Auditory lateralisation deficits in neglect patients

Although visual deficits due to unilateral spatial neglect (USN) have been frequently described in the literature, fewer studies have been interested in directional hearing impairment in USN. The aim of this study was to explore sound lateralisation deficits in USN. Using a paradigm inspired by Tanaka et al. (1999), interaural time differences (ITD) were presented over headphones to give the illusion of a leftward or a rightward movement of sound. Participants were asked to respond "right" and "left" as soon as possible to indicate whether they heard the sound moving to the right or to the left side of the auditory space. We additionally adopted a single-case method to analyse the performance of 15 patients with right-hemisphere (RH) stroke and added two additional measures to underline sound lateralisation on the left side and on the right side. We included 15 patients with RH stoke (5 with a severe USN, 5 with a mild USN and 5 without USN) and 11 healthy age-matched participants. We expected to replicate findings of abnormal sound lateralisation in USN. However, although a sound lateralisation deficit was observed in USN, two different deficit profiles were identified. Namely, patients with a severe USN seemed to have left sound lateralisation impairment whereas patients with a mild USN seemed to be more influenced by a systematic bias in auditory representation with respect to body meridian axis (egocentric deviation). This latter profile was unexpected as sounds were manipulated with ITD and, thus, would not be perceived as coming from an external source of the head. Future studies should use this paradigm in order to better understand these two distinct profiles.