title: Feedforward and feedback control in apraxia of speech: effects of noise masking on vowel production.
abstract: OBJECTIVE
  This study was designed to test two hypotheses about apraxia of speech (AOS) derived from the Directions Into Velocities of Articulators (DIVA) model (Guenther et al., 2006): the feedforward system deficit hypothesis and the feedback system deficit hypothesis.
  
  
  METHODS
  The authors used noise masking to minimize auditory feedback during speech. Six speakers with AOS and aphasia, 4 with aphasia without AOS, and 2 groups of speakers without impairment (younger and older adults) participated. Acoustic measures of vowel contrast, variability, and duration were analyzed.
  
  
  RESULTS
  Younger, but not older, speakers without impairment showed significantly reduced vowel contrast with noise masking. Relative to older controls, the AOS group showed longer vowel durations overall (regardless of masking condition) and a greater reduction in vowel contrast under masking conditions. There were no significant differences in variability. Three of the 6 speakers with AOS demonstrated the group pattern. Speakers with aphasia without AOS did not differ from controls in contrast, duration, or variability.
  
  
  CONCLUSIONS
  The greater reduction in vowel contrast with masking noise for the AOS group is consistent with the feedforward system deficit hypothesis but not with the feedback system deficit hypothesis; however, effects were small and not present in all individual speakers with AOS. Theoretical implications and alternative interpretations of these findings are discussed.
authors.forename: Edwin
authors.initials: E
authors.lastname: Maas
authors.forename: Marja-Liisa
authors.initials: ML
authors.lastname: Mailend
authors.forename: Frank H
authors.initials: FH
authors.lastname: Guenther
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001037:Aphasia / Q000503:physiopathology / Q000523:psychology; D001072:Apraxias / Q000503:physiopathology* / Q000523:psychology; D016022:Case-Control Studies; D030141:Feedback, Psychological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009622:Noise; D010470:Perceptual Masking; D010700:Phonetics; D013060:Speech / Q000502:physiology*; D013061:Speech Acoustics; D013068:Speech Production Measurement; D055815:Young Adult