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The current study investigated whether phonetic complexity affected stuttering rate for Spanish speakers. The speakers were assigned to three age groups (6-11, 12-17 and 18 years plus) that were similar to those used in an earlier study on English. The analysis was performed using Jakielski's (1998) Index of Phonetic Complexity (IPC) scheme in which each word is given an IPC score based on the number of complex attributes it includes for each of eight factors. Stuttering on function words for Spanish did not correlate with IPC score for any age group. This mirrors the finding for English that stuttering on these words is not affected by phonetic complexity. The IPC scores of content words correlated positively with stuttering rate for 6-11 year old and adult speakers. Comparison was made between the languages to establish whether or not experience with the factors determines the problem they pose for speakers (revealed by differences in stuttering rate). Evidence was obtained that four factors found to be important determinants of stuttering on content words in English for speakers aged 12 and above, also affected Spanish speakers. This occurred despite large differences in frequency of usage of these factors. It is concluded that phonetic factors affect stuttering rate irrespective of a speaker's experience with that factor.

Previous work has shown that phonetic difficulty affects older, but not younger, speakers who stutter and that older speakers experience more difficulty on content words than function words. The relationship between stuttering rate and a recently-developed index of phonetic complexity (IPC, Jakielski, 1998) was examined in this study separately for function and content words for speakers in 6-11, 11 plus-18 and 18 plus age groups. The hypothesis that stuttering rate on the content words of older speakers, but not younger speakers, would be related to the IPC score was supported. It is argued that the similarity between results using the IPC scores with a previous analysis that looked at late emerging consonants, consonant strings and multiple syllables (also conducted on function and content words separately), validates the former instrument. In further analyses, the factors that are most likely to lead to stuttering in English and their order of importance were established. The order found was consonant by manner, consonant by place, word length and contiguous consonant clusters. As the effects of phonetic difficulty are evident in teenage and adulthood, at least some of the factors may have an acquired influence on stuttering (rather than an innate universal basis, as the theory behind Jakielski's work suggests). This may be established in future work by doing cross-linguistic comparisons to see which factors operate universally. Disfluency on function words in early childhood appears to be responsive to factors other than phonetic complexity.

Children aged between two and 10 years were assessed on a new reception of syntax test (ROST). Validations of the test are reported for monolingual ‘ uent control children under five (by examining the relationship with mean length of utterance and the Oxford Communication Development Inventory) and for over fives (relationship with a new judgement of grammaticality test using syntactic categories common to the two tests). Performance of these children was compared with performance of children who stutter and children with English as an additional language. In this study, the test was divided into under-five and over-five forms. Any young child progressing to the over-five syntactic categories, or any older child doing the under-five syntactic categories was dropped from the analysis. ROST scores prepared according to this scheme led to no differences between the control and either of the subject groups tested. However, compared to controls, the children with English as an additional language (but not children who stutter) had a significantly higher proportion of children above five who did the under-five categories (and were, therefore, excluded from the analyses). The higher proportion of children who did the under-five syntactic categories in the English as an additional language group indicates that group scores would have been lower if their syntax results had been included in the analysis. Further analyses provided some evidence that two groups with English as an additional language (Turkish and Cantonese speakers) did not perform any better on selected syntactic categories in their native language compared with their performance in English.

A recent study by Packman, Onslow, Coombes and Goodwin (2001) employed a non-word-reading paradigm to test the contribution of the lexical retrieval process to stuttering. They consider that, with this material, the lexical retrieval process could not contribute to stuttering and that either anxiety and/or the motor demand of reading are the governing factors. This paper will discuss possible processes underlying non-word reading and it argues that the conclusion arrived at by Packman et al. does not stand up to close scrutiny. In their introduction, the authors acknowledge that the lexicalization process involves retrieval and encoding of words. In a non-word-reading task, the word retrieval component is eliminated. The possibility that the encoding component of the lexicalization process leads to stuttering is, however, completely ignored by the authors when they attribute stuttering to motor demands. As theories put forward by Postma and Kolk (the Covert Repair Hypothesis, 1993) and Howell and Au-Yeung (the EXPLAN theory, 2002) argue heavily for the role of the phonological encoding processes in stuttering, Packman et al.'s work does not evaluate such theories. Theoretical issues aside, Packman et al.'s arguments about reading rate and stuttering rate based on reading time is also questionable.

