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

Abstract

The aims of the present study were to investigate the ability of hearing-impaired (HI) individuals 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 symmetrical hearing loss (SHL) and 24 patients with asymmetrical hearing loss (AHL) [12 with unilateral 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. However, in the AHL group, MAA threshold for the 90° position on the affected side was significantly smaller than the MMA thresholds obtained at other positions. Significantly reduced amplitudes and prolonged latencies of the MMN were found in the HI groups compared to the NH group. In addition, contralateral activation was found in the UHL group for sounds emanating from the 90° position on the affected side and in the NH group. These findings suggest that the abilities of spatial discrimination at the midline and lateral positions vary significantly in different hearing conditions. A reduced MMN amplitude and prolonged latency together with bilaterally symmetrical cortical activations over the auditory hemispheres indicate possible cortical compensatory changes associated with poor behavioral spatial discrimination in individuals with HI.

Fig 1. (Color Online) A comparison of the MAA performances of the subjects with all hearing abilities at the midline (0°) and lateral (45° and 90°) positions.

Note: * there was a significant difference, i.e., p<0.05.

Fig 2. (Color Online) Response to standard and deviants at Fz and referenced mastoid site.

Note: “R” and “L” represent right and left, respectively.

Fig 3. (Color Online) A comparison of the grand average MMN responses of the subjects with different hearing abilities at the Fz electrode.

Note: the black arrow indicates the MMN response of the NH group; the red arrow indicates the MMN response of the HI group, and “R” and “L” represent right and left, respectively.

Fig 4. (Color Online) Grand-average difference waveforms at the referenced mastoid electrode.

Note: “R” and “L” represent right and left, respectively.

Fig 5. (Color Online) A topographic map based on the peak MMN responses of the subjects with different hearing abilities.