PREATTENTIVE FILLING-IN OF VISUAL SURFACES IN PARIETAL EXTINCTION

Unilateral brain damage frequently produces ''extinction,'' in which p atients can detect brief single visual stimuli on either side but are unaware of a contralesional stimulus if presented concurrently with an ipsilesional stimulus. Explanations for extinction have invoked defic its in initial processes that operate before the focusing of visual at tention or in later attentive stages of vision, Preattentive vision wa s preserved in a parietally damaged patient, whose extinction was less severe when bilateral stimuli formed a common surface, even if this r equired visual filling-in to yield illusory Kanizsa figures or complet ion of partially occluded figures. These results show that parietal ex tinction arises only after substantial processing has generated visual surfaces, supporting recent claims that visual attention is surface-b ased.