title: Individual variability in delayed auditory feedback effects on speech fluency and rate in normally fluent adults.
abstract: OBJECTIVE
  Delayed auditory feedback (DAF) is known to induce stuttering-like disfluencies (SLDs) and cause speech rate reductions in normally fluent adults, but the reason for speech disruptions is not fully known, and individual variation has not been well characterized. Studying individual variation in susceptibility to DAF may identify factors that predispose an individual to be more or less dependent on auditory feedback.
  
  
  METHODS
  Participants were 62 normally fluent adults. Each participant performed a spontaneous speech task in 250-ms DAF and amplified nondelayed auditory feedback (NAF) conditions. SLDs, other disfluencies (ODs), speech errors (SEs), and articulation rate (AR) were measured under each condition.
  
  
  RESULTS
  In the DAF condition, SLDs and SEs significantly increased, and AR decreased. Sex had a limited effect in that men exhibited higher rates of ODs and faster AR than women. More important, parametric cluster analysis identified that 2- and 3-subgroup solutions reveal important variation that differentiates tendencies toward disfluency changes and rate reduction under DAF, which are theoretically and empirically preferred to a single-group solution.
  
  
  CONCLUSIONS
  Individual variability in response to DAF may be accounted for by subgroups of individuals. This suggests that certain normally fluent individuals could be more dependent on intact feedback to maintain fluency.
authors.affiliation: Chosun University, Gwangju, Korea. hchon@chosun.ac.kr
authors.forename: Heecheong
authors.initials: H
authors.lastname: Chon
authors.forename: Shelly Jo
authors.initials: SJ
authors.lastname: Kraft
authors.forename: Jingfei
authors.initials: J
authors.lastname: Zhang
authors.forename: Torrey
authors.initials: T
authors.lastname: Loucks
authors.forename: Nicoline G
authors.initials: NG
authors.lastname: Ambrose
mesh_terms: D000293:Adolescent; D000328:Adult; D001184:Articulation Disorders / Q000503:physiopathology*; D001308:Auditory Perceptual Disorders / Q000503:physiopathology*; D016000:Cluster Analysis; D056228:Feedback, Sensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010700:Phonetics; D012737:Sex Factors; D013060:Speech / Q000502:physiology*; D013067:Speech Perception / Q000502:physiology; D013342:Stuttering / Q000503:physiopathology*; D014831:Voice / Q000502:physiology*; D055815:Young Adult