Saskia Ibelings

Measures of speech intelligibility in noise show limited correspondence with difficulties people with hearing loss report from daily life. This mismatch suggests that standard measurement conditions do not sufficiently capture aspects that are relevant for speech perception, such as dip listening and spatial release from masking. In the present study we developed and evaluated a test condition that incorporates these aspects and compared it with a standard condition. Speech intelligibility was measured in 100 participants with normal hearing (NH, N=17) and hearing loss (HL, N=83) ranging from mild to severe. Measurements were conducted using the German matrix sentence test (OLSA) in the standard condition with frontal presentation of stationary noise co-located with the target speech, and the proposed condition with fluctuating, speech-like maskers spatially separated (±60°) from the target. Stimuli were presented via headphones using virtual acoustics. Tests were performed unaided and with individualized amplification. The proposed condition revealed reduced speech intelligibility also for listeners with HL that showed close-to-normal speech intelligibility in the standard condition. With individualized amplification, more listeners with HL showed reduced speech intelligibility compared to NH listeners than in the standard condition. Benefit of amplification varied widely across individuals with similar hearing thresholds, with some listeners showing little or no benefit. The advantages of the proposed condition were driven by masker fluctuations rather than by spatial separation of sound sources. These findings demonstrate that speech intelligibility measurements incorporating fluctuating maskers provide potentially relevant information beyond standard assessments and can support a more individualized assessment of hearing loss.

In speech audiometry, the speech-recognition threshold (SRT) is usually established by adjusting the signal-to-noise ratio (SNR) until 50% of the words or sentences are repeated correctly. However, these conditions are rarely encountered in everyday situations. Therefore, for a group of 15 young participants with normal hearing and a group of 12 older participants with hearing impairment, speech-recognition scores were determined at SRT and at four higher SNRs using several stationary and fluctuating maskers. Participants’ verbal responses were recorded, and participants were asked to self-report their listening effort on a categorical scale (self-reported listening effort, SR-LE). The responses were analyzed using an Automatic Speech Recognizer (ASR) and compared to the results of a human examiner. An intraclass correlation coefficient of r = .993 for the agreement between their corresponding speech-recognition scores was observed. As expected, speech-recognition scores increased with increasing SNR and decreased with increasing SR-LE. However, differences between speech-recognition scores for fluctuating and stationary maskers were observed as a function of SNR, but not as a function of SR-LE. The verbal response time (VRT) and the response speech rate (RSR) of the listeners’ responses were measured using an ASR. The participants with hearing impairment showed significantly lower RSRs and higher VRTs compared to the participants with normal hearing. These differences may be attributed to differences in age, hearing, or both. With increasing SR-LE, VRT increased and RSR decreased. The results show the possibility of deriving a behavioral measure, VRT, measured directly from participants’ verbal responses during speech audiometry, as a proxy for SR-LE.

Speech-recognition tests are widely used in both clinical and research audiology. The purpose of this study was the development of a novel speech-recognition test that combines concepts of different speech-recognition tests to reduce training effects and allows for a large set of speech material. The new test consists of four different words per trial in a meaningful construct with a fixed structure, the so-called phrases. Various free databases were used to select the words and to determine their frequency. Highly frequent nouns were grouped into thematic categories and combined with related adjectives and infinitives. After discarding inappropriate and unnatural combinations, and eliminating duplications of (sub-)phrases, a total number of 772 phrases remained. Subsequently, the phrases were synthesized using a text-to-speech system. The synthesis significantly reduces the effort compared to recordings with a real speaker. After excluding outliers, measured speech-recognition scores for the phrases with 31 normal-hearing participants at fixed signal-to-noise ratios (SNR) revealed speech-recognition thresholds (SRT) for each phrase varying up to 4 dB. The median SRT was −9.1 dB SNR and thus comparable to existing sentence tests. The psychometric function's slope of 15 percentage points per dB is also comparable and enables efficient use in audiology. Summarizing, the principle of creating speech material in a modular system has many potential applications.

Speech-recognition tests are an important component of audiology. However, the development of such tests can be time consuming. The aim of this study was to investigate whether a Text-To-Speech (TTS) system can reduce the cost of development, and whether comparable results can be achieved in terms of speech recognition and listening effort. For this, the everyday sentences of the German Göttingen sentence test were synthesized for both a female and a male speaker using a TTS system. In a preliminary study, this system was rated as good, but worse than the natural reference. Due to the Covid-19 pandemic, the measurements took place online. Each set of speech material was presented at three fixed signal-to-noise ratios. The participants’ responses were recorded and analyzed offline. Compared to the natural speech, the adjusted psychometric functions for the synthetic speech, independent of the speaker, resulted in an improvement of the speech-recognition threshold (SRT) by approximately 1.2 dB. The slopes, which were independent of the speaker, were about 15 percentage points per dB. The time periods between the end of the stimulus presentation and the beginning of the verbal response (verbal response time) were comparable for all speakers, suggesting no difference in listening effort. The SRT values obtained in the online measurement for the natural speech were comparable to published data. In summary, the time and effort for the development of speech-recognition tests may be significantly reduced by using a TTS system. This finding provides the opportunity to develop new speech tests with a large amount of speech material.