Implicit Processing and Learning of Visual Stimuli in Parietal Extinction and Neglect

Visual extinction and unilateral spatial neglect involve deficits in spatial awareness and attention for stimuli on the side opposite to a brain lesion, typically involving the right parietal cortex. Visual pathways into occipital and temporal cortical areas can be structurally intact. Thus, patients with extinction but no field defect may detect a stimulus presented alone in their contralesional field, but fail to detect the same stimulus when presented with competing stimuli on the ipsilesional side. Several findings suggest that extinguished stimuli can still be unconsciously processed along the structurally spared ventral visual stream, e.g. producing implicit semantic priming effects (e.g. Berti and Rizzolatti, 1992). However, it remains to be established how far such residual processing can proceed in the absence of awareness, and what its consequences are. The ventral stream pathway into temporal cortex is critical not only for object identification but also for long-term memory of visual objects. Here we asked whether residual processing of extinguished stimuli can produce subsequent implicit or explicit memory traces, even when tested many minutes later.