Effects of moderate cochlear hearing loss on the ability to benefit from temporal fine structure information in speech

Abstract

Speech reception thresholds (SRTs) were measured with a competing talker background for signals processed to contain variable amounts of temporal fine structure (TFS) information, using nine normal-hearing and nine hearing-impaired subjects. Signals (speech and background talker) were bandpass filtered into channels. Channel signals for channel numbers above a "cut-off channel" (CO) were vocoded to remove TFS information, while channel signals for channel numbers of CO and below were left unprocessed. Signals from all channels were combined. As a group, hearing-impaired subjects benefited less than normal-hearing subjects from the additional TFS information that was available as CO increased. The amount of benefit varied between hearing-impaired individuals, with some showing no improvement in SRT and one showing an improvement similar to that for normal-hearing subjects. The reduced ability to take advantage of TFS information in speech may partially explain why subjects with cochlear hearing loss get less benefit from listening in a fluctuating background than normal-hearing subjects. TFS information may be important in identifying the temporal "dips" in such a background.

FIG. 1

Air conduction audiometric thresholds of the test ears of the hearing-impaired subjects for experiments one and two. The ages of the subjects (in years) are shown in parentheses.

FIG. 2

Excitation levels of the target speech (solid lines) and excitation levels at threshold (dashed lines) for individual hearing-impaired subjects. Excitation levels for normal-hearing subjects are shown for comparison in the bottom-right panel.

FIG. 3

Mean SRTs for normal-hearing and hearing-impaired subjects, plotted as a function of CO/N. The frequency corresponding to CO/N is shown along the top axis. Error bars show ± one standard deviation across subjects.

FIG. 4

Individual SRTs for the hearing-impaired subjects, plotted as a function of CO/N. Mean SRTs measured for the normal-hearing subjects are shown in the bottom-right panel for comparison.

FIG. 5

Mean SRTs for normal-hearing subjects (left) and hearing-impaired subjects (right), plotted as a function of CO/N. Error bars show ± one standard deviation across subjects.