Measurement and optimisation of the perceptual equivalence of the Dutch consonant-vowel-consonant (CVC) word lists using synthetic speech and list pairs.

OBJECTIVES: (1) to determine whether the standard Dutch word lists for speech audiometry are equally intelligible in normal-hearing listeners (Experiment 1), (2) to investigate whether synthetic speech can be used to create word lists (Experiment 1) and (3) to determine whether the list effect found in Experiment 1 can be reduced by combining two lists into pairs (Experiment 2). DESIGN: Participants performed speech tests in quiet with the original (natural) and synthetic word lists (Experiment 1.). In Experiment 2, new participants performed speech tests with list pairs from the original lists constructed from the results of Experiment 1. STUDY SAMPLES: Twenty-four and twenty-eight normal-hearing adults. RESULTS: There was a significant list effect in the natural speech lists; not in the synthetic speech lists. Variability in intelligibility was significantly higher in the former, with list differences up to 20% at fixed presentation levels. The 95% confidence interval of a list with a score of approximately 70% is around 10%-points wider than of a list pair. CONCLUSIONS: The original Dutch word lists show large variations in intelligibility. List effects can be reduced by combining two lists per condition. Synthetic speech is a promising alternative to natural speech in speech audiometry in quiet.

Sensitivity of the antiphasic digits-in-noise test to simulated unilateral and bilateral conductive hearing loss.

OBJECTIVES: The objective of this study is (1) to assess whether the presentation level of the antiphasic digits-in-noise (DIN) test affects the speech recognition threshold (SRT), (2) to evaluate how accurately simulated unilateral and bilateral conductive hearing loss is detected (CHL) and (3) to determine whether increasing the presentation level normalises the antiphasic DIN SRT. DESIGN: Participants performed antiphasic and diotic DINs at different presentation levels with unilateral, bilateral or no earplugs. STUDY SAMPLE: Twenty-four and twelve normal hearing adults. RESULTS: Without earplugs, antiphasic DIN SRTs did not differ between 60 and 80 dB SPL. At 60 dB SPL, the antiphasic DIN correctly classified 92% of the unilateral earplug cases; the diotic DIN 25%. The binaural intelligibility level difference did not differ between the no-earplug condition and the condition with bilateral earplugs when the presentation was increased with the attenuation level. CONCLUSIONS: In normal hearing participants, diotic and antiphasic DIN SRTs are independent of presentation level above a minimum level of 60 dB SPL. The antiphasic DIN is more sensitive than the diotic DIN for detecting unilateral CHL; not for bilateral CHL. The effect of CHL on DIN SRTs can be largely compensated by increasing the presentation level. Audibility plays an important role in the antiphasic and diotic DIN.

The Importance of Extended High-Frequency Speech Information in the Recognition of Digits, Words, and Sentences in Quiet and Noise.

OBJECTIVES: In pure-tone audiometry, hearing thresholds are typically measured up to 8 kHz. Recent research has shown that extended high-frequency (EHF; frequencies >8 kHz) speech information improves speech recognition. However, it is unclear whether the EHF benefit is present for different types of speech material. This study assesses the added value of EHF information for speech recognition in noise for digit triplets, consonant-vowel-consonant (CVC) words, and sentences; and for speech recognition in quiet for CVC. DESIGN: Twenty-four young adults with normal-hearing thresholds up to 16 kHz performed a listening experiment in quiet and in noise in a within-subject repeated measures design. Stimuli were presented monaurally. Steady state speech-shaped noise at a fixed signal to noise ratio was used for measurements in noise. Listening conditions varied only in terms of available EHF information. Stimuli were presented in three different conditions: (1) both speech and noise broadband, (2) speech broadband and noise low-pass filtered at 8 kHz, and (3) both speech and noise low-pass filtered at 8 kHz. In the speech-in-quiet experiment, stimuli (CVC) were high-pass filtered at 3 kHz and presented in two conditions: (1) with EHF information and (2) without EHF information. RESULTS: In the speech-in-noise experiment, for all speech material, the highest scores were achieved in the condition where the noise was low-pass filtered at 8 kHz and speech unfiltered; the lowest scores were obtained in the condition where both speech and noise were low-pass filtered at 8 kHz. Adding speech frequencies above 8 kHz improved the median recognition scores by 75.0%, 21.8%, and 23.8% for digit triplets, words, and sentences, respectively, at a fixed signal to noise ratio. In the speech-in-quiet experiment, median recognition scores were 7.8% higher in the condition where the EHF information was available, as opposed to when it was not. CONCLUSIONS: Speech information for frequencies above 8 kHz contributes to speech recognition in noise. It also contributes to speech recognition in quiet when information below 3 kHz is absent. Our results suggest that EHFs may be relevant in challenging listening conditions and should be measured in pure-tone audiometry to get a complete picture of a person's hearing. Further, results of speech recognition tests may vary when different recording and/or measurement equipment is used with different frequency responses above 8 kHz.