Prins, Main, and Wampler (1997) examined whether people who stutter have slower lexical access time than people who do not stutter. Their study was based on the two-stage model of lexical access proposed by Kempen and Huijbers (1983). According to Kempen and Huijbers' model, lexicalization time (Lex) is divided into two separate non-overlapping stages: L1, lexicalization for retrieving semantic and syntactic information and L2, lexicalization for accessing the word form (articulatory plan). A picture-naming experiment was used to test the validity of their model. Kempen and Huijbers showed that the speech-onset time in naming an actor (a noun) was shorter than that in naming an action (a verb). This is shown in sections (a) and (b) of Figure 1 by the length of the lines along the time axis (the abscissa). The time to speech onset when naming both the actor and the action (noun plus verb), shown in Figure 1(c), was longer than that for naming just the actor. This showed that lexical access for the verb commenced before speech onset of the noun plus verb (N+V) utterance. The speech-onset time in naming both the actor and the action was, however, found to be approximately equal to that for naming just the action. Kempen and Huijbers argued that the L1 lexicalization time for both the noun and the verb overlapped, and the speech-onset time was dominated by the longer of the two, the L1 lexicalization time for the verb. This is shown in the L1-labelled sections on the left of Figure 1(c). When naming both the actor and the action, L2 lexicalization of the noun needs to be completed before speech onset. L2 lexicalization of the verb is assumed to occur in sequence after the L2 lexicalization of the noun, in parallel with the motor execution of the noun.

Two important determinants of variation in stuttering frequency are utterance rate and the linguistic properties of the words being spoken. Little is known how these determinants interrelate. It is hypothesized that those linguistic factors that lead to change in word duration, alter utterance rate locally within an utterance that then gives rise to an increase in stuttering frequency. According to the hypothesis, utterance rate variation should occur locally within the linguistic segments in an utterance that is known to increase the likelihood of stuttering. The hypothesis is tested using length of tone unit as the linguistic factor. Three predictions are confirmed: Utterance rate varies locally within the tone units and this local variation affects stuttering frequency; stuttering frequency is positively related to the length of tone units; variations in utterance rate are correlated with tone unit length. Alternative theoretical formulations of these findings are considered.

Stuttering on function words was examined in 51 people who stutter. The people who stutter were subdivided into young (2 to 6 years), middle (6 to 9 years), and older (9 to 12 years) child groups; teenagers (13 to 18 years); and adults (20 to 40 years). As reported by previous researchers, children up to about age 9 stuttered more on function words (pronouns, articles, prepositions, conjunctions, auxiliary verbs), whereas older people tended to stutter more on content words (nouns, main verbs, adverbs, adjectives). Function words in early positions in utterances, again as reported elsewhere, were more likely to be stuttered than function words at later positions in an utterance. This was most apparent for the younger groups of speakers. For the remaining analyses, utterances were segmented into phonological words on the basis of Selkirk’s work (1984). Stuttering rate was higher when function words occurred in early phonological word positions than other phonological word positions whether the phonological word appeared in initial position in an utterance or not. Stuttering rate was highly dependent on whether the function word occurred before or after the single content word allowed in Selkirk’s (1984) phonological words. This applied, once again, whether the phonological word was utterance-initial or not. It is argued that stuttering of function words before their content word in phonological words in young speakers is used as a delaying tactic when the forthcoming content word is not prepared for articulation.

