"Both" means more than "two": localizing and counting in patients with visuospatial neglect

We report that in patients with hemispatial neglect after parietal damage, visual awareness critically depends on different attentional demands for enumeration or localization. Neglect patients usually fail to attend to stimuli in the hemifield contralateral to the lesion (contralesional) and 'extinguish' them when simultaneously presented with competing stimuli ipsilateral to the lesion (ipsilesional), even though primary visual pathways are intact, and a contralesional stimulus presented alone is detected. Here we show that contralesional extinction differed when patients enumerated or located stimuli in space. Enumerating only a few (≤ 4) visual elements may exploit 'subitizing' mechanisms independent from spatial attention (unlike 'counting' of more elements), as is the case in normal people.