Spatial release from masking in normally hearing and hearing-impaired listeners as a function of the temporal overlap of competing talkers

Abstract

Listeners with sensorineural hearing loss are poorer than listeners with normal hearing at understanding one talker in the presence of another. This deficit is more pronounced when competing talkers are spatially separated, implying a reduced "spatial benefit" in hearing-impaired listeners. This study tested the hypothesis that this deficit is due to increased masking specifically during the simultaneous portions of competing speech signals. Monosyllabic words were compressed to a uniform duration and concatenated to create target and masker sentences with three levels of temporal overlap: 0% (non-overlapping in time), 50% (partially overlapping), or 100% (completely overlapping). Listeners with hearing loss performed particularly poorly in the 100% overlap condition, consistent with the idea that simultaneous speech sounds are most problematic for these listeners. However, spatial release from masking was reduced in all overlap conditions, suggesting that increased masking during periods of temporal overlap is only one factor limiting spatial unmasking in hearing-impaired listeners.

Figure 1

Left- and right-ear audiograms (crosses and circles, respectively) for each listener in the HI group.

Figure 2

Schematic illustration showing the temporal structure of the target (white) and masker (gray) sentences in the quiet training condition (top) as well as in the masked conditions with 0%, 50%, and 100% overlap.

Figure 3

Individual data for the nine listeners in the NH group. Each panel shows performance (in percent correct) for a different listener as a function of spatial configuration. The three lines in each panel represent the three overlap conditions (0%, black circles; 50%, gray squares; 100%, white triangles). Dashed lines at the top of each panel show quiet performance.

Figure 4

Individual data for the nine listeners in the HI group. Other details as per Fig. 3.

Figure 5

Individual data for the six listeners in the NHLP group. Other details as per Fig. 3.

Figure 6

Mean performance and SRM for the NH and HI groups (left column) and the NH subgroup without and with low-pass filtering (right column). The top and middle panels show performance (in percent correct) for the co-located and separated configurations, respectively. The bottom panel shows SRM (in percentage points—note the ordinate scale is different to upper panels). The three clusters of bars show results for the three overlap conditions. Bars represent mean results pooled across listeners and the error bars show ±1 standard deviation of the mean.

Figure 7

Error rates for the NH and HI groups. The left and right columns show data for the co-located and separated configurations, and the three rows show masker errors, order errors, and random errors. The three clusters of bars in each panel show the three overlap conditions. Bars show the mean error rates in percent of total trials, such that the different error rates add up to the total percentage of incorrect trials. The error bars show ±1 standard deviation of the mean.