Fixation Task: A Simple Eye Movement Task Reveals an Impairment in Schizophrenia

Fixation stability (FS) is a basic substrate of visuomotor processing that can be assessed by tracking eye movements during a simple, easy-to-perform task of gazing at a visual stimulus. We studied FS with and without distractors for its potential as an endophenotype marker in antipsychotic-naïve/free schizophrenia (SCZ), SCZ first-degree relatives (FDRs), and healthy controls (HC).

Monocular high-frequency eye tracking data were recorded during a fixation stability task in 69 antipsychotic-naïve/free SCZ, 49 FDRs, and 76 HCs. The task required maintenance of gaze on a central circular target while ignoring an identical peripheral distractor, when present, at near/farther distances on either side. Fixation stability across the groups and the effect of laterality and distance of the distractor effect were analyzed using ANCOVA and RMANCOVA.

SCZ had significantly higher fixation frequency, saccade amplitude, and scanpath length compared to the other groups, even in trials without distractors (ηp2 = 0.05-0.07). Introducing distractors resulted in further worsening of performance in SCZ (ηp2 = 0.09-0.23). First-degree relatives showed impairment in median fixation duration (ηp2 = 0.13). Higher saccade amplitudes and scanpath lengths (both ηp2 = 0.09) were noted in trials with farther distractors across the groups. A significant interaction effect of the laterality * group was noted on scanpath length (ηp2 = 0.03).

FS impairment was noted in antipsychotic naïve/free SCZ, and it worsened with the introduction of distractors. An inversed laterality effect (rightward-bias) of distractor was noted in SCZ and their FDRs, suggesting a possible association of attenuation/reversal of visual functional asymmetry with SCZ vulnerability. Future studies should evaluate FS as illness markers across different clinical stages.