| While previous studies have revealed areas vulnerable to disfluency at the word level in stuttering, identifying the factors responsible for this instability has proved difficult; moreover, the inconsistent results are complicated by a failure to control for the effects of phrasal prosody, which govern such word-level factors as lexical stress. It was hypothesized in this dissertation that stuttered disfluencies are caused by a deficit in building prosodic structure. Specifically, it was predicted that words bearing a higher level of metrical prominence would be more prone to disfluent production in stutterers' speech than words of lower prominence. The second prediction was that, for stutterers, advance detection of underlying breakdowns in prosodic structure creation ('target disfluencies') would result in a categorically different type of disfluency ('anticipatory disfluencies'), with the latter surfacing in predictable locations of an intonation phrase---crucially, prior to the target disfluency. For control subjects, it was hypothesized that while some anticipatory disfluencies would surface, they would do so less frequently than for stutterers, and in prosodically unpredictable locations.; In a story-telling task performed by four stutterers and four control subjects, it was found that, for stutterers, metrically prominent words attracted a higher rate of disfluencies than did unaccented words. In addition, analyses of the prosodic context of each disfluency revealed that stutterers produced significantly more anticipatory disfluencies than did controls.; In order to determine more accurately the location of stutterers' target disfluencies, a reference prosody was collected by instructing control subjects to read scripts of stutterers' narrations. Comparisons of script results with the stutterers' natural data further confirmed that target disfluencies occurred most often on pitch---accented words particularly the first and final pitch-accented word of an intermediate phrase. The consistent location of disfluencies on roughly every other pitch-accented word, meanwhile, suggested the constraining influence of smaller prosodic structures on disfluency distribution patterns.; It was concluded that while normal disfluencies are produced as a result of errors in either conceptual or phonological encoding, stuttered disfluencies are triggered by an impairment in prosodic structure generation---specifically, in building intermediate phrases and, to a lesser degree, smaller units within the ip. |
