Spatial release from masking in children with bilateral cochlear implants and with normal hearing: Effect of target-interferer similarity

Abstract

In complex auditory environments, it is often difficult to separate a target talker from interfering speech. For normal hearing (NH) adult listeners, similarity between the target and interfering speech leads to increased difficulty in separating them; that is, informational masking occurs due to confusability of the target and interferers. This study investigated performance of children with bilateral cochlear implants (BiCIs) when target and interferers were either same-sex (male) talkers, or different-sex talkers (male target, female interferer). Comparisons between children with BiCIs and NH, when matched for age, were also conducted. Speech intelligibility was measured for target and interferers spatially co-located, or spatially separated with the interferers positioned symmetrically (+90° and -90°) or asymmetrically (both at +90°, right). Spatial release from masking (SRM) was computed as the difference between co-located and separated conditions. Within group BiCI comparisons revealed that in the co-located condition speech intelligibility was worse with the same-sex vs different-sex stimuli. There was also a trend for more SRM with the same-sex vs different-sex stimuli. When comparing BiCI to NH listeners, SRM was larger for the NH groups, suggesting that NH children are better able to make use of spatial cues to improve speech understanding in noise.

FIG. 1.

The overall average spectrum are plotted for the target and interfering stimuli. The dashed black line represents the target stimuli. The solid lines represent the interfering stimuli (gray line = female interferers, black line = male interferers).

FIG. 2.

Mean (±SD) SRTs are plotted for each group in each condition with both the male and female interferers. The gray circles represent SRTs in the quiet condition. Filled symbols represent SRTs with the male interferers. Open symbols represent SRTs with the female interferers. Within each group, each condition is represented by a different symbol (square: front, triangle: 90A, diamond: 90S). Significant differences within condition are indicated with an asterisk.

FIG. 3.

Mean (±SD) SRTs are shown for each group in each condition (i.e., quiet, front, asymmetrical, symmetrical). Significant differences are bracketed and indicated with an asterisk. Solid brackets indicate significant differences within hearing type (i.e., A vs B). Dashed brackets indicate differences between hearing type (i.e., NH vs BiCI).

FIG. 4.

SRM values for asymmetrical and symmetrical conditions are compared for each individual listener group [(A) BiCI-A, (B) BiCI-B, (C) NH-A, (D) NH-B, (E) Adult]. Each data point represents SRM for an individual listener. The squares represent SRM with the male interferers, and the triangles represent SRM with the female interferers. The diagonal line corresponds to equivalent SRM in the asymmetrical and symmetrical conditions.

FIG. 5.

Mean (±SD) SRM values are plotted for each group (i.e., BiCI-A, BiCI-B, NH-A, NH-B, Adult) for both the male (5A) and female (5B) interferers. Black bars represent asymmetrical SRM. Gray bars represent symmetrical SRM. Significant differences are bracketed and indicated with an asterisk. Dashed brackets indicate difference between hearing type (i.e., NH vs BiCI).