Clear speech and lexical competition in younger and older adult listeners

The role of speech style, frequency, and density in recognition memory for spoken words

What determines whether listeners remember a spoken word? The Effortfulness Hypothesis claims that memory is modulated by a word's intelligibility during real-time processing, while the Distinctiveness Hypothesis claims that it is modulated by a word's distinguishing characteristics. We tested these differing predictions using American English words that varied along three dimensions known to affect both intelligibility and distinctiveness: speech style (clear versus casual), frequency (high versus low), and neighborhood density (high versus low). In a recognition memory experiment, participants (n = 66) listened to a set of study words, and then gave yes/no judgments to indicate whether or not they had heard the word earlier. Results showed that those words which exhibited distinctive characteristics - whether due to clear speech style, low frequency, or low density - were remembered better. The finding supports the Distinctiveness Hypothesis, suggesting that our capacity for remembering words relies on their distinctiveness, rather than on our capacity for recognizing them in real time.

Spread the Word: Enhancing Replicability of Speech Research Through Stimulus Sharing

PURPOSE

The ongoing replication crisis within and beyond psychology has revealed the numerous ways in which flexibility in the research process can affect study outcomes. In speech research, examples of these "researcher degrees of freedom" include the particular syllables, words, or sentences presented; the talkers who produce the stimuli and the instructions given to them; the population tested; whether and how stimuli are matched on amplitude; the type of masking noise used and its presentation level; and many others. In this research note, we argue that even seemingly minor methodological choices have the potential to affect study outcomes. To that end, we present a reanalysis of six existing data sets on spoken word identification in noise to assess how differences in talkers, stimulus processing, masking type, and listeners affect identification accuracy.

CONCLUSIONS

Our reanalysis revealed relatively low correlations among word identification rates across studies. The data suggest that some of the seemingly innocuous methodological details that differ across studies-details that cannot possibly be reported in text given the idiosyncrasies inherent to speech-introduce unknown variability that may affect replicability of our findings. We therefore argue that publicly sharing stimuli is a crucial step toward improved replicability in speech research.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.21985907.

Effect of telepractice on pediatric cochlear implant users and provider vowel space: A preliminary report

Clear speaking styles are goal-oriented modifications in which talkers adapt acoustic-phonetic characteristics of speech to compensate for communication challenges. Do children with hearing loss and a clinical provider modify speech characteristics during telepractice to adjust for remote communication? The study examined the effect of telepractice (tele-) on vowel production in seven (mean age 4:11 years, SD 1:2 years) children with cochlear implants (CIs) and a provider. The first (F1) and second (F2) formant frequencies of /i/, /ɑ/, and /u/ vowels were measured in child and provider speech during one in-person and one tele-speech-language intervention, order counterbalanced. Child and provider vowel space areas (VSA) were calculated. The results demonstrated an increase in F2 formant frequency for /i/ vowel in child and provider speech and an increase in F1 formant frequency for /ɑ/ vowel in the provider speech during tele- compared to in-person intervention. An expansion of VSA was found in child and provider speech in tele- compared to in-person intervention. In children, the earlier age of CI activation was associated with larger VSA in both tele- and in-person intervention. The results suggest that the children and the provider adjust vowel articulation in response to remote communication during telepractice.

Intelligibility of Noise-Adapted and Clear Speech in Energetic and Informational Maskers for Native and Nonnative Listeners

PURPOSE

This study explored clear speech (CS) and noise-adapted speech (NAS) intelligibility benefits for native and nonnative English listeners. It also examined how the two speaking style adaptations interact with maskers that vary from purely energetic to largely informational at different signal-to-noise ratios (SNRs).

METHOD

Materials consisted of 40 sentences produced by 10 young adult talkers in a conversational and a clear speaking style under two conditions: (a) in quiet and (b) in response to speech-shaped noise (SSN) played over headphones (NAS). Young adult native (Experiment 1) and nonnative (Experiment 2) English listeners heard target sentences presented in two-talker (2T) babble, six-talker (6T) babble, or SSN and at an "easier" and a "harder" SNR.

RESULTS

When talkers produced CS and NAS, word recognition accuracy was significantly improved for both listener groups. The largest intelligibility benefit was obtained for the CS produced in response to noise (CS+NAS). Overall accuracy was highest in 2T babble. Accuracy was higher in SSN than in 6T babble for nonnative listeners at both levels of listening difficulty but only at a more difficult SNR for native listeners. Listeners benefited from CS and NAS most in the presence of SSN and least in 2T babble. When SNRs were the same for the two listener groups, native listeners outperformed nonnative listeners in almost all listening conditions, but nonnative listeners benefited more from CS and NAS in 6T babble than native listeners did.

