Phonotactic cues for segmentation of fluent speech by infants

There is growing evidence that infants become sensitive to the probabilistic phonotactics of their ambient language sometime during the second half of their first year. The present study investigates whether 9-month-olds make use of phonotactic cues to segment words from fluent speech. Using the Headturn Preference Procedure, we found that infants listened to a CVC stimulus longer when the stimulus previously appeared in a sentential context with good phonotactic cues than when it appeared in one without such cues. The goodness of the phonotactic cues was estimated from the frequency with which the C.C clusters at the onset and offset of a CVC test stimulus (i.e. C.CVC.C) are found within and between words in child-directed speech, with high between-word probability associated with good cues to word boundaries. A similar segmentation result emerged when good phonotactic cues occurred only at the onset (i.e. C.CVC.C) or the offset (i.e. C.CVC.C) of the target words in the utterances. Together, the results suggest that 9-month-olds use probabilistic phonotactics to segment speech into words and that high-probability between-word clusters are interpreted as both word onsets and word offsets.     

Twenty-two-month-olds discriminate fluent from disfluent adult-directed speech

Deviation of real speech from grammatical ideals due to disfluency and other speech errors presents potentially serious problems for the language learner. While infants may initially benefit from attending primarily or solely to infant-directed speech, which contains few grammatical errors, older infants may listen more to adult-directed speech. In a first experiment, Post-verbal infants preferred fluent speech to disfluent speech, while Pre-verbal infants showed no preference. In a second experiment, Post-verbal infants discriminated disfluent and fluent speech even when lexical information was removed, showing that they make use of prosodic properties of the speech stream to detect disfluency. Because disfluencies are highly correlated with grammatical errors, this sensitivity provides infants with a means of filtering ungrammaticality from their input.     

Effects of target monitoring on understanding fluent speech

Phoneme monitoring and word monitoring are two experimental tasks that have frequently been used to assess the processing of fluent speech. Each task is purported to provide an “online” measure of the comprehension process, and each requires listeners to pay conscious attention to some aspect or property of the sound structure of the speech signal. The present study is primarily a methodological one directed at the following question: Does the allocation of processing resources for conscious analysis of the sound structure of the speech signal affect ongoing comprehension processes or the ultimate level of understanding achieved for the content of the linguistic message? Our subjects listened to spoken stories. Then, to measure their comprehension, they answered multiple-choice questions about each story. During some stories, they were required to detect a specific phoneme; during other stories, they were required to detect a specific word; during still other stories, they were not required to monitor the utterance for any target. The monitoring results replicated earlier findings showing longer detection latencies for phoneme monitoring than for word monitoring. Somewhat surprisingly, the ancillary phoneme- and word-monitoring tasks did not adversely affect overall comprehension performance. This result undermines the specific criticism that on-line monitoring paradigms of this kind should not be used to study spoken language understanding because these tasks interfere with normal comprehension.     

Infant perception of audio-visual speech synchrony in familiar and unfamiliar fluent speech

We investigated the effects of linguistic experience and language familiarity on the perception of audio-visual (A-V) synchrony in fluent speech. In Experiment 1, we tested a group of monolingual Spanish- and Catalan-learning 8-month-old infants to a video clip of a person speaking Spanish. Following habituation to the audiovisually synchronous video, infants saw and heard desynchronized clips of the same video where the audio stream now preceded the video stream by 366, 500, or 666 ms. In Experiment 2, monolingual Catalan and Spanish infants were tested with a video clip of a person speaking English. Results indicated that in both experiments, infants detected a 666 and a 500 ms asynchrony. That is, their responsiveness to A-V synchrony was the same regardless of their specific linguistic experience or familiarity with the tested language. Compared to previous results from infant studies with isolated audiovisual syllables, these results show that infants are more sensitive to A-V temporal relations inherent in fluent speech. Furthermore, the absence of a language familiarity effect on the detection of A-V speech asynchrony at eight months of age is consistent with the broad perceptual tuning usually observed in infant response to linguistic input at this age.     

Acoustic evidence of aberrant velocities in stutterers' fluent speech

Movement rates of formant frequencies and the extents of articulatory change were spectrographically analyzed in the fLuent (VCV) utterances of 20 stutterers and nonstutterers. The velocities of articulator movement throughout the first vowel and velocities into the second vowel were not significantly different for the two groups. These mean rates of movement, although nonsignificant, were slower in stutterers and slightly more variable, and the extent of articulator movement was comparable. These results do not support the contentions that stutterers use coarticulatory movements that are too rapid or that stutterers have a poorer competence for rapid coordination of speech movements. The rationales of rate-control treatment methods to slow coarticulatory movements in stutterers need to be reexamined.     

