Bias in the perception of phonetic detail in children's speech: A comparison of categorical and continuous rating scales

Functional benefits of continuous vs. categorical listening strategies on the neural encoding and perception of noise-degraded speech

Acoustic information in speech changes continuously, yet listeners form discrete perceptual categories to ease the demands of perception. Being a more continuous/gradient as opposed to a more discrete/categorical listener may be further advantageous for understanding speech in noise by increasing perceptual flexibility and resolving ambiguity. The degree to which a listener's responses to a continuum of speech sounds are categorical versus continuous can be quantified using visual analog scaling (VAS) during speech labeling tasks. Here, we recorded event-related brain potentials (ERPs) to vowels along an acoustic-phonetic continuum (/u/ to /a/) while listeners categorized phonemes in both clean and noise conditions. Behavior was assessed using standard two alternative forced choice (2AFC) and VAS paradigms to evaluate categorization under task structures that promote discrete vs. continuous hearing, respectively. Behaviorally, identification curves were steeper under 2AFC vs. VAS categorization but were relatively immune to noise, suggesting robust access to abstract, phonetic categories even under signal degradation. Behavioral slopes were correlated with listeners' QuickSIN scores; shallower slopes corresponded with better speech in noise performance, suggesting a perceptual advantage to noise degraded speech comprehension conferred by a more gradient listening strategy. At the neural level, P2 amplitudes and latencies of the ERPs were modulated by task and noise; VAS responses were larger and showed greater noise-related latency delays than 2AFC responses. More gradient responders had smaller shifts in ERP latency with noise, suggesting their neural encoding of speech was more resilient to noise degradation. Interestingly, source-resolved ERPs showed that more gradient listening was also correlated with stronger neural responses in left superior temporal gyrus. Our results demonstrate that listening strategy modulates the categorical organization of speech and behavioral success, with more continuous/gradient listening being advantageous to sentential speech in noise perception.

Functional benefits of continuous vs. categorical listening strategies on the neural encoding and perception of noise-degraded speech

Acoustic information in speech changes continuously, yet listeners form discrete perceptual categories to ease the demands of perception. Being a more continuous/gradient as opposed to a discrete/categorical listener may be further advantageous for understanding speech in noise by increasing perceptual flexibility and resolving ambiguity. The degree to which a listener's responses to a continuum of speech sounds are categorical versus continuous can be quantified using visual analog scaling (VAS) during speech labeling tasks. Here, we recorded event-related brain potentials (ERPs) to vowels along an acoustic-phonetic continuum (/u/ to /a/) while listeners categorized phonemes in both clean and noise conditions. Behavior was assessed using standard two alternative forced choice (2AFC) and VAS paradigms to evaluate categorization under task structures that promote discrete (2AFC) vs. continuous (VAS) hearing, respectively. Behaviorally, identification curves were steeper under 2AFC vs. VAS categorization but were relatively immune to noise, suggesting robust access to abstract, phonetic categories even under signal degradation. Behavioral slopes were positively correlated with listeners' QuickSIN scores, suggesting a behavioral advantage for speech in noise comprehension conferred by gradient listening strategy. At the neural level, electrode level data revealed P2 peak amplitudes of the ERPs were modulated by task and noise; responses were larger under VAS vs. 2AFC categorization and showed larger noise-related delay in latency in the VAS vs. 2AFC condition. More gradient responders also had smaller shifts in ERP latency with noise, suggesting their neural encoding of speech was more resilient to noise degradation. Interestingly, source-resolved ERPs showed that more gradient listening was also correlated with stronger neural responses in left superior temporal gyrus. Our results demonstrate that listening strategy (i.e., being a discrete vs. continuous listener) modulates the categorical organization of speech and behavioral success, with continuous/gradient listening being more advantageous to speech in noise perception.

Perceptual measurement of articulatory goodness in young children: Relationships with age, speech sound acquisition, and intelligibility

Speech language pathologists regularly use perceptual methods in clinical practice to assess children's speech. In this study, we examined relationships between measures of speech intelligibility, clinical articulation test results, age, and perceptual ratings of articulatory goodness for children. We also examined the extent to which established measures of intelligibility and clinical articulation test results predicted articulatory goodness ratings, and whether goodness ratings were influenced by intelligibility. A sample of 164 (30-47 months) typically developing children provided speech samples and completed a standardised articulation test. Single word intelligibility scores and ratings of articulatory goodness were gathered from 328 naïve listeners; scores on a standardised articulation test were obtained from each child. Bivariate Pearson correlation, linear regression, and linear mixed effects modelling were used for analysis. Results showed that articulatory goodness ratings had the highest correlation with intelligibility, followed by age, followed by articulation score. Age and clinical articulation scores were both significant predictors of goodness ratings, but articulation scores made only a small contribution to prediction. Articulatory goodness ratings were substantially lower for unintelligible words compared to intelligible words, but articulatory goodness scores increased with age at the same rate for unintelligible and intelligible words. Perceptual ratings of articulatory goodness are sensitive to developmental changes in speech production (regardless of intelligibility) and yield a different kind of information than clinical articulation scores from standardised measures.

