The orienting response might define pseudoneglect. Evidence from a novel pupillometric method.

Spatial attention is generally slightly biased leftward (“pseudoneglect”), a phenomenon 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. I here describe how we objectively assessed lateralized attention over time, exploiting the phenomenon that changes in the pupil reflect the allocation of attention in space. Pupil sizes of 41 healthy participants fixating the center were predominantly influenced by the differential background luminance of the left side of the visual display and driven by visual information in the periphery. Differences in pupil sizes positively related with greyscales scores, but not line-bisection. Time-based analyses within trials show strongest effects early on. With increasing trial number, the initial leftward bias shifted central in pupillometry-based and greyscales measures. This suggests that the orienting response determines the size and direction of pseudoneglect, an account which might explain previously thought opposing findings.
As an outlook, I will show some preliminary findings on patients with clinical hemispatial neglect, discussing the viability of the here described methods for neuropsychological assessment/diagnosis.