Fine-scale eye-movement differences in psychosis and their contribution to abnormal vision

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Project summary/abstract Eye movement abnormalities in schizophrenia (SZ) have been documented for over 100 years, yet it remains unknown whether fine-scale eye movements differ in this population. This is unfortunate because the neural structures underlying oculomotor control are well-documented, implying that group differences could shed light on the underlying illness pathophysiology. Moreover, establishing fine-scale eye movement differences could in principle provide a distinguishing biobehavioral marker, which in turn could be used for differential diagnosis or clinical prediction. Additionally, fine-scale eye movements contribute to everyday activities, such as recognizing facial expressions at a distance, reading, and discriminating fine spatial stimuli. Therefore, it is conceivable that abnormal micro- eye movements could be associated with—and even causally related to—impairments of these visual functions in psychosis. Thus, a major goal of the research described in this proposal is to establish that fine-scale eye movements do indeed differ among those with psychosis (Aim 1). These differences will be assessed in people with a psychotic disorder and in well-matched healthy adults during steady fixation and in the presence of complex foveal stimuli. In contrast to possibly all prior psychosis studies, we will use a high- precision digital Dual Purkinje Image Eye-Tracker (1 arcmin resolution) with a head-stabilizing helmet to minimize small head motions, and frequent re-calibrations throughout data collection. Additionally, a custom-made system for gaze contingent display control, will enable the implementation of a state-of-the-art calibration procedure, which effectively reduces the gaze localization error to less than 5 arcmin. Since visual acuity and reading are often impaired among psychosis patients and may even portend a future psychotic disorder, we will attempt to generate group differences with tasks that probe these same processes. Moreover, to establish a reference baseline for fine oculomotor behavior and to consider hitherto unnoticed problems in fixational stability, we will assess small eye movement differences during steady fixation without an active task. Aside from assessing whether micro- eye movement differences characterize psychosis, we will also assess their relationship to visual perceptual deficits (Aim 2). In particular, we will probe for correlations between microsaccade characteristics and the magnitude of visual acuity and reading deficits. We will also consider whether trials with a higher rate of microsaccades are related to impaired reading or impaired visual acuity compared to trials without such eye movements, and whether image stabilization on the retina (which removes the benefits of microsaccades) worsens acuity more for controls than for patients. Findings will inform our understanding of how eye movement differences in psychosis are related to perception at the micro-scale, which in turn can suggest novel treatments or interventions for improving poor visual acuity and reading.