Short-term implicit voice-learning leads to a Familiar Talker Advantage: The role of encoding specificity

Naive Listener Ratings of Speech Intelligibility Over the Course of Motor-Based Intervention in Children With Childhood Apraxia of Speech

PURPOSE

The aim of this study was to describe changes in speech intelligibility and interrater and intrarater reliability of naive listeners' ratings of words produced by young children diagnosed with childhood apraxia of speech (CAS) over a period of motor-based intervention (dynamic temporal and tactile cueing [DTTC]).

METHOD

A total of 120 naive listeners (i.e., listeners without experience listening to children with speech and/or language impairments; age range: 18-45 years) orthographically transcribed single-word productions by five children (age range: 2;6-3;11 [years;months]) across three time points over an intervention period (baseline, post-treatment, maintenance). Changes in intelligibility and interrater and intrarater reliability were examined within and across time points.

RESULTS

Speech intelligibility significantly increased in children with CAS over the course of treatment, and these gains were also maintained at 6 weeks posttreatment. There was poor-to-fair consistency between listeners (interrater reliability) and excellent consistency within listeners (intrarater reliability) in ratings of speech intelligibility within and across time points.

CONCLUSIONS

Motor-based intervention increases speech intelligibility following a period of DTTC treatment. Variability among naive listeners of speech intelligibility was also present, with intrarater reliability (within listeners) yielding greater consistency than interrater reliability (between listeners). The implications for including naive listeners as raters of speech intelligibility for research and clinical purposes are discussed.

Short Implicit Voice Training Affects Listening Effort During a Voice Cue Sensitivity Task With Vocoder-Degraded Speech

OBJECTIVES

Understanding speech in real life can be challenging and effortful, such as in multiple-talker listening conditions. Fundamental frequency (fo) and vocal-tract length (vtl) voice cues can help listeners segregate between talkers, enhancing speech perception in adverse listening conditions. Previous research showed lower sensitivity to fo and vtl voice cues when speech signal was degraded, such as in cochlear implant hearing and vocoder-listening compared to normal hearing, likely contributing to difficulties in understanding speech in adverse listening. Nevertheless, when multiple talkers are present, familiarity with a talker's voice, via training or exposure, could provide a speech intelligibility benefit. In this study, the objective was to assess how an implicit short-term voice training could affect perceptual discrimination of voice cues (fo+vtl), measured in sensitivity and listening effort, with or without vocoder degradations.

DESIGN

Voice training was provided via listening to a recording of a book segment for approximately 30 min, and answering text-related questions, to ensure engagement. Just-noticeable differences (JNDs) for fo+vtl were measured with an odd-one-out task implemented as a 3-alternative forced-choice adaptive paradigm, while simultaneously collecting pupil data. The reference voice either belonged to the trained voice or an untrained voice. Effects of voice training (trained and untrained voice), vocoding (non-vocoded and vocoded), and item variability (fixed or variable consonant-vowel triplets presented across three items) on voice cue sensitivity (fo+vtl JNDs) and listening effort (pupillometry measurements) were analyzed.

RESULTS

Results showed that voice training did not have a significant effect on voice cue discrimination. As expected, fo+vtl JNDs were significantly larger for vocoded conditions than for non-vocoded conditions and with variable item presentations than fixed item presentations. Generalized additive mixed models analysis of pupil dilation over the time course of stimulus presentation showed that pupil dilation was significantly larger during fo+vtl discrimination while listening to untrained voices compared to trained voices, but only for vocoder-degraded speech. Peak pupil dilation was significantly larger for vocoded conditions compared to non-vocoded conditions and variable items increased the pupil baseline relative to fixed items, which could suggest a higher anticipated task difficulty.

CONCLUSIONS

In this study, even though short voice training did not lead to improved sensitivity to small fo+vtl voice cue differences at the discrimination threshold level, voice training still resulted in reduced listening effort for discrimination among vocoded voice cues.

Intelligibility as a measure of speech perception: Current approaches, challenges, and recommendations

Intelligibility measures, which assess the number of words or phonemes a listener correctly transcribes or repeats, are commonly used metrics for speech perception research. While these measures have many benefits for researchers, they also come with a number of limitations. By pointing out the strengths and limitations of this approach, including how it fails to capture aspects of perception such as listening effort, this article argues that the role of intelligibility measures must be reconsidered in fields such as linguistics, communication disorders, and psychology. Recommendations for future work in this area are presented.

Implicit and explicit learning in talker identification

In the real world, listeners seem to implicitly learn talkers' vocal identities during interactions that prioritize attending to the content of talkers' speech. In contrast, most laboratory experiments of talker identification employ training paradigms that require listeners to explicitly practice identifying voices. Here, we investigated whether listeners become familiar with talkers' vocal identities during initial exposures that do not involve explicit talker identification. Participants were assigned to one of three exposure tasks, in which they heard identical stimuli but were differentially required to attend to the talkers' vocal identity or to the verbal content of their speech: (1) matching the talker to a concurrent visual cue (talker-matching); (2) discriminating whether the talker was the same as the prior trial (talker 1-back); or (3) discriminating whether speech content matched the previous trial (verbal 1-back). All participants were then tested on their ability to learn to identify talkers from novel speech content. Critically, we manipulated whether the talkers during this post-test differed from those heard during training. Compared to learning to identify novel talkers, listeners were significantly more accurate learning to identify the talkers they had previously been exposed to in the talker-matching and verbal 1-back tasks, but not the talker 1-back task. The correlation between talker identification test performance and exposure task performance was also greater when the talkers were the same in both tasks. These results suggest that listeners learn talkers' vocal identity implicitly during speech perception, even if they are not explicitly attending to the talkers' identity.

The Effect of Talker Familiarity on Sentence Recognition Accuracy in Complex Noise

The familiar talker advantage is the finding that a listener's ability to perceive and understand a talker is facilitated when the listener is familiar with the talker. However, it is unclear when the benefits of familiarity emerge and whether they strengthen over time. To better understand the time course of the familiar talker advantage, we assessed the effects of long-term, implicit voice learning on 89 young adults' sentence recognition accuracy in the presence of four-talker babble. A university professor served as the target talker in the experiment. Half the participants were students of the professor and familiar with her voice. The professor was a stranger to the remaining participants. We manipulated the listeners' degree of familiarity with the professor over the course of a semester. We used mixed effects modeling to test for the effects of the two independent variables: talker and hours of exposure. Analyses revealed a familiar talker advantage in the listeners after 16 weeks (∼32 h) of exposure to the target voice. These results imply that talker familiarity (outside of the confines of a long-term, familial relationship) seems to be a much quicker-to-emerge, reliable cue for bootstrapping spoken language perception than previous literature suggested.