RESEARCH ARTICLE Auditory Spatial Discrimination and the Mismatch Negativity Response in Hearing- Impaired Individuals

The aims of the present study were to investigate the ability of hearing-impaired (HI) individ-uals with different binaural hearing conditions to discriminate spatial auditory-sources at the midline and lateral positions, and to explore the possible central processing mechanisms by measuring the minimal audible angle (MAA) and mismatch negativity (MMN) response. To measure MAA at the left/right 0°, 45 ° and 90 ° positions, 12 normal-hearing (NH) participants and 36 patients with sensorineural hearing loss, which included 12 patients with symmetri-cal hearing loss (SHL) and 24 patients with asymmetrical hearing loss (AHL) [12 with unilat-eral hearing loss on the left (UHLL) and 12 with unilateral hearing loss on the right (UHLR)] were recruited. In addition, 128-electrode electroencephalography was used to record the MMN response in a separate group of 60 patients (20 UHLL, 20 UHLR and 20 SHL patients) and 20 NH participants. The results showed MAA thresholds of the NH participants to be significantly lower than the HI participants. Also, a significantly smaller MAA threshold was obtained at the midline position than at the lateral position in both NH and SHL groups. How-ever, in the AHL group, MAA threshold for the 90 ° position on the affected side was signifi