Auditory-perceptual evaluation with visual analogue scale: feasibility and preliminary evidence of ultrasound visual feedback treatment of Finnish [r]

Accumulating evidence suggests that ultrasound visual feedback increases the treatment efficacy for persistent speech sound errors. However, the available evidence is mostly from English. This is a feasibility study of ultrasound visual feedback for treating distortion of Finnish [r]. We developed a web-based application for auditory-perceptual judgement. We investigated the impact of listener's experience on perceptual judgement and the intra-rater reliability of listeners. Four boys (10-11 years) with distortion of [r], otherwise typical development, partook in eight ultrasound treatment sessions. In total, 117 [r] samples collected at pre- and post-intervention were judged with visual analogue scale (VAS) by two listener groups: five speech and language therapists (SLTs) and six SLT students. We constructed a linear mixed-effects model with fixed effects for time and listener group and several random effects. Our findings indicate that measurement time had a significant main effect on judgement results, χ² = 78.82, p < 0.001. Effect of listener group was non-significant, but a significant main effect of interaction of group × time, χ² = 6.33, p < 0.012 was observed. We further explored the effect of group with nested models, and results revealed a non-significant effect of group. The average intra-rater correlation of the 11 listeners was 0.83 for the pre-intervention samples and 0.92 for post-intervention showing a good or excellent degree of agreement. Finnish [r] sound can be evaluated with VAS and ultrasound visual feedback is a feasible and promising method in treatment for distortion of [r], and its efficacy should be further assessed.

Individual Differences in Categorical Judgment of L2 Stops: A Link to Proficiency and Acoustic Cue-Weighting

This study investigated individual differences in Korean adult learners' categorical perception of L2 English stops with an aim to explore the relationship of gradient categorizations to perceptual sensitivity to acoustic cues and L2 proficiency. Korean young adult L2 learners of English (N = 49) participated in two speech perception tasks (visual analog scaling and forced-choice identification) in which they listened to English voiced and voiceless stops and Korean lax and aspirated stops with Voice Onset Time (VOT) and F0 manipulated to form a continuum. It was found that in both L1 and L2 stop perception, listeners' gradient category judgment was associated with greater reliance on language-specific redundant cues (i.e., F0 in L2 English and VOT in L1 Korean) and that in the perception of L2 stops, categorical listeners who tended to be less sensitive to F0 were the ones with a higher level of L2 English proficiency. The results suggest that the categorical manner of judging L2 stops reflects learners' better knowledge of L2-specific acoustic cue-weightings, based on which less relevant acoustic information is effectively suppressed.

Covert contrasts and categorical perception: a comparison of two measurement tools

This study considers adults' perception of subtle differences in the error productions of /r/ and /l/ in young children. Given that these two phonemes share a common substitution [w], the potential covert contrast between these three sounds was investigated. The utility of two perceptual rating scales was compared: a linear visual analogue scale (VAS) and a triangular scale that considered the possibility of covert contrast among /r,l,w/. Adult listeners rated speech productions from children with cochlear implants (CIs) and speech age-matched children with normal hearing (NH) as they produced VCV or CV productions with /r,l,w/ in syllable-initial position. Mahalanobis distances of the listener ratings for each stimulus on each rating scale were calculated for analysis. Ultimately, there was no difference between the ratings of the two speaker populations. However, there was a significant difference in the amount of variability captured with each scale. The triangular scale reliably captured more variability in the productions than the linear VAS. The significant effect of scale type on the spread of listeners' responses provides support for the claim that the type of rating system used can capture different aspects of a listener's perceptions, thereby suggesting that the type of rating system used in a study may significantly influence that study's findings.

The myth of categorical perception

Categorical perception (CP) is likely the single finding from speech perception with the biggest impact on cognitive science. However, within speech perception, it is widely known to be an artifact of task demands. CP is empirically defined as a relationship between phoneme identification and discrimination. As discrimination tasks do not appear to require categorization, this was thought to support the claim that listeners perceive speech solely in terms of linguistic categories. However, 50 years of work using discrimination tasks, priming, the visual world paradigm, and event related potentials has rejected the strongest forms of CP and provided little strong evidence for any form of it. This paper reviews the origins and impact of this scientific meme and the work challenging it. It discusses work showing that the encoding of auditory input is largely continuous, not categorical, and describes the modern theoretical synthesis in which listeners preserve fine-grained detail to enable more flexible processing. This synthesis is fundamentally inconsistent with CP. This leads to a different understanding of how to use and interpret the most basic paradigms in speech perception-phoneme identification along a continuum-and has implications for understanding language and hearing disorders, development, and multilingualism.

Clinical experience and categorical perception of children's speech

BACKGROUND

Accurate and detailed records of children's speech are a critical component of competent service delivery in speech-language pathology/speech and language therapy (SLP/SLT). Previous research has shown that during speech-sound acquisition, children gradually learn to produce sounds in adult-like manners. Continuous rating scales are a way to track this gradual learning.

AIMS

To examine whether clinical experience affects the ability and willingness to rate children's speech production using continuous rating scales.

