توانایی های شنوایی سخنرانانی که همچنان لکنت زبان آنها باقی مانده یا بهبود پیدا کرده است

Objective The purpose of this study was to see whether participants who persist in their stutter have poorer sensitivity in a backward masking task compared to those participants who recover from their stutter. Design The auditory sensitivity of 30 children who stutter was tested on absolute threshold, simultaneous masking, backward masking with a broadband and with a notched noise masker. The participants had been seen and diagnosed as stuttering at least 1 year before their 12th birthday. The participants were assessed again at age 12 plus to establish whether their stutter had persisted or recovered. Persistence or recovery was based on participant's, parent's and researcher's assessment and Riley's [Riley, G. D. (1994). Stuttering severity instrument for children and adults (3rd ed.). Austin, TX: Pro-Ed.] Stuttering Severity Instrument-3. Based on this assessment, 12 speakers had persisted and 18 had recovered from stuttering. Results Thresholds differed significantly between persistent and recovered groups for the broadband backward-masked stimulus (thresholds being higher for the persistent group). Conclusions Backward masking performance at teenage is one factor that distinguishes speakers who persist in their stutter from those who recover.

Stuttering often starts in childhood, though the problem frequently remits before teenage. Statistics about recovery during childhood were given by Andrews et al. (1983). They analyzed results from several studies and estimated that 75% of those stuttering at age 4 years, 50% of those stuttering at age 6 years, and 25% of those stuttering at age 10 years, recovered by the time they reached 16 years of age. If the problem continues to around teenage, the chance of recovery decreases. Thus, Andrews and Harris's (1964) survey data show that no child who was stuttering when they passed age 12 years recovered by age 16 years. (The survey ceased when participants were around this age.) Recovery and persistence of stuttering has been assessed in several different ways. For instance, Andrews and Harris (1964) used a population-based sample of all children born between May and June 1947 in Newcastle-on-Tyne in the United Kingdom. Initially, there were 1142 respondents. The study only located a small number of children who stuttered and this subsample is not considered adequate according to some authorities (Yairi & Ambrose, 2005). Also, audio recordings do not appear to have been made for their participants. Thus, clinicians seem to have made their speech-based assessments in real time. The approach of Yairi and Ambrose (2005) has been to locate speakers who are close to the onset of their stuttering and follow them up, typically to about age 8. The children are recorded and have been assessed on various language, motor and demographic instruments longitudinally. Members of this team are clinically trained. Diagnosis of stuttering in such very young children is not always easy, even for clinicians (as Yairi's group's own work shows). Also recovery is not complete by age 8 (Andrews et al., 1983), so it is possible that some participants who have not recovered by this age will do so subsequently (up to age 12 according to Andrews & Harris, 1964). Our own work examines children from as near to 8 years as is possible and re-examines them at the minimum age of 12 years. Ages at initial testing are partly determined by the clinical populations that are available. The things that commend studying children at these ages are: (1) that the test range extends before and after the age at which most recovery is complete, (2) there is a realistic expectation that children at these ages can perform in the procedures required for testing (such as those used for hearing assessment in the current study), and (3) the age range complements that of Yairi and co-workers so it provides information their study cannot (and conversely, their study provides information which ours cannot). The present study examines the extent to which auditory functioning is predictive of recovery from stuttering. The current study examined whether teenage participants who recovered or persisted in the disorder, differed in their performance on a range of auditory tasks. In the remainder of this section, (1) the criteria used for classifying participants who stutter as recovered or persistent are outlined and (2) the reasons for thinking auditory performance might differ between the two subgroups of participants who stutter are presented. A participant may be considered to have recovered from stuttering (recovered developmental stutterer, RDS) if he or she (1) has been diagnosed as stuttering in childhood, (2) but is regarded as fluent at age 12 (Andrews & Harris, 1964). A past history of stuttering can be established by personal report (Wingate, 1976). However, a more satisfactory way is to obtain an independent clinical assessment at an age before recovery has taken place (at least 1 year before assessment of recovery in the work reported below). Speech samples obtained at this earlier age provide an objective record of the speaker's previous status (Wingate, 2002). The samples need to be analyzed using a standardized measurement instrument designed to assess frequency and severity of stuttering (Riley, 1994). Recovery is generally considered to be associated with a reduction in the frequency and severity of stuttering (e.g. Ingham, 1984, Starkweather, 1993, Yairi, 1993 and Yairi, 1996). To establish any such reduction, additional speech samples need to be obtained and analyzed using the standardized measurement instrument again (Riley, 1994) when the child passes age 12 by which time recovery will have taken place if it was going to happen at all (Andrews & Harris, 1964). It is possible that other difficulties remain even when there is a reduction in characteristics of stuttering in the speech (in which case recovery is only partial). Examples of such characteristics are speech naturalness (Lees, 1994), and the overall effect of stuttering on the speaker's ability to communicate (Yaruss, 2001). These are characteristics that are determined during early clinical assessments, but these are not usually available at age 12, particularly for cases where speakers have recovered because they typically do not see their clinician around this age. These aspects of communication were also assessed at teenage: (a) by the children who stutter, (b) by their parents, and (c) by researchers. A participant may be considered to persist in stuttering (persistent developmental stutterer, PDS) if he or she (1) has a past history of stuttering, and (2) is regarded as still stuttering at age 12. Participants who persist in their stuttering had to be considered to be stuttering by an independent clinician, and for this to be reflected in the analysis of the samples of their speech (Riley, 1994) at least 1 year before they passed age 12. They also had to have continuing difficulty at age 12 plus, based on analyses of their speech samples (Riley, 1994) and as assessed: (a) by the children who stutter, (b) by their parents, and (c) by researchers. There are several lines of evidence that suggest that auditory processes may be involved in some way in