Object-based neglect: an investigation of the contributions of eye movements and perceptual completion

Eye movements made by a patient with object-based neglect and no hemianopia, R.R., were recorded while he viewed whole, half, and chimaeric objects. When whole or chimaeric objects were presented centred on his initial fixation point, and when right half objects were presented, R.R. restricted his saccades to the right sides of the images. R.R.'s verbal identifications were consistent with these scan paths, since he correctly reported the identities of whole objects, right half objects, and the right sides of chimaeric objects, but failed to report objects on the left sides of chimaerics. When a left half object was presented to the left of initial fixation, however, R.R. made left saccades to scan the image and correctly named these objects; hence his failure to scan the left sides of chimaeric object cannot simply be attributed to an inability to make contralesional saccades. We examined the possibility of perceptual completion by testing R.R. with sets of whole and half shapes presented tachistoscopically and asking him to report what he had seen. When R.R. viewed whole shapes he correctly reported seeing a whole shape on every trial. However, R.R. often reported seeing right half objects as whole, whereas he was much less prone to report left half objects as perceptually whole. We discuss the nature of this perceptual completion, and conclude that both scan paths and completion are consequences of object-based neglect, not its causes.