Speech-language pathologists universally agree about the importance of motor learning principles (e.g., reinforcement, practice, feedback) to optimize how people learn and remember speech therapy skills. Duffy (2005) stated, "principles of motor learning should influence the structure of speech-oriented treatment" (p. 449). Similarly Yorkston, Beukelman, Strand, and Hakel (2011) stated, "the clinician must address factors that facilitate motor learning" (p. 388). Max and Caruso (1998) proposed that adoption of a motor learning framework allowed for the generation of empirically testable hypotheses regarding the effects of different variables on stuttering during treatment.

The vast majority of information we have about principles of motor learning is based on studies of nonspeech movements (e.g., golfing) of healthy individuals (e.g., cigar rollers; Schmidt & Wrisberg, 2004). Unfortunately we know very little about how people with various speech disorders learn and remember speech therapy skills. For example, Duffy (2005) acknowledged it is unclear if people with speech disorders "can ever get beyond the transition phase of learning" (p. 449). Wambaugh, Martinez, McNeil, and Rogers (1999) lamented "with respect to improving and maintaining sound production with apraxic speakers, very little is known about post-treatment maintenance" (p. 832). Yairi and Seery (2011) admitted it is not known, "if motor learning principles are applicable to speech fluency learning" (p. 189).

Unjustified assumptions

It cannot be assumed that people with motor speech disorders learn speech motor skills the same way as people who don't have these disorders. Neither can it be assumed that speech motor skills will abide by the same principles of motor learning as non-speech motor learning principles. There is an essential need for research to characterize the capabilities/difficulties of people with motor speech and fluency disorders when learning and remembering speech therapy skills. Once this knowledge base is established; research can focus on how motor learning principles can be manipulated to optimize speech therapy.

Stages of motor learning

Motor learning typically progresses through stages over practice (Anderson, 1982). Initially you pay a great deal of attention to what you are doing and feedback about your success guides future performance. For most motor skills a transition is made from declarative learning strategies (conscious strategy planning and attention to feedback; Schmidt & Wrisberg, 2004), to procedural strategies (unconscious, self-correcting muscle coordination strategies; Saint-Cyr, Taylor, & Lang, (1988). In early stages of learning any distraction can negatively affect your performance. After a substantial amount of practice the skill is performed more automatically and performance is less susceptible to distractions (Schmidt & Wrisberg, 2004).

Motor learning variables

A comprehensive overview of variables that affect motor learning, retention, transfer/generalization is beyond the scope of this brief review. Instead this paper will focus on practice schedules and feedback, for which there is excellent existing research for both procedural (motor) and declarative (verbal/cognitive) learning skills (see Schmidt & Bjork, 1992).

Practice and retention

Distributed schedules, where you practice several different skills within one practice session, result in better retention (remembering) of the skill in the long term. In contrast, massed practice schedules, where you practice the same skill repetitively is not as effective in the long term and this is true for motor and verbal skills (Magill & Hall, 1990; Shea & Morgan, 1979). For example, it is most useful to practice dribbling, shooting and running in one practice session rather than just dribbling. Similarly, variable practice results in better retention and generalization of knowledge to novel situations than does constant practice for both motor and verbal skills (Schmidt & Bjork, 1992). This means it is better to practice shooting hoops from 2', 3' and 4', rather than just from 3', even if, for the final test, the hoop is 3' away (Kerr & Booth, 1978). Finally, research also shows better retention of motor and verbal skills for distributed practice over time (have more short sessions vs. fewer long sessions; Baddeley, & Longman, 1978).

Feedback

Enhanced feedback in different modes (e.g., audio, visual, tactile, etc.) can be used to improve performance during the first practice session (Schmidt & Bjork 1992). However, less feedback is better for long-term retention of motor and verbal skills. Infrequent feedback results in better long-term retention of a skill than more frequent feedback (e.g., feedback every 15 trials vs. every trial; Scott, Page, & Jog, 2002; Vanvliet & Wulf, 2002).