CONCLUSIONS

Combined speaking style enhancements, CS+NAS, provided the largest intelligibility increases for native and nonnative listeners in all listening conditions. The results add to the body of evidence supporting speech-oriented, behavioral therapy techniques for maximizing speech intelligibility in everyday listening situations.

Clear versus casual consonant identification by hearing-impaired and normal-hearing listeners

Hearing-impaired (HI) listeners who benefit from hearing-aid use in quiet often continue to have difficulty understanding speech in noise. Requesting talkers to speak clearly is one strategy to overcome this deficit. Paradoxically, one feature of clear speech is a shift to higher frequencies, which may move speech energy into a frequency range that is inaudible or more distorted for some HI listeners. Casual (or conversational) speech, on the other hand, may shift speech energy into a lower frequency range that is more audible or less distorted. This study examined the intelligibility of 21 amplified, casually- and clearly-spoken, US English coda consonants in nonsense syllables for 10 normal-hearing (NH) and 17 HI listeners. Most clear-speech consonants yielded higher recognition scores as expected. However, certain phonological processes common in casual speech, such as palatalization of higher frequency alveolar into lower frequency postalveolar consonants, generated significantly higher scores than their clear counterparts for some HI listeners in noise. These results have implications for coaching conversational partners of aided HI listeners. For the military, talkers can be instructed how to speak to Service members with hearing loss or in noisy environments.

Speaking Clearly for Older Adults With Normal Hearing: The Role of Speaking Rate

Purpose Talkers typically use a slow speaking rate when producing clear speech, a speaking style that has been widely shown to improve intelligibility over conversational speech in difficult communication environments. With training, however, talkers can learn to produce a form of clear speech at normal speaking rates that provides young listeners with normal hearing much of the same intelligibility benefit. The purpose of this study was to determine if older listeners with normal hearing can also obtain an intelligibility benefit from clear speech at normal rates. Method Eight older listeners (55-68 years of age) with normal hearing were presented with nonsense sentences from 4 talkers in a background of speech-shaped noise (signal-to-noise ratio = 0 dB). Intelligibility (percent correct key words) was evaluated for conversational and clear speech produced at 2 speaking rates (normal and slow), for a total of 4 conditions: conv/normal, conv/slow, clear/normal, and clear/slow. Results As expected, the clear/slow speaking condition provided a large and robust intelligibility advantage (23 points) over conv/normal speech. The conv/slow condition provided almost as much benefit on average (21 points) but was highly variable across talkers. Notably, the clear/normal speaking condition provided the same size intelligibility advantage (14 points), previously reported for young listeners with normal hearing (Krause & Braida, 2002), thus extending the benefit of clear speech at normal speaking rates to older normal-hearing listeners. Conclusions Applications based on clear/normal speech (e.g., signal processing approaches for hearing aids) have the potential to provide comparable intelligibility improvements to older and younger listeners alike.

Different Responses to Altered Auditory Feedback in Younger and Older Adults Reflect Differences in Lexical Bias

Purpose Previous work has found that both young and older adults exhibit a lexical bias in categorizing speech stimuli. In young adults, this has been argued to be an automatic influence of the lexicon on perceptual category boundaries. Older adults exhibit more top-down biases than younger adults, including an increased lexical bias. We investigated the nature of the increased lexical bias using a sensorimotor adaptation task designed to evaluate whether automatic processes drive this bias in older adults. Method A group of older adults ( n = 27) and younger adults ( n = 35) participated in an altered auditory feedback production task. Participants produced target words and nonwords under altered feedback that affected the 1st formant of the vowel. There were 2 feedback conditions that affected the lexical status of the target, such that target words were shifted to sound more like nonwords (e.g., less-liss) and target nonwords to sound more like words (e.g., kess-kiss). Results A mixed-effects linear regression was used to investigate the magnitude of compensation to altered auditory feedback between age groups and lexical conditions. Over the course of the experiment, older adults compensated (by shifting their production of 1st formant) more to altered auditory feedback when producing words that were shifted toward nonwords ( less-liss) than when producing nonwords that were shifted toward words ( kess-kiss). This is in contrast to younger adults who compensated more to nonwords that were shifted toward words compared to words that were shifted toward nonwords. Conclusion We found no evidence that the increased lexical bias previously observed in older adults is driven by a greater sensitivity to top-down lexical influence on perceptual category boundaries. We suggest the increased lexical bias in older adults is driven by postperceptual processes that arise as a result of age-related cognitive and sensory changes.