Research on stuttering has concentrated on explaining dysfluencies by factors that are inherent to words, such as their semantic content or phonological characteristics. This has allowed speech to be analysed irrespective of the context in which it occurs. Research on fluent speakers has shown that conversational context affects whether speech is produced fluently or not. These studies have shown that the lexical items and syntactic structures (that other speakers engaged in conversation use) influence the fluency of speakers. In addition, fluent speech is disrupted when planning for forthcoming words and syntactic structures is taking place. In this article it is argued that such word-external factors could potentially also be triggers which lead to words being stuttered.

When asked to read a text, people who stutter produce dysfluencies that can be divided into two types. These are (a) those dysfluencies that mainly influence production of individual lexical items and (b) those involving, either alone or in combination, omitting words, inserting incorrect words and repeating phrases. In case (a), the speech breakdowns are termed lexical dysfluencies (LD). LD include word and part-word repetitions, prolongations, and broken words. The dysfluencies in (b) are termed supralexical (SD). This class comprises interjections, revisions, incomplete phrases, and phrase repetitions. If SD and LD are not distinguished, then the way certain dysfluent words should be categorized is inherently ambiguous. For instance, there is no a priori way of deciding how to categorize an LD that occurs within a group of words comprising an SD. The proposed solution to this problem involves locating and processing SD before LD. Doing this allows any LD that occurs within a group of words that can also be designated as an SD to be assessed and removed from further consideration prior to location of isolated LD (the LD that occur within an SD are, then, subordinate to the SD). A computer-based parser that locates SD in transcriptions of read text is described. Its performance is compared with that of human judges.

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.

Though the phonological difficulty of a word might reasonably be supposed to influence whether a word is stuttered, it has recently been reported that the incidence of stuttering does not depend on this factor in child stutterers. This conclusion is reexamined in the current report. Data are employed that were obtained from groups of child stutterers (and their controls) who vary in age and severity of their disorder. First, it is shown that the measure of phonological difficulty reveals differences in phonological ability for children of different ages (stutterers and fluent controls). The properties of words with regard to whether they are function words or content words, their position in the sentence, their length, and the phoneme that they start with vary between phonological categories (referred to as “Brown's factors”). Since these factors could influence whether words are stuttered in their own right, they may led to apparent differences in stuttering between words in different phonological categories that are spurious. Alternatively, these factors may disguise influences that phonological categories have on stuttering. It is shown in the next analysis that the words in the various phonological categories differ with regard to Brown's factors. In the final analysis, the proportion of words stuttered for words in each phonological category are analyzed so that any influence Brown's factors might have are removed by treating the factors as covariates. No dependence of stuttering on phonological category is observed for age group, stutterer's severity, or word types (stuttered word or word following the stuttered word). Thus, phonological difficulty as measured here and elsewhere does not appear to be a major factor governing the incidence of stuttering in children.

Recent research into stuttering in English has shown that function word disfluency decreases with age whereas content words disfluency increases. Also function words that precede a content word are significantly more likely to be stuttered than those that follow content words (Au-Yeung, Howell and Pilgrim, 1998; Howell, Au-Yeung and Sackin, 1999). These studies have used the concept of the phonological word as a means of investigating these phenomena. Phonological words help to determine the position of function words relative to content words and to establish the origin of the patterns of disfluency with respect to these two word classes. The current investigation analysed German speech for similar patterns. German contains many long compound nouns; on this basis, German content words are more complex than English ones. Thus, the patterns of disfluency within phonological words may differ between German and English. Results indicated three main findings. Function words that occupy an early position in a PW have higher rates of disfluency than those that occur later in a PW, this being most apparent for the youngest speakers. Second, function words that precede the content word in a PW have higher rates of disfluency than those that follow the content word. Third, young speakers exhibit high rates of disfluency on function words, but this drops off with age and, correspondingly, disfluency rate on content words increases. The patterns within phonological words may be general to German and English and can be accounted for by the EXPLAN model, assuming lexical class operates equivalently across these languages or that lexical categories contain some common characteristic that is associated with fluency across the languages.