Early stages of motor learning

Both Mentis et al. (2003) and Frith, Bloxham, and Carpenter (1986) found that control subjects showed marked improvement in performance during very early trials while patients with Parkinson's disease (PPD) did not. In a comprehensive review, St-Cyr (2003) suggested that this rapid improvement in performance during early trials reflected "acquisition of set" and that PPD had difficulty with this.

Similar to PPD, persons who stutter (PWS) were slower than control subjects to say nonsense syllables ("PO"; Smits-Bandstra & Gracco, 2011), long nonsense words (PABATABAGAPAGABATAPA; Smits-Bandstra & De Nil, 2009) or read aloud sentences (Cooper & Allen, 1977) on early practice trials. This "slow start" for early trials particularly, was also noted in a review of PWS' performance for reaction time studies in general (Smits-Bandstra, 2010).

Later stages of motor learning

It remains unclear if PPD or PWS successfully transition to the automatic stage for speech skills after practice. Dual-tasks are well established in the literature as a means to investigate the level of automatization of a skill (Doyon et al., 1998). Patients with Parkinson disease (Benecke et al., 1986; Doyon et al., 1997; 1998; Thomas, Reymann, Lieury, & Allain, 1996) demonstrate poor performance on dual tasks relative to control subjects, indicating lower levels of automaticity after practice. Similar to PPD, PWS have demonstrated difficulties in the face of various cognitive and/or motoric dual task demands (Smits-Bandstra & De Nil, 2009; Smits-Bandstra, De Nil, & Rochon, 2006).

Practice

After the "slow start" the motor learning performance of PWS is often equivalent to control subjects for short and simple tasks, for example when asked to say nonsense syllables (e.g., "PO"; Smits-Bandstra & Gracco, 2011) or perform simple button presses (see review by Smits-Bandstra, 2010). However, research suggests that the motor performance of people who stutter does not appear to benefit from practice to the same extent as people who do not stutter for sequencing tasks (Ludlow, Siren, & Zikira, 1997; Smits-Bandstra & De Nil, 2009; Webster, 1986). Neither do PPD appear to benefit from practice to the same extent as controls for sequence learning tasks (Schulz et al., 2001; Smith & McDowall, 2004; or see Smits-Bandstra & De Nil, 2007 for a review).

Research with PWS further suggests that certain practice schedules may be more effective for reducing stuttering. For example, Brutten and Dancer (1980) found better fluency after distributed vs. massed practice reading 100 words. PWS' performance during one practice session was optimized when practice reflected the skill to be learned as closely as possible. Bruce and Adams (1978) and Brenner, Perkins, and Soderberg (1978) found that the frequency of stuttering decreased more when PWS read a passage aloud as opposed to whispering or moving their lips. However, based on previous research, we would predict more diverse and different practice to lead to better retention of motor and verbal skills and this has not been investigated with PWS.

Retention

Studies which examined motor sequencing skills over one session or over a few days found good retention by PPD (Harrington, Haaland, Yeo, & Marder, 1990; Smits-Bandstra & Gracco, 2011), while those which looked over several weeks or months of practice found increasing differences in skill retention between PPD and control participants (Doyon et al. 1998; Mochizuki-Kawai et al., 2004; Vakil & Herishanu-Naaman, 1998).

Recently Blomgren, Roy, Collister, and Merrill (2005) concluded that some relapse appears to be inherent in most stuttering therapies. Two studies have found poor retention of speech sequencing skills by PWS relative to controls subjects after approximately one hour (Smits-Bandstra, De Nil, and Saint-Cyr, 2006), and one to three days after the initial session (Namasivayam & van Lieshout, 2008). However, retention may be intact for short simple tasks. Smits-Bandstra and Gracco (2011) found that PWS' retention of reaction time improvements for a single syllable task ("PO") was equivalent to that of controls, with the exception of poor reaction times or "slow re-start" of the first block of the retention test seven days later.

