Samantha Montoya¹ (), Anna Hillstrom¹, Karly Allison¹, Carter Mulder¹, Mike Lee¹, Michael-Paul Schallmo¹, Stephen Engel¹; ¹University of Minnesota

Visual snow (VS) is the perception of tiny flickering dots covering the visual field. VS is estimated to affect ~4% of the population and, when combined with other symptoms, can be disabling. VS likely arises from spontaneous (non-stimulus driven) activity in the visual pathways, but the specific regions involved are unknown. We sought to determine whether the neural activity producing VS arises at or before motion selective areas. The motion aftereffect (opposite-direction illusory motion perceived after adapting to motion) results from neural adaptation in motion selective regions including area V5/MT. If the activity generating VS reaches these neurons, the VS symptom should be susceptible to the motion aftereffect. Eleven participants with VS viewed high-contrast, horizontally drifting gratings on the left and right of a central fixation point. The gratings (0.3 cyc / degree, 2 Hz) drifted towards or away from the center, which should produce opposing aftereffects. Adapter duration varied across trials (1.6, 5, 15, or 45 sec, each repeated on 4 trials). The gratings were replaced with blank circles in which participants judged the motion of their VS. Participants pressed a button when the motion of the snow inside the circles matched, indicating the duration of the effect. To ensure participants with VS experienced a typical motion aftereffect for external stimuli, stationary square-waves were shown in a control condition. Most participants (10/11) reported that after adaptation, their VS moved in the opposite direction of the adapting gratings. Longer adapter durations resulted in longer-lasting effects (ANOVA F10,1 = 74.4, p = 6.1 ⨉ 10-6) following a power law, consistent with prior motion aftereffect literature. VS was susceptible to the motion aftereffect, indicating the neural activity responsible for snow reaches motion selective neurons, and therefore arises early in the visual pathways, at or before area V5/MT.

Acknowledgements: Supported by a UMN Grant-in-Aid (574483); grants from NEI, NIH (F31 EY034016, T32 EY025187, UL1TR0024940); NINDS (R25 NS117356); and the NSF (DGE 1734815 at the University of Minnesota).