This study investigated whether frequency of stuttering was affected by factors that specify the phonological difficulty of a sound and whether and how any influences vary across age groups. Analyses were performed separately on content words and function words. The phonological factors examined were: a) Whether the word contained a late emerging consonant (LEC); and b) Whether the word contained a consonant string (CS). Analyses showed that these factors occurred at different rates across the age groups used (children under 12, teenagers between 12 and 18, and adults). A more detailed breakdown was also reported of frequency of usage of LEC and CS over age groups depending on whether and where these factors occurred in the content words; all nine combinations of no LEC, word-initial LEC, non-initial LEC with no CS, word-initial CS, and non-initial CS were examined. Usage of certain of these nine categories varied over age groups. Friedman statistic on the ratio of stuttering (proportion of stuttered words in a particular word class divided by the proportion of words in that particular word class) showed that the frequency of stuttering remained high for adult speakers when CS and LEC both occurred in a word and when they appeared in word-initial position. These findings support a recently proposed theory that accounts for life-span changes in stuttering.

The main purpose of the present study was to examine whether the developmental change in loci of disfluency from mainly function words to mainly content words, observed for English speakers who stutter (P. Howell, J. Au-Yeung, & S. Sackin, 1999), also occurs for comparable Spanish speakers who stutter. The participants were divided into 5 age groups. There were 7 participants in Group 1, from 3 to 5 years old; 11 in Group 2, from 6 to 9 years old; 10 in Group 3, from 10 to 11 years old; 9 in Group 4, from 12 to 16 years old; and 9 in Group 5, from 20 to 68 years old. Across all groups, 36 of the 46 participants were male. The study method involved segmenting speech into phonological words (PWs) that consist of an obligatory content word with optional function words that precede and follow it. The initial function words in the PWs were examined to establish whether they have a higher disfluency rate than the final ones (J. Au-Yeung, P. Howell, & L. Pilgrim, 1998). Disfluency on function words in a PW was higher when the word occurred before a content word rather than after a content word for all age groups. Disfluencies on function and content words were then examined to determine whether they change over age groups in the same way as for English speakers who stutter (Howell et al., 1999). The rate of disfluency on function words was higher than that on content words, particularly in the youngest speakers. Function word disfluency rate dropped off and content word disfluency rate increased across age groups. These patterns are similar to those reported for English. Possible explanations for these similarities across the two languages are discussed.

Dysfluencies on function words in the speech of people who stutter mainly occur when function words precede, rather than follow, content words (Au-Yeung, Howell, & Pilgrim, 1998). It is hypothesized that such function word dysfluencies occur when the plan for the subsequent content word is not ready for execution. Repetition and hesitation on the function words buys time to complete the plan for the content word. Stuttering arises when speakers abandon the use of this delaying strategy and carry on, attempting production of the subsequent, partly prepared content word. To test these hypotheses, the relationship between dysfluency on function and content words was investigated in the spontaneous speech of 51 people who stutter and 68 people who do not stutter. These participants were subdivided into the following age groups: 2–6-year-olds, 7–9-year-olds, 10–12-year-olds, teenagers (13–18 years), and adults (20–40 years). Very few dysfluencies occurred for either fluency group on function words that occupied a position after a content word. For both fluency groups, dysfluency within each phonological word occurred predominantly on either the function word preceding the content word or on the content word itself, but not both. Fluent speakers had a higher percentage of dysfluency on initial function words than content words. Whether dysfluency occurred on initial function words or content words changed over age groups for speakers who stutter. For the 2–6-year-old speakers that stutter, there was a higher percentage of dysfluencies on initial function words than content words. In subsequent age groups, dysfluency decreased on function words and increased on content words. These data are interpreted as suggesting that fluent speakers use repetition of function words to delay production of the subsequent content words, whereas people who stutter carry on and attempt a content word on the basis of an incomplete plan.