Perceptual comparisons of adolescent stutterers' and nonstutterers' fluent speech

Numerous investigators have reported that listeners are able to perceptually differentiate adult stutterers' and nonstutterers' fluent speech productions. However, findings from similar studies with children ranging in age from 3 to 9 yr have indicated that perceptual discrimination of child stutterers is difficult. A logical extension of this line of investigation would be to determine when during maturation from childhood to adulthood stutterers' fluent speech becomes perceptibly different than nonstutterers'. Therefore, in this study similar fluent speech samples from seven 12–16-yr-old adolescent male stutterers and seven matched nonstutterers were analyzed perceptually in a paired stimulus paradigm by 15 sophisticated listeners. Individual subject analyses using signal detection theory revealed that five of the seven stutterers were discriminated. When averaged for subject group comparison, these findings indicated that listeners successfully discriminated between the fluent speech of the two groups. Therefore, the perceptual difference in fluent speech production reported previously for adults appears to be present by adolescence.     

Perceptual analyses of stuttering and nonstuttering children's fluent speech productions

Several investigators have reported a significant perceptual difference between adult stutterers' and nonstutterers' fluent speech productions. However, there is only limited information concerning the perceptual evaluation of stuttering and nonstuttering children's fluent speech. Therefore, in this study identical fluent sentences from nine stuttering children (mean age = 6 yrs, 8 mos) and nine nonstuttering children matched individually for sex and age (within 6 mos) were analyzed perceptually in both a paired- and single-stimulus paradigm by 12 sophisticated listeners. Individual subject analyses revealed that only one-half or fewer of the stutterers could be discerned in either paradigm. In the remaining cases, either no discrimination could be made or a nonstutterer was incorrectly identified as a stutterer. When averaged for subject group comparison, these findings indicated that listeners could not discriminate between the two groups. Possible explanations for this discrepancy in results between child and adult stutterers are proposed.     

Temporal characteristics in the fluent speech of child stutterers and nonstutterers

Past research reveals that adult stutterers often possess aberrant speech-timing abilities. As yet, only Healey and Adams (1981) have investigated these abilities in child stutterers. The present study attempted to assess the speech-timing skills of child stutterers and normal-speaking children while performing both simple and complex speech. Each subject was required to participate in two tasks: a sentence repetition task for simple speech and a story-retelling task for complex speech. Results supported those found by Healey and Adams, indicating that child stutterers have speech-timing abilities similar to normal-speaking children in simple speech tasks. The complex task, however, revealed that stutterers exhibited more frequent and longer interword pauses than nonstutterers. Two hypotheses generated from past research are offered to explain these differences. A third untested theory is also presented.     

Formant transitions in the fluent speech of Farsi-speaking people who stutter

PurposeSecond formant (F2) transitions can be used to infer attributes of articulatory transitions. This study compared formant transitions during fluent speech segments of Farsi (Persian) speaking people who stutter and normally fluent Farsi speakers.MethodsTen Iranian males who stutter and 10 normally fluent Iranian males participated. Sixteen different “CVt” tokens were embedded within the phrase “Begu CVt an”. Measures included overall F2 transition frequency extents, durations, and derived overall slopes, initial F2 transition slopes at 30 ms and 60 ms, and speaking rate.Results(1) Mean overall formant frequency extent was significantly greater in 14 of the 16 CVt tokens for the group of stuttering speakers. (2) Stuttering speakers exhibited significantly longer overall F2 transitions for all 16 tokens compared to the nonstuttering speakers. (3) The overall F2 slopes were similar between the two groups. (4) The stuttering speakers exhibited significantly greater initial F2 transition slopes (positive or negative) for five of the 16 tokens at 30 ms and six of the 16 tokens at 60 ms. (5) The stuttering group produced a slower syllable rate than the non-stuttering group.ConclusionsDuring perceptually fluent utterances, the stuttering speakers had greater F2 frequency extents during transitions, took longer to reach vowel steady state, exhibited some evidence of steeper slopes at the beginning of transitions, had overall similar F2 formant slopes, and had slower speaking rates compared to nonstuttering speakers. Findings support the notion of different speech motor timing strategies in stuttering speakers. Findings are likely to be independent of the language spoken.Educational objectives This study compares aspects of F2 formant transitions between 10 stuttering and 10 nonstuttering speakers. Readers will be able to describe: (a) characteristics of formant frequency as a specific acoustic feature used to infer speech movements in stuttering and nonstuttering speakers, (b) two methods of measuring second formant (F2) transitions: the visual criteria method and fixed time criteria method, (c) characteristics of F2 transitions in the fluent speech of stuttering speakers and how those characteristics appear to differ from normally fluent speakers, and (d) possible cross-linguistic effects on acoustic analyses of stuttering.     

