Effects of Stuttering Frequency, Speaking Rate and Treatment on Speech Naturalness in Adults Who Stutter

Purpose: Individuals who stutter can often exhibit speech patterns that sound unnatural compared to individuals who do not stutter. Unnaturalness can be due to several underlying factors including the presence of stuttering itself and the unintended consequences of treatment approaches that alter speech motor patterns. Understanding factors that impact speech naturalness within the stuttering population can help improve the clinical management of the disorder. The current study investigates the relationship between pause duration, speech rate and stuttering frequency, and listener ratings of speech naturalness in a group of adults who stutter (AWS) before and after participation in a stuttering treatment program. Methods: Participants include 34 individuals who stutter, who were enrolled in a group-based, intensive, four-week fluency-shaping stuttering treatment program. One-minute audio video recordings were obtained from monologue speaking activities recorded prior to and following stuttering treatment. The audio track from each video sample was extracted and submitted to an acoustic analysis software to extract two measures. Pause duration was determined by identifying the temporal extent of all pauses greater than 250 ms. Fluent syllable rate was determined by measuring the overall duration and syllable count drawn from three perceptually fluent runs of speech in each video sample. These measures were combined with speech naturalness ratings and stuttering frequency data reported in previous studies conducted on this participant pool. Paired t-tests were used to assess pre vs. post-treatment differences in mean pause time, fluent syllable rate, mean naturalness ratings and stuttering frequency. Linear regression was used to identify associations between pause time, syllable rate, stuttering frequency, and speech naturalness. Effects of Stuttering Frequency, Speaking Rate and Treatment on Speech Naturalness 3 Results: Results revealed that following participation in stuttering treatment, the speech samples were rated as more natural, (t: 1.92; p=0.03), exhibited a dramatically reduced stuttering frequency (t: 10.18; p<0.00005), had significantly longer pause durations (t: -4.1145; p=.0001), and showed no change in fluent syllable rate. Linear regression results indicated that prior to treatment, stuttering frequency was the strongest predictor of speech naturalness, accounting for over 60 % of the variance in naturalness ratings. Pause duration and syllable rate provided little predictive value for pre-treatment speech naturalness ratings. Following treatment, pause duration was the strongest predictor of speech naturalness, accounting for more than 50 % of the variance in naturalness ratings. Syllable rate and stuttering frequency were not significantly associated with speech naturalness ratings. Conclusion: While there is a great deal of individual variation, speech samples of persons who stutter are commonly rated as unnatural sounding to listeners. This is true even after participating in some treatment programs designed to reduce or eliminate stuttering. Prior to treatment, stuttering frequency is the best predictor of speech naturalness. However, following treatment, stuttering frequency ceases to have predictive value. Instead, it was found that the duration of pausing between successive runs of speech is a much better predictor of speech naturalness following treatment. These two findings suggest that, within the same group of speakers, speech naturalness ratings are influenced by different kinds of factors. One interpretation is that following treatment, participants used longer speech pauses to plan the integration of the fluency enhancing speech targets. The result was relatively fluent, but still unnatural sounding speech. Results from the current study may provide future speech-language pathologists with Effects of Stuttering Frequency, Speaking Rate and Treatment on Speech Naturalness 4 information contributing to improved speech naturalness as an outcome of intervention in stuttering treatment programs. Effects of Stuttering Frequency, Speaking Rate and Treatment on Speech Naturalness 5 Chapter 1: Introduction What is Stuttering? Stuttering is a speech disorder that affects about one percent of the population. It is primarily characterized by intermittent disruptions of speech including sound, syllable and word repetitions, sound prolongations and hesitations or pauses in speech. These disruptions can have associated muscle tension and extraneous movements of the body. Stuttering typically begins in childhood between the ages of two and four years when speech and language skills are rapidly developing. While as many as 80 percent of children who begin to stutter will recover unassisted, for those who persist, stuttering will typically be a chronic, lifelong condition (Yairi and Ambrose, 2005). For those who chronically stutter, it is not