Effects of Vocabulary and Implicit Linguistic Knowledge on Speech Recognition in Adverse Listening Conditions

Examining listeners' perception of spoken words with different face masks

The COVID-19 pandemic made face masks part of daily life. While masks protect against the virus, it is important to understand the impact masks have on listeners' recognition of spoken words. We examined spoken word recognition under three different mask conditions (no mask; cloth mask; Kn95 mask) and in both easy (low density, high phonotactic probability) and hard (high density, low phonotactic probability) words in a lexical decision task. In Experiment 1, participants heard all words and nonwords under all three mask conditions. In Experiment 2, participants heard each word and nonword only once under one of the mask conditions. The reaction time and accuracy results were consistent between Experiments 1 and 2. The pattern of results was such that the no mask condition produced the fastest and most accurate responses followed by the Kn95 mask condition and the cloth mask condition, respectively. Furthermore, there was a trend towards a speed-accuracy trade-off with Word Type. Easy words produced faster but less accurate responses relative to hard words. The finding that cloth masks had a more detrimental impact on spoken word recognition than Kn95 masks is consistent with previous research, and the current results further demonstrate that this effect extends to individual word recognition tasks with only audio presentation.

A review of auditory processing and cognitive change during normal ageing, and the implications for setting hearing aids for older adults

Throughout our adult lives there is a decline in peripheral hearing, auditory processing and elements of cognition that support listening ability. Audiometry provides no information about the status of auditory processing and cognition, and older adults often struggle with complex listening situations, such as speech in noise perception, even if their peripheral hearing appears normal. Hearing aids can address some aspects of peripheral hearing impairment and improve signal-to-noise ratios. However, they cannot directly enhance central processes and may introduce distortion to sound that might act to undermine listening ability. This review paper highlights the need to consider the distortion introduced by hearing aids, specifically when considering normally-ageing older adults. We focus on patients with age-related hearing loss because they represent the vast majority of the population attending audiology clinics. We believe that it is important to recognize that the combination of peripheral and central, auditory and cognitive decline make older adults some of the most complex patients seen in audiology services, so they should not be treated as "standard" despite the high prevalence of age-related hearing loss. We argue that a primary concern should be to avoid hearing aid settings that introduce distortion to speech envelope cues, which is not a new concept. The primary cause of distortion is the speed and range of change to hearing aid amplification (i.e., compression). We argue that slow-acting compression should be considered as a default for some users and that other advanced features should be reconsidered as they may also introduce distortion that some users may not be able to tolerate. We discuss how this can be incorporated into a pragmatic approach to hearing aid fitting that does not require increased loading on audiology services.

The Application of Time-Frequency Masking To Improve Intelligibility of Dysarthric Speech in Background Noise

PURPOSE

Background noise reduces speech intelligibility. Time-frequency (T-F) masking is an established signal processing technique that improves intelligibility of neurotypical speech in background noise. Here, we investigated a novel application of T-F masking, assessing its potential to improve intelligibility of neurologically degraded speech in background noise.

METHOD

Listener participants (N = 422) completed an intelligibility task either in the laboratory or online, listening to and transcribing audio recordings of neurotypical (control) and neurologically degraded (dysarthria) speech under three different processing types: speech in quiet (quiet), speech mixed with cafeteria noise (noise), and speech mixed with cafeteria noise and then subsequently processed by an ideal quantized mask (IQM) to remove the noise.

RESULTS

We observed significant reductions in intelligibility of dysarthric speech, even at highly favorable signal-to-noise ratios (+11 to +23 dB) that did not impact neurotypical speech. We also observed significant intelligibility improvements from speech in noise to IQM-processed speech for both control and dysarthric speech across a wide range of noise levels. Furthermore, the overall benefit of IQM processing for dysarthric speech was comparable with that of the control speech in background noise, as was the intelligibility data collected in the laboratory versus online.

CONCLUSIONS

This study demonstrates proof of concept, validating the application of T-F masks to a neurologically degraded speech signal. Given that intelligibility challenges greatly impact communication, and thus the lives of people with dysarthria and their communication partners, the development of clinical tools to enhance intelligibility in this clinical population is critical.