METHODS & PROCEDURES

An online survey was administered to 81 US-based SLPs/SLTs, binned into more- and less-experienced groups, and 20 non-SLPs/SLTs. The survey included a speech-sound rating task in which participants rated the production of place of articulation in children's productions of word-initial /θ/, /s/, /ʃ/, /d/, /ɡ/, /t/ and /k/ on a nine-point equally appearing interval scale. We examined the extent to which these were accurate (i.e., the extent to which they matched laboratory measures of production characteristics) and the extent to which the ratings were gradual (i.e., they used the entire rating scales, rather than just the endpoints).

MAIN CONTRIBUTION

There were no consistent differences between non-SLPs/SLTs, less-experienced SLPs/SLTs and more-experienced SLPs/SLTs in a measure of the accuracy of responses. More consistent differences were found in the extent to which listeners used the endpoints of the scale: greater experience was associated with greater use of the endpoint values.

CONCLUSIONS & IMPLICATIONS

More-experienced SLPs/SLTs are less likely to use the entire range of continuous rating scales to rate children's speech accuracy than less-experienced SLPs/SLTs or clinically untrained listeners. Implications for service delivery are discussed. What this paper adds What is already known on the subject Children's productions of individual sounds, like /k/, become gradually more adult-like over the course of development. For a child who has a [t] for /k/ error, this gradual development means that children's productions become progressively less like /t/ and more like /k/ over development. Phonetic transcription does not capture this gradual development. In contrast, studies have shown that continuous ratings of children's speech (such as rating productions on a scale anchored by the text "the 't' sound" at one end and "the 'k' sound" at the other end) can capture this gradual development. What this paper adds to existing knowledge To determine continuous ratings are clinically feasible, we must first determine whether clinical experience affects people's use of continuous rating scales to rate children's speech. We conducted an on-line speech perception experiment in which 81 speech-language pathologists/speech and language therapists (SLPs/SLTs) and 20 non-SLPs/SLTs rated 60 productions by children on continuous rating scales. The 60 stimuli included many sounds that had been independently verified to be intermediate productions (i.e., a target /k/ that was neither completely /k/-like nor completely /t/-like). Non-SLPs/SLTs and less-experienced SLPs/SLTs rated those intermediate sounds with intermediate ratings (i.e., somewhere on the midpoint of a continuous scale). In contrast, more-experienced SLPs/SLTs were more likely to rate those sounds as instances of endpoints (i.e., as either /k/ or /t/). What are the potential or actual clinical implications of this work? This finding suggests that clinical experience is paradoxically associated with a reduced tendency to use the entire range of responses on continuous rating scales. This finding suggests that we must better understand the cause of this reduced tendency, so that clinicians at all levels can use continuous rating scales equally effectively.

What accounts for individual differences in susceptibility to the McGurk effect?

The McGurk effect is a classic audiovisual speech illusion in which discrepant auditory and visual syllables can lead to a fused percept (e.g., an auditory /bɑ/ paired with a visual /gɑ/ often leads to the perception of /dɑ/). The McGurk effect is robust and easily replicated in pooled group data, but there is tremendous variability in the extent to which individual participants are susceptible to it. In some studies, the rate at which individuals report fusion responses ranges from 0% to 100%. Despite its widespread use in the audiovisual speech perception literature, the roots of the wide variability in McGurk susceptibility are largely unknown. This study evaluated whether several perceptual and cognitive traits are related to McGurk susceptibility through correlational analyses and mixed effects modeling. We found that an individual's susceptibility to the McGurk effect was related to their ability to extract place of articulation information from the visual signal (i.e., a more fine-grained analysis of lipreading ability), but not to scores on tasks measuring attentional control, processing speed, working memory capacity, or auditory perceptual gradiency. These results provide support for the claim that a small amount of the variability in susceptibility to the McGurk effect is attributable to lipreading skill. In contrast, cognitive and perceptual abilities that are commonly used predictors in individual differences studies do not appear to underlie susceptibility to the McGurk effect.

The Roles of Vowel Fronting, Lengthening, and Listener Variables in the Perception of Vocal Femininity

PURPOSE

The goal of this study was to test whether fronting and lengthening of lax vowels influence the perception of femininity in listeners whose dialect is characterized as already having relatively fronted and long lax vowels in male and female speech.

METHOD

Sixteen English words containing the /ɪ ɛ ʊ ɑ/ vowels were produced by a male speaker with 2 degrees of vowel fronting. Then, the vowel duration was manipulated in 3 steps. Thirty-nine listeners from the Southern United States judged how feminine each word sounded to them on an interval scale.

RESULTS

The results of mixed-effects modeling showed that the words with more fronted and longer variants of the vowels were perceived as more feminine than the same words with less fronted and shorter variants of the vowels. These effects, however, were modulated by the vowel type, listener's area of upbringing, and gender.

CONCLUSIONS

Fronting (except for /ʊ/) and lengthening of lax vowels make words sound more feminine for Southern listeners, which has implications for clients who wish to modify the perception of femininity invoked by their speech. The relative strength of the gender and regional associations of these vowel characteristics should be further examined across dialects.