Does pupillometry provide a valid measure of spatial attentional bias (pseudoneglect)?

Strauch et al. (2022) introduced a novel approach to assess biases of visual attention, by measuring pupillary constriction in response to split-field stimuli, in which a bright patch is presented to one visual field and a dark patch to the other. Their study suggested that pupillary constriction is more pronounced in response to bright stimuli in the left visual field compared to the right, consistent with a neurotypical attentional bias towards the left side (pseudoneglect). This pupillometric bias was also found to correlate with performance on the greyscales task, an established behavioural measure of pseudoneglect. The present study sought to replicate these findings, and investigated the influence of the eye of recording on the pupillary constriction bias measured by this split-field method (n = 80). There was a major influence of the eye of recording, whereby each pupil constricted more to light in the ipsilateral than the contralateral visual field (d = 1.67). Averaging across the eyes, we confirmed stronger pupillary constriction to bright stimuli in the left compared to the right visual field (pseudoneglect), but with a small effect size (d = -.31). While the split-field paradigm does detect pseudoneglect, it does not seem to be especially sensitive, and large sample sizes may be required to detect this subtle bias. However, the method may hold promise for studying stronger attentional biases, such as those seen in spatial neglect.