Acoustic consequences of articulatory variability during productions of /t/ and /k/ and its implications for speech error research

A perception-induced /t/-to-/k/ sound change: evidence from a cross-linguistic study

John Ohala claimed that the source of sound change may lie in misperceptions which can be replicated in the laboratory. We tested this claim for a historical change of /t/ to /k/ in the coda in the Southern Min dialect of Chaoshan. We conducted a forced-choice segment identification task with CVC syllables in which the final C varied across the segments [p t k ʔ] in addition to a number of further variables, including the V, which ranged across [i u a]. The results from three groups of participants whose native languages have the coda systems /p t k ʔ/ (Zhangquan), /p k ʔ/ (Chaoshan) and /p t k/ (Dutch) indicate that [t] is the least stably perceived segment overall. It is particularly disfavoured when it follows [a], where there is a bias towards [k]. We argue that this finding supports a perceptual account of the historically documented scenario whereby a change from /at/ to /ak/ preceded and triggered a more general merger of /t/ with /k/ in the coda of Chaoshan. While we grant that perceptual sound changes are not the only or even the most common type of sound change, the fact that the perception results are essentially the same across the three language groups lends credibility to Ohala's perceptually motivated sound changes.

Using Mahalanobis Distances to Investigate Second Dialect Acquisition: A Study on Quebec French

Second dialect acquisition (SDA) can be defined as the process through which geographically mobile individuals adapt to new dialect features of their first language. Two common methodological approaches in SDA studies could lead to underestimating the phonetic changes that mobile speakers may experience: only large phonetic differences between dialects are considered, and external sources are used to infer what should have been the speakers' original dialect. By contrast, in this study, we carry out a longitudinal analysis to empirically assess the speakers' baseline and shift away from it with no priors as to which features should change or not. Furthermore, we focus on Quebec French, a variety with a relatively crowded vowel space. Using Mahalanobis distances, we measure how acoustic characteristics of vowels produced by 15 mobile speakers change relative to those of a control group of 8 sedentary speakers, with the mobile participants recorded right after they moved to Quebec City, then a year later. Overall, the results show a reduction of Mahalanobis distances over time, indicating convergence toward the control system. Convergence also tends to be greater in denser areas of the vowel space. These results suggest that phonetic changes during SDA could be finer than previously thought. This study calls for the use of methodological approaches that can reveal such trends, and contributes to uncovering the extent of phonetic flexibility during adulthood.

Investigating Perceptual Biases, Data Reliability, and Data Discovery in a Methodology for Collecting Speech Errors From Audio Recordings

This work describes a methodology of collecting speech errors from audio recordings and investigates how some of its assumptions affect data quality and composition. Speech errors of all types (sound, lexical, syntactic, etc.) were collected by eight data collectors from audio recordings of unscripted English speech. Analysis of these errors showed that: (i) different listeners find different errors in the same audio recordings, but (ii) the frequencies of error patterns are similar across listeners; (iii) errors collected "online" using on the spot observational techniques are more likely to be affected by perceptual biases than "offline" errors collected from audio recordings; and (iv) datasets built from audio recordings can be explored and extended in a number of ways that traditional corpus studies cannot be.

Phonological regularity, perceptual biases, and the role of phonotactics in speech error analysis

Speech errors involving manipulations of sounds tend to be phonologically regular in the sense that they obey the phonotactic rules of well-formed words. We review the empirical evidence for phonological regularity in prior research, including both categorical assessments of words and regularity at the granular level involving specific segments and contexts. Since the reporting of regularity is affected by human perceptual biases, we also document this regularity in a new data set of 2,228 sublexical errors that was collected using methods that are demonstrably less prone to bias. These facts validate the claim that sound errors are overwhelmingly regular, but the new evidence suggests speech errors admit more phonologically ill-formed words than previously thought. Detailed facts of the phonological structure of errors, including this revised standard, are then related to model assumptions in contemporary theories of phonological encoding. This article is categorized under: Linguistics > Linguistic Theory Linguistics > Computational Models of Language Psychology > Language.

The difficulty of articulatory complexity

In our commentary, we offer some support for the view that frequency rather than a language-independent definition of complexity is a main factor determining speech production in healthy adults. We further discuss the limits of defining articulatory complexity based on transcription data. If we want to gauge the impact of substantive constraints on speech production, context-specific production dynamics should be considered, as has been underscored by articulatory-acoustic work on speech errors.

Temporal control in the voicing contrast: Evidence from surgery-related apraxia of speech

The goal of this study was to investigate the phonetic realisation of the voicing feature in two tumour resection-related Spanish speakers with apraxia of speech. Temporal parameters related to the phonological contrast of voicing in Spanish have been analysed for intervocalic voiced and voiceless obstruents embedded in isolated words and nonwords, and compared with data collected from healthy speakers. Results indicate that in devoiced productions, where VOT values fitted the 'voiceless stops' category, vowel duration values matched those of voiced stops and suggested the preservation of contextual voicing cues. An attempt at preserving a consonant/vowel duration ratio consistent with aerodynamic predictions for voicing contrast has been observed in apraxic correct production as well as in devoicing errors, but not in the control group, which could be interpreted as a compensatory mechanism.