Feedback

Differences in speed, accuracy, and variability between PPD and control subjects are minimized when performance is guided by external sensory cues (Georgiou et al., 1993, 1994; Majsak et al., 1998 (cited in Fattaposta 2002) Liu, Tubbesing, Aziz, Miall, & Stein, 1999). In addition, differences in sequence learning between PPD and control subjects are minimized when PPD are provided with enhanced external feedback/reinforcement (Mentis et al., 2003; Catalan et al., 1999). Based on a comparison of PPD and control participants on a sequence learning study, Dominey et al. (1997) concluded that PPDs' procedural learning appeared relatively intact only when knowledge of results was present to guide learning. In concordance, Guadagnoli, Leis, Van Gemmert, and Stelmack (2002) reported Parkinson patients required 100% knowledge of results (relative to 20% for control participants) in order to demonstrate commensurate retention of a simple timing movement.

Similar to PPD, research shows that the motor performance of PWS is enhanced by enhanced visual feedback (Archibald and De Nil, 1991; De Nil & Abbs, 1999; Loucks & De Nil, 2001), and external movement timing cues (Boutsen et al., 2000; Lang & Fishbein, 1983; Yahalom et al., 2004). In particular, the stuttered speech of PWS is less severe when external sensory cues are provided (e.g., singing, chorus speech; for review see Venkatagiri, 2004). However, based on previous research we would predict that less frequent feedback would lead to better retention of learned motor and verbal skills and this has not been investigated in PPD or PWS.

Neuroimaging of treatment effects

Practice leads to successful changes in motor speech and fluency skills. The positive therapeutic effects of treatment for apraxia, stuttering and Parkinson's disease have been described (Wambaugh, Fliszar, West, & Doyle, 1998: O'Brian, Packman & Onslow, 2008; Sapir, Ramig, Hoyt, Countryman, O'Brien, & Hoehn, 2002). The preliminary evidence presented above suggests that practice does not result in typical motor learning and retention for PWS and PPD, therefore how do PWS and PPD learn and remember new speech therapy skills?

Several studies have been conducted to investigate the neural correlates of intensive training of speech "loudness" training in the LSVT program (Fox, Ramig, Ciucci, Sapir, McFarland, & Farley, 2006; Narayana et al., 2010). These studies seem to suggest that while treatment is effective in changing behavior, the training required to institute such a change is intensive, supplemented by many types of feedback and frequent knowledge of results, and is not accompanied by the expected neural changes in the primary motor and sensory cortices (Karni et al., 1998). Instead, these studies report increased neural activity in areas associated with "top down" (declarative) attention and monitoring, suggesting compensation and/or declarative strategy use rather than procedural motor learning per se (Fox et al., 2006; Narayana et al., 2010). This emphasis on monitoring may have evolved as a response to difficulties PPD have transitioning to procedurally-based learning as well as retaining proficiency for new speech patterns.

Neuroimaging studies with PWS have found that temporary fluency-enhancing techniques (e.g., chorus reading, talking along with a metronome) caused increased compensatory activity in the right side of the brain (Jeffries et al., 2003; Preibisch et al., 2003). In contrast, treatment resulted in increased activity in both left and right hemispheres (De Nil et al., 2001; 2003; Neumann et al., 2003; Preibisch, et al., 2003). Stuttering therapy often requires PWS to pay conscious attention to details of speech performance, break complex speech tasks into smaller parts, and focus attention on how the movement feels. All of these activities result in enhanced left hemisphere activity (Beilock et al., 2002; Dogil et al., 2002; Hund-Georgiadis & von Cramon, 1999; Raichle et al., 1994).

Neumann et al. (2003) found that the brain patterns of PWS continued to reflect high levels of attention, effort, and motor control demands even after long-term, extensive practice of fluency skills. This result suggested that new speech skills taught in stuttering therapy may never become completely automatized for some PWS.

Speech therapists agree that speech therapy should be conducted according to motor learning principles. However, most motor speech and stuttering therapy programs tend to emphasize constant, massed practice with frequent feedback. Nonspeech research suggests that this type of practice/feedback is not ideal for long-term retention and generalization of skills. Furthermore recent research suggests that PWS and PPD learn and remember differently than control subjects. Clearly ongoing research is needed to explore how motor learning principles can be manipulated to optimize speech therapy for people with communication disorders.

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