Abstract
Introduction: In the Ebbinghaus illusion, a shape appears larger than its actual size when surrounded by small shapes and smaller than its actual size when surrounded by large shapes. Resistance to this visual illusion has been previously reported in schizophrenia, and linked to disorganized symptoms and poorer prognosis in cross-sectional studies. It is unclear, however, when in the course of illness this resistance first emerges or how it varies longitudinally with illness phase.Method: We addressed these issues by having first-episode psychosis patients, multiple-episode schizophrenia patients and healthy controls complete a psychophysical task at two different time points, corresponding to hospital admission and discharge for patients. The task required judging the relative size of two circular targets centered on either side of the screen. Targets were presented without context (baseline), or were surrounded by shapes that made the size judgment harder or easier (misleading and helpful contexts, respectively). Context sensitivity was operationalized as the amount of improvement relative to baseline in the helpful condition minus the amount of decrement relative to baseline in the misleading condition.Results: At hospital admission, context sensitivity was lower in the multiple-episode group than in the other groups, and was marginally less in the first episode than in the control group. In addition, schizophrenia patients were significantly more and less accurate than the other groups in the misleading and helpful conditions, respectively. At discharge, all groups exhibited similar context sensitivity. In general, poorer context sensitivity was related to higher levels of disorganized symptoms, and lower level of depression, excitement, and positive symptoms.Discussion: Resistance to the Ebbinghaus illusion, as a characteristic of the acute phase of illness in schizophrenia, increases in magnitude after the first episode of psychosis. This suggests that visual context processing is a state-marker in schizophrenia and a biomarker of relapse and recovery.
Highlights
In the Ebbinghaus illusion, a shape appears larger than its actual size when surrounded by small shapes and smaller than its actual size when surrounded by large shapes
Ebbinghaus illusion, clinical state, schizophrenia related to problems in daily functioning in schizophrenia (Green et al, 2012); and (7) some visual abnormalities in schizophrenia are related to clinical state (Silverstein et al, 1996; Uhlhaas et al, 2005; Keane et al, 2013), suggesting they may be biomarkers of relapse, recovery, or treatment response, whereas other abnormalities are stable over time and can be found in unaffected relatives, suggesting they may be genetic or endophenotype markers (Yeap et al, 2006)
This paper is the first report from an ongoing longitudinal study that investigates whether perceptual measures can predict symptom severity and/or level of functioning across multiple time points. This is only the second study to examine longitudinal and treatment-related change in visual perception in schizophrenia and it is the first study of any kind to examine surround suppression in persons with a first episode of psychosis
Summary
In the Ebbinghaus illusion, a shape appears larger than its actual size when surrounded by small shapes and smaller than its actual size when surrounded by large shapes. We chose this illusion because it has been established over decades of research, because it is experienced to a lesser extent among schizophrenia patients relative to healthy and psychiatric controls (Uhlhaas et al, 2006a,b; Tibber et al, 2013), and because reduced illusions have been linked to a more acutely ill clinical state and to more disorganized symptoms in crosssectional studies (Uhlhaas et al, 2006a,b; Horton and Silverstein, 2011) Another advantage to this task is that it can side-step generalized deficit confounds, in which low accuracy can be attributed to reduced motivation or attention (Knight and Silverstein, 2001; Silverstein, 2008). In the Ebbinghaus task, patients are expected to perform better than healthy controls in the misleading context condition, worse than controls in the helpful context condition, and about the same in the no-context condition
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