Assessment of pseudoneglect using pupillometry

Spatial attention is typically slightly biased leftward (“pseudoneglect”), generally explained by an imbalance in hemispheric activity. Pseudoneglect is mostly assessed with paper-and-pencil tasks, bound to problems such as the need to overtly respond, effects of the hand used for responding, and the inability to track changes over time. We present a pupillometry-based method to assess lateralized attention. Participants viewed alternating black/white and white/black hemifields (Experiment 1; N=15) or bars in the periphery (Experiment 2; N=26) while fixating the center. We assessed whether pupil light responses predominantly reflected the brightness of the left side and correlated differences in pupil responses with traditional measures for pseudoneglect (i.e. greyscales, line bisection). In both experiments, pupil size strongly reflected the left side of the visual display. This is in line with the hemispheric imbalance hypothesis (i.e. peripheral stimuli lead to greater right-hemispheric activation, leading to a leftward bias). Whereas the pupillometry-based attention bias positively related with greyscales performance, this was not seen for line bisection. To conclude, pupil light responses reveal a default lateralized attention bias, without the need of an explicit response. Potentially, this method can be exploited to improve diagnosis of visuospatial neglect following stroke.