Neglect between but not within auditory objects.

Unilateral neglect is frequently characterized by the presence of extinction, which is a lack of awareness to contralesional visual stimuli in the presence of those further towards the ipsilesional side. It has been established that this visual extinction can be reduced if the stimuli are grouped together into a single object. However, attention between and within auditory objects has never before been studied. We demonstrate for the first time that unilateral neglect--hitherto thought primarily to be a disorder of visuospatial processing-- involves a specific deficit in allocating attention between auditory objects separated only in time and not in space. Importantly, this deficit is restricted to comparisons between sounds: the patients' ability to make within-sound comparisons is similar to that of controls. These differences cannot be explained in terms of different time spans over which comparisons must be made. The results suggest unilateral neglect is linked to--if not actually determined by--a reduction in attentional capacity in both the visual and auditory domains, and across the dimensions of both space and time. The findings have potential clinical applications.