective neurons involved in perceiving the MAE, which are believed to include V5/MT. If visual snow arises before area V5/MT, our findings suggest this activity is propagated forward through the visual pathways. Pinpointing the neural origins of visual snow may facilitate the development of novel treatment approaches targeting specific visual brain areas or networks.