stuttering. First, fluency control improves in participants who stutter if the sound of the voice is altered before the participant hears it. Various forms of noise maskers (Cherry & Sayers, 1956; Dewar, Dewar, Austin, & Brash, 1979), as well as frequency shifted (Howell, El-Yaniv, & Powell, 1987) and delayed (Ryan, 1974), versions of the voice, all improve control in participants who stutter. The improvements could be the result of a deficit in the auditory system whose effects are attenuated when each of these alterations is made. Second, there are a number of reports of physiological differences between speakers who stutter and fluent controls, some of which discuss the auditory cortex and its relationship to other cortical and subcortical regions. For example, Sommer, Koch, Paulus, Weiller, and Buchel (2002) reported decreased fractional anisotropy diffusion in white matter in speakers who persist in their stutter compared to controls. They interpreted this finding as showing decreased myelinisation below the left sensorimotor representation of the tongue and larynx. Also, in an anatomical study using MRI, Foundas, Bollich, Corey, Hurley, and Heilman (2001) reported abnormalities of size and asymmetry in speakers who persist in their stutter in the planum temporale. The focus of the current study is on auditory functioning assessed behaviorally. Auditory masking paradigms are often used to assess participants’ hearing ability. A probe tone that is masked by a noise stimulus should not be distinguishable from a masking noise alone. The paradigms used to assess performance with masked sounds present two or more sounds (three are used in the work below), all of which have the masking sounds, but only one of which has the probe tone. Listeners are required to indicate which interval contains the sound with the probe tone. The test starts with the probe tone loud enough to be easily distinguishable from the masking sound. Over a series of trials, the level of the probe tone is reduced until listeners cannot hear the probe and have to guess. At this point, the level of the probe tone is around the threshold appropriate for that listener for the given noise masker level. Listeners are encouraged to guess when they are unsure, and when they do so, they will make a correct response by chance on some of the trials (approximately 50% of the times when two intervals are presented and 33% of the times when three intervals are presented). To ensure the correct response was not a lucky guess, the level of the probe tone is increased slightly to bring it above the threshold for detection, and the test repeated. After the threshold has been crossed by increasing and decreasing the level of the probe tone, the true threshold can be estimated. Thresholds have been traditionally estimated like this for no masker (absolute threshold) and with a variety of different maskers. One important type of masking stimulus is a broadband masking stimulus presented concurrent with the probe. This is called a simultaneous masker and performance with this stimulus reflects cochlear processes (Moore, 1982). Masking stimuli consisting of a probe tone followed by the masking stimulus (backward-masked stimuli) are being extensively investigated at present. Interest in backward masking was prompted by the work of Tallal and Piercy (1973), which was intended to establish auditory involvement in another language disorder, specific language impairment (SLI). SLI shares with stuttering difficulty in some aspects of speech production including late language onset (Andrews & Harris, 1964), word-access difficulties (Howell & Sackin, 2001) and possible problems dealing with grammatically complex structures (Howell & Dworzynski, 2005), but also involves deficits in comprehension in children who appear to be unimpaired in other cognitive tasks. Tallal and Piercy (1973) proposed that SLI stems from difficulties in processing the temporal structure of sounds, which would affect speech and language ability. Wright et al. (1997) conducted auditory backward and simultaneous masking tests with SLI children. Consistent with the view of an auditory deficit involving processing of temporal structure, Wright et al. (1997) found that SLI children have higher backward masking thresholds, but similar simultaneous masking thresholds, compared with control children. There are two studies where backward masking performance of participants who stutter has been compared with fluent controls. Howell, Rosen, Hannigan, and Rustin (2000) compared backward masking performance of stuttering and control participants aged between 8 years 1 month and 12 years 6 months. The participants who stutter had poorer backward masking performance compared with the fluent controls. In more extensive testing, Howell and Williams (2004) tested the auditory sensitivity of 37 participants who stutter and 44 participants who do not stutter, aged between 8 and 19 years in the following five listening conditions: (1) absolute threshold, (2) simultaneous masking, (3) backward masking, (4) notched backward masking, and (5) simple dichotic (simultaneous) masking. Howell and Williams (2004) found no deficit in children who stutter relative to fluent controls in backward masking performance, although there was some evidence that the thresholds changed during development at different rates for the two groups of participants. Part of the reason that no difference was found between the groups of participants could be that only PDS show a backward masking deficit whereas RDS operate like fluent controls, and that Howell et al.'s (2000) sample included more participants destined to persist in the disorder. The hypothesis tested here is that PDS participants have a backward masking deficit compared with the RDS participants. Four auditory conditions were selected from Howell and Williams (2004). These were absolute threshold and simultaneous masked threshold as controls (neither Howell et al., 2000, nor Howell and Williams found differences between PWS and controls for these conditions, so no differences would be expected between PDS and RDS speakers) and two conditions that involved variants of backward masking stimuli. The auditory tests were made when the participants were aged between 12 and 17 years, i.e. at an age at which the designation as PDS or RDS could be made. Howell and Williams (2004) have shown that participants of these ages can perform the task. In summary, PDS speakers’ and RDS speakers’ performance with backward masking stimuli was examined (backward masking performance is regarded as reflecting aspects of speech processing performance). The question examined was whether the PDS speakers alone show backward masking deficits. This may help resolve some contradictory indications in the literature as to whether speakers who stutter have backward masking deficits, and indicate whether performance with these stimuli is a sign of PDS.

The results show that PDS participants have poorer sensitivity with band-limited backward masking stimuli compared with the RDS participants (a difference of about 10 dB). At present it is not known whether the same results (backward masking) apply at ages closer to onset of the disorder and, if so, whether this could be used as an indicator of prognosis of the disorder.