Task-sensitivity of unconscious word processing in spatial neglect.

Abstract Neuropsychological studies of spatial neglect have shown that ignored visual stimuli can produce measurable behavioral changes without eliciting subjective perceptual experience. However, such non-conscious, implicit cognitive processing may not be fully automatic but rather could be influenced by the patients’ voluntary behavioral control. Using a hemifield priming paradigm with two different task instructions, we studied spatial neglect patients to assess whether non-conscious processing of ignored words is modulated by behavioral task requirements. In each trial, participants named or categorized a centrally presented target following a masked prime flashed to the left or right hemifield. By delivering equally invisible stimuli to both hemifields, this design allowed rigorous testing of the impact of task instructions on non-conscious processing in neglect patients and control participants. We observed that neglect patients showed slightly different patterns of masked priming from those obtained in healthy and right-hemisphere control patients. Importantly, however, all these three groups showed strong sensitivity to task contexts during the unconscious processing of masked words. The present results provide neuropsychological evidence that robust task-sensitive neural pathways are covertly operating on weak and normally imperceptible visual stimuli even when visuospatial attention is severely compromised.