Idiopathic infantile nystagmus syndrome is a disorder characterised by involuntary eye movements, which leads to decreased acuity and visual function. One such function is visual crowding; a process whereby objects that are easily recognised in isolation become impaired by nearby flankers. Crowding typically occurs in the peripheral visual field, though elevations in foveal vision have been reported in congenital nystagmus, similar to those found with amblyopia. Here we examine whether the elevated foveal crowding with nystagmus is driven by similar mechanisms to those documented in amblyopia - long-term neural changes associated with a sensory deficit - or by the momentary displacement of the stimulus through nystagmus eye movements. We used a Landolt-C orientation identification task to measure threshold gap sizes with and without either horizontally or vertically placed pairs of flanking Landolt-Cs. Because nystagmus is predominantly horizontal, crowding should be stronger with horizontal flankers if eye movements cause the interference, whereas a sensory deficit would more likely be equivalent for the two dimensions. Consistent with an origin in eye movements, we observe elevations in nystagmic crowding that are above that of typical vision, and stronger with horizontal than vertical flankers and not found in amblyopic or typical vision. We further demonstrate the same pattern of performance can be obtained in typical vision with stimulus movement that simulates nystagmus. Consequently, we propose that the origin of nystagmic crowding lies in the eye movements, either through image smear of the target and flanker elements or through relocation of the stimulus into peripheral retina.

中文翻译：

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眼球运动增加特发性婴儿眼球震颤综合征的拥挤度

特发性婴儿眼球震颤综合征是一种以眼球不自主运动为特征的疾病，可导致视力和视觉功能下降。其中一项功能是视觉拥挤；一个很容易被孤立识别的物体被附近的侧翼破坏的过程。拥挤通常发生在周边视野中，尽管在先天性眼球震颤中报道了中央凹视力升高，类似于弱视。在这里，我们检查升高的中心凹拥挤与眼球震颤是否是由与弱视中记录的类似机制驱动的 - 与感觉缺陷相关的长期神经变化 - 或通过眼球震颤眼球运动的刺激的瞬时位移。我们使用 Landolt-C 方向识别任务来测量有和没有水平或垂直放置的侧翼 Landolt-C 对的阈值间隙大小。因为眼球震颤主要是水平的，如果眼球运动引起干扰，水平侧翼的拥挤应该更强，而感觉缺陷更可能在两个维度上是等效的。与眼球运动的起源一致，我们观察到眼球震颤拥挤的升高高于典型视力，并且水平侧翼比垂直侧翼更强，并且在弱视或典型视力中没有发现。我们进一步证明了在典型视觉中可以通过模拟眼球震颤的刺激运动获得相同的表现模式。因此，我们提出眼球震颤拥挤的起源在于眼球运动，