uncommon to have additional characteristics including concomitant physical behaviors such as increased muscle tension, eye blinking, facial grimacing, avoidance of difficult words and speaking situations, the development of negative thoughts and emotions about speaking and other social situations. For many, social, emotional and cognitive factors may have a larger impact than primary stuttering behaviors. Emotional reactions seen in persons who stutter (PWS) can include fear, anxiety, feeling of being trapped, panic, embarrassment, shame, humiliation, anger and resentment (Yairi & Seery, 2015). Heightened emotional reactions are common in PWS and as a consequence, PWS commonly avoid engaging in typical activities of daily life and social interactions. Living with stuttering can also negatively influence thoughts and attitudes about speaking and communication as a whole. Attitudinal surveys in children and adults who stutter reveal significant negative attitudes about communication (Yairi & Seery, 2015). Because of the impact social, cognitive and emotional variables can have on PWS, it is important to take those variables into consideration during the treatment process of stuttering therapy. Effects of Stuttering Frequency, Speaking Rate and Treatment on Speech Naturalness 6 Approaches to Stuttering Treatment While there is a long history of research interest in developing pharmaceutical and technological treatments for stuttering, the most common approach to stuttering treatment involves a range of behavioral interventions. Most mainstream stuttering interventions focus on treating one or more of the following issues: reducing the severity of stuttering events, increasing speech fluency (i.e. reduce the frequency of stuttering), helping the client develop more positive thoughts and feelings about speaking and stuttering, and assisting the client in removing barriers to social interaction and ultimately improving the client’s quality of life. The first two of these issues address the primary stuttering behaviors. The first approach, commonly termed stuttering modification, involves teaching clients to systematically alter stuttering patterns to make them less disruptive to communication. The second term, commonly termed fluency-shaping, focuses on changing the whole manner of speaking rather than only the stuttering event. The main objective of fluency-shaping is to employ methods known to facilitate fluency and decrease stuttering. These methods can include stretching and slowing speech, altering speech rhythm, changing the manner of voice and consonant production, and increasing breath support for speech production. These new speaking patterns are practiced until fluency is obtained. Speech patterns are then adjusted slowly while still maintaining fluency to make the speech changes less noticeable to the speaker and client. These changes may be achieved simply through instruction and practice or can be facilitated using delayed auditory feedback (DAF), and forms of biofeedback (Yairi & Seery, 2015). Fluency-shaping treatment approaches, which is the focus of the current study, has a large research body supporting its use when the aim is to reducing stuttering frequency (Bothe et al. 2006). For example, the rhythmic speech approach which utilizes methods like finger tapping Effects of Stuttering Frequency, Speaking Rate and Treatment on Speech Naturalness 7 and using a metronome to keep rhythm when speaking, have been successful in significantly reducing stuttering frequency. A study done by Trajkovski et al (2009) revealed results that provided experimental evidence for the potential efficacy of an early intervention for stuttering using rhythmic treatment termed syllable-timed speech (STS). All three participants used in the study by Trajkovski et al (2009), maintained a consistent reduction in their “beyond clinic” stuttering, which was associated with the introduction of the treatment used in the study. Such therapies are often individualized to meet specific needs of the client and such approaches can often have the unintended consequence of making the fluent speech produced by the PWS sound unnatural to both the person who stutters and listeners. Stuttering and Speech Naturalness Both the core behaviors of stuttering and, in some cases, the treatment strategies taught to clients in therapy can create speech patterns that sound unnatural to listeners. A primary goal of any therapeutic procedure for a speech disorder is to maximize how natural the speech patterns sound relative to a referent population. The importance of this distinction between measures such as stuttering behavior and speech naturalness is reflected in a significant body of research focused on speech naturalness as a psychophysical dimension in persons who stutter. Recognizing this distinction, the most recent edition of the Stuttering Severity Instrument (SSI4), arguably one of the most common clinical assessment tools used to assess stuttering behavior, added a measure of speech natu