Pupillometry as index for biases in spatial attention: pseudoneglect in healthy controls, useful tool for diagnosing cerebral visual impairments?

Spatial attention is generally slightly biased leftward (“pseudoneglect”). This phenomenon is typically assessed with paper-and-pencil tasks, limited by the requirement of explicit responses and the inability to assess on a sub-second timescale. Furthermore, pseudoneglect is often stable within experiments, but differs vastly between investigations and is sometimes expressed to the left, sometimes to the right. We present a pupillometry-based method to assess spatial attention in an objective manner. The method is based on the principle that changes in pupil size associated with changes in light level are not purely reflexive, but are modulated by spatial attention. More specifically, the pupil changes size as covert attention is moved to parts of the visual scene of differing brightness. Healthy participants (N=41) viewed alternating black/white or white/black stimuli while fixating the center. Pupil sizes were more influenced by bright and peripheral stimuli presented on the left side as compared with the right side of the visual display. In ongoing work, we assessed the feasibility of this method for the diagnosis of visuospatial neglect, a frequent condition after right hemispheric brain damage in which attention to the left side of space is reduced. Indeed, neglect patients (N=3) showed stronger pupil light responses to the right side than the left side of the display, whereas age-matched healthy controls (N=12) did not show this pattern. Furthermore, patients with hemianopia or quadrantanopia (N=7), a visual impairment caused by brain damage in the occipital lobe, showed a similar pattern, where the pupil light responses were stronger for the side of the intact rather than defect visual field. This method could be exploited to improve diagnosis of visuospatial neglect following stroke. Objective assessment of neglect is relevant not only for clinical diagnosis (i.e. to provide psycho-education and to select appropriate treatment), but also for outcome measurement in clinical trials.