Because the visual system cannot process all of the objects, colors, and features present in a visual scene, visual attention allows some visual stimuli to be selected and processed over others. Most research on visual attention has focused on spatial or location-based attention, in which the locations occupied by stimuli are selected for further processing. Recent research, however, has demonstrated the importance of objects in organizing (or segregating) visual scenes and guiding attentional selection. Because of the long history of spatial (...) attention research, theories of spatial attention are more mature than theories of other visual processes, such as object segregation and object attention. In the present paper, I outline a biased competition account of object segregation and attention, following similar accounts that have been developed for spatial attention (Desimone and Duncan, 1995). In my biased competition account, I seek to understand how some objects can be segregated and selected over other objects in a complex visual scene. Under this account, there are two sources of visual information that allow an object to be processed over other objects: bottom-up information carried by the physical stimulus and top-down information based on an observer's goals. I use the biased competition account to combine many diverse findings from the object segregation and attention literatures into a common framework. (shrink)

Neuropsychological deficits have been widely used to elucidate normal cognitive functioning. Can patients with such deficits also be used to understand conscious visual experience? In this paper, we ask what it would be like to be a patient with apperceptive agnosia . Philosophical analyses of such questions have suggested that subjectively experiencing what another person experiences would be impossible. Although such roadblocks into the conscious experience of others exist, the experimental study of both patients and neurologically normal subjects can be (...) used to understand visual processing mechanisms. In order to understand the visual processes damaged in apperceptive agnosia, we first review this syndrome and present a case study of one such patient, patient J.W. We then review several theoretical accounts of apperceptive agnosia, and we conclude that studies of the patients themselves may not allow us to discriminate between the various explanations of the syndrome. To test these accounts, we have simulated apperceptive agnosia in neurologically normal subjects. The implications of our results for understanding both apperceptive agnosia and normal visual processing are discussed. (shrink)