Multiple object tracking and pupillometry reveal deficits in both selective and intensive attention in unilateral spatial neglect.

Introduction: Unilateral spatial neglect is typically associated with a spatial attention deficit, as neglect patients fail to respond to objects in their contralesional hemispace. However, growing evidence suggests that also nonspatial attention impairments (e.g., arousal) play a role and influences the recovery from this syndrome.Method: Nonspatial and spatial attentional functions were assessed in 13 right-hemisphere stroke patients with neglect, 13 right-hemisphere stroke patients without neglect, and 26 healthy control participants, by investigating pupillary responses and performance on a multiple object tracking task (MOT)that is, a dynamic task of divided attention where cognitive load can be manipulated precisely. The task was alternately presented in the left and right hemispace to assess spatial attention functioning.Results: Results revealed smaller pupillary dilations in both patient groups than in controls, suggesting reduced attentional resources or arousal, and while patients without neglect and controls revealed significant effects of cognitive load on their pupillary responses, neglect patients did not. Both MOT and visual search (VS) tasks revealed spatial symptoms of neglect, while MOT performance measures additionally indicated reduced cognitive functioning in the ipsilateral hemispace. Moreover, the MOT task revealed severely reduced divided attention in neglect patients, as they only managed to track one target in the contralesional hemispace and occasionally two targets at the time in the ipsilesional hemispace.Conclusion: Our results suggest that a stroke may lead to reduced attentional resources. Furthermore, as neglect patients showed no indications in their pupillary responses that they were able to regulate the allocation of resources in accordance with the varying task demands, it appears they additionally had impaired mechanisms for adjusting arousal levels. Our findings suggest that neglect involves nonspatial as well as spatial attention impairments, as also ipsilesional performance was reduced in this group.