Comparison of fluctuating maskers for speech recognition tests

Objective: To investigate the extent to which temporal gaps, temporal fine structure, and comprehensibility of the masker affect masking strength in speech recognition experiments. Design: Seven different masker types with Dutch speech materials were evaluated. Amongst these maskers were the ICRA-5 fluctuating noise, the international speech test signal (ISTS), and competing talkers in Dutch and Swedish. Study Sample: Normal-hearing and hearing-impaired subjects. Results: The normal-hearing subjects benefited from both temporal gaps and temporal fine structure in the fluctuating maskers. When the competing talker was comprehensible, performance decreased. The ISTS masker appeared to cause a large informational masking component. The stationary maskers yielded the steepest slopes of the psychometric function, followed by the modulated noises, followed by the competing talkers. Although the hearing-impaired group was heterogeneous, their data showed similar tendencies, but sometimes to a lesser extent, depending on individuals' hearing impairment. Conclusions: If measurement time is of primary concern non-modulated maskers are advised. If it is useful to assess release of masking by the use of temporal gaps, a fluctuating noise is advised. If perception of temporal fine structure is being investigated, a foreign-language competing talker is advised.