A speech-in-noise test which uses digit triplets in steady-state speech noise was developed. The test measures primarily the auditory, or bottom-up, speech recognition abilities in noise. Digit triplets were formed by concatenating single digits spoken by a male speaker. Level corrections were made to individual digits to create a set of homogeneous digit triplets with steep speech recognition functions. The test measures the speech reception threshold (SRT) in long-term average speech-spectrum noise via a 1-up, 1-down adaptive procedure with a measurement error of 0.7 dB. One training list is needed for naive listeners. No further learning effects were observed in 24 subsequent SRT measurements. The test was validated by comparing results on the test with results on the standard sentences-in-noise test. To avoid the confounding of hearing loss, age, and linguistic skills, these measurements were performed in normal-hearing subjects with simulated hearing loss. The signals were spectrally smeared and/or low-pass filtered at varying cutoff frequencies. After correction for measurement error the correlation coefficient between SRTs measured with both tests equaled 0.96. Finally, the feasibility of the test was approved in a study where reference SRT values were gathered in a representative set of 1386 listeners over 60 years of age.

Speech reception thresholds (SRTs) for sentences were determined in stationary and modulated background noise for two age-matched groups of normal-hearing (N = 13) and hearing-impaired listeners (N = 21). Correlations were studied between the SRT in noise and measures of auditory and nonauditory performance, after which stepwise regression analyses were performed within both groups separately. Auditory measures included the pure-tone audiogram and tests of spectral and temporal acuity. Nonauditory factors were assessed by measuring the text reception threshold (TRT), a visual analogue of the SRT, in which partially masked sentences were adaptively presented. Results indicate that, for the normal-hearing group, the variance in speech reception is mainly associated with nonauditory factors, both in stationary and in modulated noise. For the hearing-impaired group, speech reception in stationary noise is mainly related to the audiogram, even when audibility effects are accounted for. In modulated noise, both auditory (temporal acuity) and nonauditory factors (TRT) contribute to explaining interindividual differences in speech reception. Age was not a significant factor in the results. It is concluded that, under some conditions, nonauditory factors are relevant for the perception of speech in noise. Further evaluation of nonauditory factors might enable adapting the expectations from auditory rehabilitation in clinical settings.

The TRT test, a visual analogue of the SRT test, has been developed to measure the variance in speech-in-noise comprehension associated with modality-aspecific cognitive skills. In future research, normative data of the TRT test should be developed. It would also be interesting to measure TRTs of individuals experiencing difficulties understanding speech.