Anomalous temporal integration and segregation in visual snow syndrome

Abstract

Purpose : Visual snow syndrome (VSS) is a neurological condition named after a visual disturbance consisting of tiny, dynamic dots. However, diagnosis requires additional symptoms such as palinopsia (afterimages and/or trailing). In an observational, cross-sectional study, we tested the hypothesis that those with VSS have an increased tendency to integrate rather than segregate successive visual stimuli.

Methods : We tested temporal integration and segregation ability in 20 controls (aged 19 - 42, mean 27.6 years) and 26 people with VSS (aged 19 - 39, mean 28.5 years). Complimentary parts (Figure 1A) of a 4 x 4 grid of elements (0.5° element width and separation) were presented for 12ms each separated by a variable blank interstimulus interval (ISI). The grid contained a missing element that was identifiable if successive images were integrated and an odd element that appeared as two successive half circles if the images were segregated. In separate blocks, participants located the missing or odd element in a method of constant stimuli. Nine ISIs were tested (12, 24, 35, 47, 59, 71, 82, 94, 106ms) with 20 repeats each. Logistic psychometric functions were fit to individual data for each task to extract 50% correct thresholds, which were analysed using a repeated measures ANOVA with task and group as factors.

Results : There was a significant interaction between group and task (F(1,44)=12.96, p<0.001, η_p²=0.23, Figure 1B), with threshold ISIs that were longer in those with VSS compared to controls for the missing-element task (F(1,44)=4.97, p=0.031, η_p²=0.10, mean difference and 95% CI 12.85 [1.24 - 24.47]), indicating integration at longer ISIs. However, threshold ISIs were shorter for the odd-element task in VSS (F(1,44)=7.77, p=0.008, η_p²=0.15, mean difference and 95% CI -7.31 [-12.60 - -2.02]), signifying segregation at shorter ISIs. Individuals with prolonged integration did not exhibit poor segregation, as task thresholds were not correlated (controls: r=0.38, p=0.098; VSS: r=0.19, p=0.35).

Conclusions : Our results indicate measurable differences in temporal processing in VSS. The VSS group either continued to integrate despite longer gaps between successive stimuli, or if the task required, segregate stimuli that were in close succession. Prolonged temporal integration in VSS may relate to symptoms of palinopsia.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Figure 1A) Task procedure B) Mean thresholds and 95% CI for each group