Sentence perception in listening conditions having similar speech intelligibility indices

Objective: The objective of this study was to examine the relation between bandwidth and speech perception in normally hearing adults and children at a single value of the Speech Intelligibility Index (SII). Design: The SII of meaningful and nonsense sentences were held constant for each of three bandwidths to test the hypothesis that perception would be equivalent in each condition. The sentences were filtered to produce three bandwidth conditions (low-pass cut-off frequency: 0.8, 1.25, 2.5 kHz) and the sensation level within each bandwidth was adjusted to produce a similar SII (0.430.48). Sentences were presented in broadband noise to facilitate equivalent audibility across subjects in each bandwidth condition. Study sample: Participants were 20 adults between the ages of 19 and 47 years and 20 eight-year-old children. All participants had normal hearing. Results and conclusion: Contrary to the hypothesis, performance of both groups increased significantly as bandwidth increased. Significant main effects of group and sentence type were also found. These results indicate that performance was governed largely by the bandwidth of the stimuli and that those effects were not represented well in the SII.