Sound stimulus qualities and severe auditory neglect.

We report the case of a patient who developed severe left auditory neglect following a cerebral vascular accident with infarction of areas in the frontal, temporal, and parietal lobes of the right hemisphere. The severity of neglect was documented using pure tones, speech, and environmental stimuli, administered binaurally and dichotically. Acuity examination and unilateral presentation of stimuli allowed exclusion of primary hearing deficit. A dichotic word test was used to evaluate the effects of implicit and explicit cuing. Contrary to our expectations, implicit semantic cues did not attenuate the neglect, and explicit manipulation of sound volume, consisting of increasing the volume in the left ear while maintaining right ear volume at a minimum did not increase the perception of neglected stimuli on the left. Explicit commands to selectively attend to the left ear also failed to improve left ear perception. These findings suggest that some manifestations of auditory neglect are not affected by attributes of the sound stimulus. Furthermore, the finding that manipulation of sound volume had no influence on the neglect supports the hypothesis that sound volume is perceived by the brain as encoded information and not as a simple analogue representation of sound magnitude mediated by variance in the firing rate of neurons in the auditory nerve.