An interaction between prosody and statistics in the segmentation of fluent speech

Sensitivity to prosodic cues might be used to constrain lexical search. Indeed, the prosodic organization of speech is such that words are invariably aligned with phrasal prosodic edges, providing a cue to segmentation. In this paper we devise an experimental paradigm that allows us to investigate the interaction between statistical and prosodic cues to extract words from a speech stream. We provide evidence that statistics over the syllables are computed independently of prosody. However, we also show that trisyllabic sequences with high transition probabilities that straddle two prosodic constituents appear not to be recognized. Taken together, our findings suggest that prosody acts as a filter, suppressing possible word-like sequences that span prosodic constituents.     

A model of serial order problems in fluent, stuttered and agrammatic speech

Many models of speech production have attempted to explain dysfluent speech. Most models assume that the disruptions that occur when speech is dysfluent arise because the speakers make errors while planning an utterance. In this contribution, a model of the serial order of speech is described that does not make this assumption. It involves the coordination or 'interlocking' of linguistic planning and execution stages at the language-speech interface. The model is examined to determine whether it can distinguish two forms of dysfluent speech (stuttered and agrammatic speech) that are characterized by iteration and omission of whole words and parts of words.     

Syntactic determinants of stuttering in the spontaneous speech of normally fluent and stuttering children

Conflicting findings have been reported concerning whether fluent children use more complex syntactic structures than stutterers and whether or not stutterers experience specific difficulty with complex syntactic structures. On critical examination, the first of these apparent discrepancies appears to be due to (a) differences in the methods employed for syntactic analysis in different studies, and (b) misleading impressions gained by looking at speakers within a single age range. Data were reanalyzed where one method of analysis had shown that fluent speakers and stutterers did not differ with regard to syntactic structures used but where they did show a propensity for stuttering to occur on complex syntactic structures. These data cover a range of age groups. When the second method of syntactic analysis was applied, a difference was found between fluent speakers and stutterers, with the stutterers initially using more simple structures and fewer complex ones. This difference decreased over age groups. However, a difference still remained with respect to which syntactic structures stutterers experience difficulty. An additional analysis, not formerly conducted on these data, showed that, as reported elsewhere, there was a higher probability of stuttering on clause-initial and. It was also shown that this tendency decreased with age group of the stutterers.     

Idiosyncratic effects of noncontingent reinforcement on problematic speech

Noncontingent reinforcement (NCR) was used to treat the attention‐maintained problematic speech of an adult male diagnosed with moderate mental retardation. A series of functional assessments was conducted that included informant interviews and a brief experimental analysis. A multiple‐baseline design was then used to assess the effects of NCR across two different therapists. Although the target behavior was substantially decreased from baseline levels, the reduction was inversely related to the density of the NCR schedule. Within‐session analyses were then used to hypothesize putative behavior‐change mechanisms responsible for the reduction. The results are discussed in relation to the active components underlying the effects of NCR. Copyright © 1999 John Wiley & Sons, Ltd.     

The treatment of stammering in children by the shadowing method

There are very few reports about the application of behaviour therapy to child stammering and these are not encouraging. Remedial education treatment is followed by frequent relapses. The present work gives data about the methods, effects and long-term results in nineteen child stammerers treated by the shadowing technique. A discussion of some of the theoretical problems involved is given and shows how the theoretical analysis influences treatment procedures. Seventy per cent of the cases were successfully treated by the shadowing technique and subsidiary procedures; relapses occurred in only 12 per cent of the cases.     

Effects of different attention tasks on concurrent speech in adults who stutter and fluent controls

Purpose: Motor theories indicate that focusing attention on well-practiced movements interferes with skilled performance; however, specific forms of attention (alerting vs. orienting vs. executive control) associated with this effect are not well understood. The present study explored this question in relation to stuttering, and examined whether dual task conditions that engaged sustained attention or working memory (WM) affected speech fluency in different ways. We also considered whether fluency changes were associated with changes in speech rate and language.Methods: Nineteen adults who stutter (AWS) and 20 controls produced spontaneous speech under a baseline condition and two dual task conditions: one involving a sustained attention task, the other involving WM demands.Results: Both groups produced fewer stutter-like disfluencies under dual task relative to baseline conditions and this reduction did not differ between the two dual tasks (attention vs. WM). Speech rate and language variables, which were potentially influenced by attention conditions, were not affected by dual tasks in the same way as disfluencies, and appeared to be unassociated with fluency results.Conclusions: Findings indicate that atypical disfluencies decrease when attention is divided, even when secondary task demands are minimal, as they were in the sustained attention task. For simple secondary tasks, fluency changes do not appear to be a byproduct of slowed rate and are not accompanied by observable changes in language. These results demonstrate that simple manipulations of attention can induce measurable effects on aspects of speech production, and may be a useful tool for facilitating fluency in clinical intervention.