Rotation or translation of auditory space in neglect? A case study of chronic right-sided neglect.

Egocentric models of neglect explain the lateralised omission of stimuli in neglect patients by an ipsilesional shift of a subjective reference frame. However, they differ in the direction of shift (rotation around the midsagittal plane versus translation in front/back space). We tested this hypothesis in a patient (AJ) with persistent right-sided neglect following a left temporo-parieto-occipital and hypoxic lesion and in six age-matched healthy subjects. AJ showed visual neglect in line bisection, size matching, reading and visual search. Auditory localization was tested by using two different psychophysical techniques based on binaurally simulated stimuli for the horizontal plane in front and back space. Eye position was continuously monitored during stimulus presentation in all subjects. AJ revealed a significant ipsilesional, leftward shift of his auditory subjective median plane (ASMP) in front space (mean: -22.6 degrees), and a rightward shift of the ASMP in back space (+14.5 degrees). This pattern of results was replicated with a different psychophysical technique in a retest 10 months later. The rotational shift of AJ's ASMP contrasted with normal performance in the healthy subjects. Monaural hearing deficits can not account for these differential findings as all subjects (including AJ) performed normally. In conclusion, a rotation of the egocentric spatial reference frame may occur in the auditory modality for right-sided neglect.