title: The effect of speaking rate on serial-order sound-level errors in normal healthy controls and persons with aphasia.
abstract: BACKGROUND
  Although many speech errors can be generated at either a linguistic or motoric level of production, phonetically well-formed sound-level serial-order errors are generally assumed to result from disruption of phonologic encoding (PE) processes. An influential model of PE (Dell, 1986; Dell, Burger & Svec, 1997) predicts that speaking rate should affect the relative proportion of these serial-order sound errors (anticipations, perseverations, exchanges). These predictions have been extended to, and have special relevance for persons with aphasia (PWA) because of the increased frequency with which speech errors occur and because their localization within the functional linguistic architecture may help in diagnosis and treatment. Supporting evidence regarding the effect of speaking rate on phonological encoding has been provided by studies using young normal language (NL) speakers and computer simulations. Limited data exist for older NL users and no group data exist for PWA.
  
  
  OBJECTIVE
  This study tested the phonologic encoding properties of Dell's model of speech production (Dell, 1986; Dell,et al., 1997), which predicts that increasing speaking rate affects the relative proportion of serial-order sound errors (i.e., anticipations, perseverations, and exchanges).
  
  
  METHODS
  The effects of speech rate on the error ratios of anticipation/exchange (AE), anticipation/perseveration (AP) and vocal reaction time (VRT) were examined in 16 normal healthy controls (NHC) and 16 PWA without concomitant motor speech disorders. The participants were recorded performing a phonologically challenging (tongue twister) speech production task at their typical and two faster speaking rates.
  
  
  RESULTS
  A significant effect of increased rate was obtained for the AP but not the AE ratio. Significant effects of group and rate were obtained for VRT.
  
  
  CONCLUSIONS
  Although the significant effect of rate for the AP ratio provided evidence that changes in speaking rate did affect PE, the results failed to support the model derived predictions regarding the direction of change for error type proportions. The current findings argued for an alternative concept of the role of activation and decay in influencing types of serial-order sound errors. Rather than a slow activation decay rate (Dell, 1986), the results of the current study were more compatible with an alternative explanation of rapid activation decay or slow build-up of residual activation.
authors.affiliation: Department of Communication Science & Disorders, University of Pittsburgh.
authors.forename: Tepanta R D
authors.initials: TR
authors.lastname: Fossett
authors.affiliation: Department of Communication Science & Disorders, University of Pittsburgh; Geriatric Research Education and Clinical Center, VA Pittsburgh Healthcare System.
authors.forename: Malcolm R
authors.initials: MR
authors.lastname: McNeil
authors.affiliation: Department of Communication Science & Disorders, University of Pittsburgh; Geriatric Research Education and Clinical Center, VA Pittsburgh Healthcare System.
authors.forename: Sheila R
authors.initials: SR
authors.lastname: Pratt
authors.affiliation: Department of Communication Science & Disorders, University of Pittsburgh; Center for the Neural Basis of Cognition, University of Pittsburgh and Carnegie Mellon University.
authors.forename: Connie A
authors.initials: CA
authors.lastname: Tompkins
authors.affiliation: Department of Speech Pathology & Audiology, West Virginia University.
authors.forename: Linda I
authors.initials: LI
authors.lastname: Shuster
keywords: aphasia; phonologic encoding; serial-order errors; speech production; speech rate