Characteristics of free visual exploration patterns in subjects at ultra-high risk for psychosis

Abstract

Objective To investigate the eye-movement feature of free visual exploration in medication-naive subjects at ultra-high risk for psychosis. Methods Eye movements of 50 subjects at ultra-high risk for psychosis and 40 healthy controls evaluated by the Structured Interview for Prodromal Syndromes were recorded using EyeLink desktop eye tracking system. Healthy controls were matched with subjects at ultra-high risk for psychosis in gender, age and education level. The differences in fixation count, total time, fixation duration, saccadic count, saccadic amplitude and scanpath length as well as changes of these indices over the exploration course were analyzed. Results Subjects at ultra-high risk for psychosis statistically showed fewer fixation count (24±1 vs. 26±1, t=-2.314, P=0.023), fewer saccadic count (23±4 vs. 25±3, t=2.322, P=0.023), shorter scanpath length ((113±29)° vs. (130±28)°, t=2.772, P=0.007) and longer fixation duration ((362±85) ms vs. (321±52) ms, t=-2.866, P=0.005) compared to healthy controls. There were no statistical differences in total time and saccadic amplitude. A significant interaction of group×time(Fgroup×time (3, 86)= 3.115, P=0.030) in saccadic amplitude was found when testing changes in fixation duration and saccadic amplitude over the exploration time course. Conclusions Subjects at ultra-high risk for psychosis showed a limited scanpath pattern of visual exploration comparing with healthy controls. The pathophysiological significance of eye-movement abnormality in subjects at ultra-high risk deserves further research. Key words: Schizophrenia; Eye movements; Ultra-high risk for psychosis; Free visual exploration