The Effect of Auditory Information on Patterns of Intrusions and Reductions

PURPOSE

The study investigates whether auditory information affects the nature of intrusion and reduction errors in reiterated speech. These errors are hypothesized to arise as a consequence of autonomous mechanisms to stabilize movement coordination. The specific question addressed is whether this process is affected by auditory information so that it will influence the occurrence of intrusions and reductions.

METHODS

Fifteen speakers produced word pairs with alternating onset consonants and identical rhymes repetitively at a normal and fast speaking rate, in masked and unmasked speech. Movement ranges of the tongue tip, tongue dorsum, and lower lip during onset consonants were retrieved from kinematic data collected with electromagnetic articulography. Reductions and intrusions were defined as statistical outliers from movement range distributions of target and nontarget articulators, respectively.

RESULTS

Regardless of masking condition, the number of intrusions and reductions increased during the course of a trial, suggesting movement stabilization. However, compared with unmasked speech, speakers made fewer intrusions in masked speech. The number of reductions was not significantly affected.

CONCLUSIONS

Masking of auditory information resulted in fewer intrusions, suggesting that speakers were able to pay closer attention to their articulatory movements. This highlights a possible stabilizing role for proprioceptive information in speech movement coordination.

Acoustic and perceptual evaluation of category goodness of /t/ and /k/ in typical and misarticulated children's speech

This investigation explores perceptual and acoustic characteristics of children's successful and unsuccessful productions of /t/ and /k/, with a specific aim of exploring perceptual sensitivity to phonetic detail, and the extent to which this sensitivity is reflected in the acoustic domain. Recordings were collected from 4- to 8-year-old children with a speech sound disorder (SSD) who misarticulated one of the target plosives, and compared to productions recorded from peers with typical speech development (TD). Perceptual responses were registered with regards to a visual-analog scale, ranging from "clear [t]" to "clear [k]." Statistical models of prototypical productions were built, based on spectral moments and discrete cosine transform features, and used in the scoring of SSD productions. In the perceptual evaluation, "clear substitutions" were rated as less prototypical than correct productions. Moreover, target-appropriate productions of /t/ and /k/ produced by children with SSD were rated as less prototypical than those produced by TD peers. The acoustical modeling could to a large extent discriminate between the gross categories /t/ and /k/, and scored the SSD utterances on a continuous scale that was largely consistent with the category of production. However, none of the methods exhibited the same sensitivity to phonetic detail as the human listeners.

Voice onset time in consonant cluster errors: can phonetic accommodation differentiate cognitive from motor errors?

PURPOSE

Phonetic accommodation in speech errors has traditionally been used to identify the processing level at which an error has occurred. Recent studies have challenged the view that noncanonical productions may solely be due to phonetic, not phonological, processing irregularities, as previously assumed. The authors of the present study investigated the relationship between phonological and phonetic planning processes on the basis of voice onset time (VOT) behavior in consonant cluster errors.

METHOD

Acoustic data from 22 German speakers were recorded while eliciting errors on sibilant-stop clusters. Analyses consider VOT duration as well as intensity and spectral properties of the sibilant.

RESULTS

Of all incorrect responses, 28% failed to show accommodation. Sibilant intensity and spectral properties differed from correct responses irrespective of whether VOT was accommodated.

CONCLUSIONS

The data overall do not allow using (a lack of) accommodation as a diagnostic as to the processing level at which an error has occurred. The data support speech production models that allow for an integrated view of phonological and phonetic processing.

The relationship between the perception and production of coarticulation during a sound change in progress

The present study is concerned with lax /u/-fronting in Standard British English and in particular with whether this sound change in progress can be attributed to a waning of the perceptual compensation for the coarticulatory effects of context. Younger and older speakers produced various monosyllables in which /u/ occurred in different symmetrical consonantal contexts. The same speakers participated in a forced-choice perception experiment in which they categorized a synthetic /I-u/ continuum embedded in fronting /s_t/ and non-fronting /w_l/ contexts. /u/ was shown to be fronted for the younger age group in both production and perception. Although there was no conclusive evidence that younger listeners compensated less for coarticulation than did older listeners, the size of the coarticulatory influence of consonantal context on /u/ in perception was found to be smaller than in production for the younger than for the older group. The findings are consistent with a model of sound change in which the perceptual compensation for coarticulation wanes ahead of changes that take place to coarticulatory relationships in speech production. As a result, the perception and production of coarticulation may be unusually misaligned with respect to each other for some speaker-listeners participating in a sound change in progress.