Educational Information Improves Listener Attitudes Toward People With Dysarthria Secondary to Parkinson's Disease

PURPOSE

People with dysarthria have been rated as less confident and less likable and are often assumed by listeners to have reduced cognitive abilities relative to neurotypical speakers. This study explores whether educational information about dysarthria can shift these attitudes in a group of speakers with hypokinetic dysarthria secondary to Parkinson's disease.

METHOD

One hundred seventeen listeners were recruited via Amazon Mechanical Turk to transcribe sentences and rate the confidence, intelligence, and likability of eight speakers with mild hypokinetic dysarthria. Listeners were assigned to one of four conditions. In one condition, listeners were provided with no educational information prior to exposure to speakers with dysarthria (n = 29). In another condition, listeners were given educational statements from the American Speech-Language-Hearing Association website (n = 29). In a third condition, listeners were given additional information stating that dysarthria does not indicate reduced intelligence or understanding (n = 30). Finally, in a fourth condition, listeners only heard samples from neurotypical, age-matched adults (n = 29).

RESULTS

Results revealed statistically significant effects of educational statements on ratings of speakers' confidence, intelligence, and likability. However, educational statements did not affect listeners' transcription accuracy.

CONCLUSIONS

This study presents preliminary evidence that educational material can positively influence listener impressions of speakers with hypokinetic dysarthria, especially when it is explicitly stated that the disorder does not affect intelligence or understanding. This initial examination provides preliminary support for educational awareness campaigns and self-disclosure of communicative difficulties in people with mild dysarthria.

Effects of word familiarity and receptive vocabulary size on speech-in-noise recognition among young adults with normal hearing

Having a large receptive vocabulary benefits speech-in-noise recognition for young children, though this is not always the case for older children or adults. These observations could indicate that effects of receptive vocabulary size on speech-in-noise recognition differ depending on familiarity of the target words, with effects observed only for more recently acquired and less frequent words. Two experiments were conducted to evaluate effects of vocabulary size on open-set speech-in-noise recognition for adults with normal hearing. Targets were words acquired at 4, 9, 12 and 15 years of age, and they were presented at signal-to-noise ratios (SNRs) of -5 and -7 dB. Percent correct scores tended to fall with increasing age of acquisition (AoA), with the caveat that performance at -7 dB SNR was better for words acquired at 9 years of age than earlier- or later-acquired words. Similar results were obtained whether the AoA of the target words was blocked or mixed across trials. Differences in word duration appear to account for nonmonotonic effects of AoA. For all conditions, a positive correlation was observed between recognition and vocabulary size irrespective of target word AoA, indicating that effects of vocabulary size are not limited to recently acquired words. This dataset does not support differential assessment of AoA, lexical frequency, and other stimulus features known to affect lexical access.

Comparing Lexical Cues in Listener Processing of Dysarthria and Speech in Noise

Purpose The frequency of a word and its number of phonologically similar neighbors can dramatically affect how likely it is to be accurately identified in adverse listening conditions. This study compares how these two cues affect listeners' processing of speech in noise and dysarthric speech. Method Seven speakers with moderate hypokinetic dysarthria and eight healthy control speakers were recorded producing the same set of phrases. Statements from control speakers were mixed with noise at a level selected to match the intelligibility range of the speakers with dysarthria. A binomial mixed-effects model quantified the effects of word frequency and phonological density on word identification. Results The model revealed significant effects of word frequency (b = 0.37, SE = 0.12, p = .002) and phonological neighborhood density (b = 0.40, SE = 0.12, p = .001). There was no effect of speaking condition (i.e., dysarthric speech vs. speech in noise). However, a significant interaction was observed between speaking condition and word frequency (b = 0.26, SE = 0.04, p < .001). Conclusions The model's interactions indicated that listeners were more strongly influenced by the effects of word frequency when decoding moderate hypokinetic dysarthria as compared to speech in noise. Differences in listener reliance on lexical cues may have important implications for the selection of communication-based treatment strategies for speakers with dysarthria.

Introduction to the Special Issue: Select Papers From the Hearing Across the Lifespan (HEAL) 2018 Conference

[Figure: see text].