Visual crowding in infantile idiopathic nystagmus is not reduced by differences in target-flanker elements

Abstract

Foveal vision in individuals with infantile idiopathic nystagmus syndrome (IINS) is impaired by reduced acuity and elevated crowding (the disruption in object recognition from clutter). In typical peripheral vision, acuity can be improved by temporal variations (flicker), while crowding is reduced when the target differs in appearance from surrounding flankers. We examined whether flicker and target-flanker differences in contrast polarity could similarly improve foveal performance in IINS and typical participants (n = 6 each, aged 24-50), who identified the orientation of a foveal Landolt-C presented alone or with 4 black (same polarity) or white (opposite polarity) flankers. Elements were either static or flickered with periodic contrast-polarity reversals. To simulate IINS, typical participants also viewed stimuli with motion derived from nystagmus eye movements. QUEST was used to scale elements to find the threshold gap size. We observed clear foveal crowding effects in both typical and IINS groups, with higher thresholds when flanked than unflanked. Thresholds were elevated in all conditions for the IINS group. Unlike peripheral vision, thresholds with same-polarity flankers did not differ from those with opposite-polarity flankers in either group. Similarly, flicker did not reliably improve performance over static presentation. These patterns differed in simulated nystagmus, which produced elevated crowding levels that were reduced by both target-flanker polarity differences and flicker. Overall, we show that target-flanker differences and flicker do not reduce foveal crowding in IINS. This pattern is unlike both peripheral vision and simulated nystagmus, suggesting that nystagmus disrupts vision through both momentary eye-movement effects and a longer-term sensory deficit.