Eye movement patterns during free visual exploration in schizophrenia: scanpath organization and group differences

Eye movements represent an objective and quantitative indicator of the integrity of cognitive and perceptual processes. Since the beginning of the 20th century, research has consistently shown that individuals with schizophrenia demonstrate characteristic deviations in smooth pursuit, saccadic regulation, and, in recent decades with advances in non-invasive methods, also shown that there are deviations in visual exploration behaviour. Since structured tasks limit behaviour, free visual exploration paradigms allow the assessment of spontaneous gaze behaviour under ecologically valid conditions. Modern research with free-viewing eye-movement paradigms includes quantitative analysis of the number and duration of fixations, scan length, degree of coverage, spatial dispersion and gaze entropy. In one of the landmark studies, Benson et al. (2012) demonstrated that simple metrics from free-viewing tests – such as fixation distribution and scan dynamics – can distinguish patients with schizophrenia with high accuracy from healthy controls, including in independent samples (Beedie, Benson & St. Clair, 2011). In patients with schizophrenia, lower entropy and reduced spatial variance were consistently found, reflecting more stereotyped and less adaptive strategies of visual exploration. These findings have been systematically reviewed by Beedie, Benson & St. Clair (2011) and these oculomotor alterations have been linked to dysfunctions in attention, executive control, and perceptual organisation, and in the last decades they are increasingly discussed as potential biomarkers of impaired neural network regulation. The aim of this ongoing study is to examine group differences in free visual exploration between patients with schizophrenia, healthy controls, and first-degree relatives, and to explore scanpath organization using complementary analytical approaches. Eye movements were recorded during passive viewing of abstract and landscape images in three groups: patients (n = 30), controls (n = 30), and close relatives (n = 21). Visual exploration was assessed using multiple eye-tracking measures, including; fixation count, fixation duration (mean, median, and total), scanpath length, coverage fraction, spatial dispersion (mean and median dispersion, dispersion_x, dispersion_y); center bias, fixation rate, gaze entropy (bits), and saccade metrics. In addition, group-level scanpaths were derived using Dynamic Time Warping Barycenter Averaging (DBA) to identify the clustered patterns in gaze trajectories. Preliminary results indicate consistent group differences in visual exploration. Patients with schizophrenia show reduced scanpath length, lower coverage of the visual field, and more centrally located gaze patterns compared to healthy controls. These alterations were observed across both abstract and landscape images, suggesting a stimulus-independent effect. First-degree relatives showed intermediate patterns, with less pronounced deviations. DBA analysis further illustrated these differences at the level of scanpath organization. Controls demonstrated broader and more spatially distributed exploration, including peripheral regions of the stimuli, whereas patients exhibited more compact and restricted scanpaths, with limited exploration of upper and lateral areas, focusing central area of the stimuli. These findings suggest that free visual exploration captures a restricted and less flexible mode of visual behaviour in schizophrenia. The convergence of quantitative measures and scanpath-based analysis supports the presence of altered cognitive–perceptual regulation. Ongoing analyses will further quantify these effects and examine their clinical relevance.

References

Benson PJ, Beedie SA, Shephard E, Giegling I, Rujescu D, St Clair D. Simple viewing tests can detect eye movement abnormalities that distinguish schizophrenia cases from controls with exceptional accuracy. Biol Psychiatry. 2012 Nov 1;72(9):716-24. doi: 10.1016/j.biopsych.2012.04.019. Epub 2012 May 22. PMID: 22621999. Beedie SA, Benson PJ, St Clair DM. Atypical scanpaths in schizophrenia: evidence of a trait- or state-dependent phenomenon? J Psychiatry Neurosci. 2011 May;36(3):150-64. doi: 10.1503/jpn.090169. PMID: 21223647; PMCID: PMC3080511.