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The role of knowledge of results in performance and learning of a voice motor task
Journal of Voice
Vol. 14, No. 2, pp. 137-145 © 2000 Singular Publishing Group
The Role of Knowledge of Results in Performance and Learning of a Voice Motor Task Kimberly Steinhauer and Judith Preston Grayhack Department of Communication Science and Disorders University of Pittsburgh Pittsburgh, Pennsylvania
Summary: The relationship between the provision of Knowledge of Results and the performance and learning of a voice motor task was examined. Thirty adult subjects, randomly assigned to a 100%, 50%, or No Knowledge of Results group, practiced a novel vowel nasalization task. Measures of accuracy and variability obtained during the practice session indicated influence of knowledge of results schedule on the transient effects of motor performance. Deviations from the nasalance target during the retention phase, 5 minutes later, and during a transfer phase, 24 hours later, indicated influence of knowledge of results schedule on the permanent effects of motor learning. Collective results revealed that an increase in relative frequency of knowledge of results led to a decrease in motor performance and learning of a vowel nasalization task: Both accuracy and variability were degraded as knowledge of results increased, with those subjects in the 100% group exhibiting the poorest scores. Key Words: Knowledge of Results--Practice--Nasalance
Singing teachers and voice therapists deal with improving human performance and facilitating learning through permanent behavioral changes. It is critical to understand how variables such as task and practice impact the acquisition of new motor patterns. This investigation addresses the relationship between a practice strategy using Knowledge of Results (KR) and motor acquisition and retention of a voice motor task, vowel nasalance. The purpose of the study was to determine the effect of manipulating
relative frequency of KR on performance and learning of a vowel nasalization task as measured by a nasalance score. Feedback, sensory information about a movement, remains second in importance only to practice as a variable influencing motor skill acquisition.I, 2 Voice researchers have explored the contribution of auditory feedback to voice motor control, 3 but have been less attentive to the role of extrinsic, augmented feedback in voice motor skill acquisition. 4 Due to the complexity of studying intrinsic feedback, motor learning researchers have concentrated on manipulating variables of extrinsic feedback such as KR. 1,5-10 KR is verbal, or verbalizable, terminal augmented feedback about the outcome or nature of the result in terms of the environmental goal (eg, "The target was 80, your score was
Accepted for publication April 20, 1999. Address correspondence and reprint requests to Kimberly Steinhauer, Department of Communication Science and Disorders, 4033 Forbes Tower, University of Pittsburgh, Pittsburgh, PA 15260 USA Presented at the Twenty-Seventh Annual Symposium: Care of the Professional Voice; June 2, 1998; Philadelphia, PA
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72."). Relative frequency of KR refers to the percentage of trials in which KR is offered. Within the confines of a motor learning experiment, subjects practice on a selected motor task, and then progress is documented as a function of practice trial. Salmoni, Schmidt, and Walter advocated distinguishing between KR effects on performance and KR effects on learning. 1 Performance effects typically measured during the acquisition phase are considered as temporary or transient changes. Learning effects measured during retention and transfer phases are considered as permanent changes. Variables such as motivation and fatigue that accompany the provision of KR during acquisition have been found to contaminate motor learning results; therefore, Salmoni et al 1 suggested measuring motor learning via a retention design in which all groups are treated to a common level of the independent variable, usually no KR, following the acquisition phase. In addition, transfer designs that include a shift of the task or target as a powerful indicator of motor learning were advocated. The most compelling results of studies of motor learning have been those in which retention and transfer tests were administered after the performance effects dissipate d - r a n g i n g from as little as 5 minutes to 5 days, or 5 months postacquisition.1 Theories of motor learning underscore different roles for KR during motor skill learning. Properties of motivation, guidance, and association have been examined as possible explanations for the function of KR during motor learning.l, 2,8 Schmidt's openloop schema theory and guidance hypothesis are founded on movement categories or schemas (ie, ball pitching or pitch elevation) that are governed by a stored, generalized motor program (GMP) containing specific parameters for that action. 2,H Studies conducted within the context of Schmidt's theory showed an inverse relationship between relative frequency of KR and motor learning, regardless of the KR schedule (ie, after alternating trials, after trial block, or faded throughout practice). Increases in relative frequency of KR resulted in degraded learning effects during retention and transfer. 1,12-14 In addition, increases in relative frequency of KR increased motor performance during acquisition; 1 however, other investigations reported that an inJournal of Voice, Vol. 14, No. 2, 2000
crease in relative frequency of KR failed to produce a performance effect during acquisition.12, ~4 The alternative to the prescriptive theory of motor control and learning lies in the dynamical systems approach that describes humans as self-organizing systems capable of movement through an emergent result of changes in coordinative structures governed by underlying physical, synergetic, or ecological principles. 15,16 In the emergent context, motor learning is viewed as the integration of new coordination patterns or synergies on the background of preexisting patterns called intrinsic dynamics. 16-L8 Swinnen suggests that KR acts to either exploit or suppress the learner's intrinsic dynamics during practice. 18 Although KR has been used to describe the "to be learned" pattern, ~9 specific predictions about the frequency of KR have not been addressed due to the recent incorporation of motor learning into the dynamical theories of motor control. Regardless of the theoretical genesis, many studies have documented relationships between limb motor learning and relative frequency of KR; 20 however, few investigations have examined the impact of practice with KR on voice production. Ferrand explored the relationship between KR and phonatory stability, as indexed by jitter and shimmer. 4 Two groups of subjects practiced sustaining a n / a / f o r 2 seconds. The KR group received information on every trial about the waveform and jitter/shimmer values. A second group received no KR. Results of the transfer session, held 1 week after practice, revealed no difference between groups for either shimmer or jitter measurements, indicating no relationship between providing KR and permanent changes in phonatory stability. The disparate results within the limb and voice KR literature motivated this research project designed to determine the influence of KR on learning a voice motor task integral to optimal voice resonance. The percept nasality is modulated to some degree by varying the size of the velopharyngeal port, as well as the entire oral cavity. Volitional modification of nasality is a common goal among singers and speakers across most voice quality productions but novel to voice producers when practiced in isolation, thus providing a unique task upon which to test voice motor learning.
THE ROLE OF KNOWLEDGE OF RESULTS IN PERFORMANCE AND LEARNING OF A VOICE Although proprioceptive innervation of the velopharyngeal sphincter is limited, 21 volitional control of nasality has been documented.22, 23 Moon and Jones demonstrated dynamical properties of the velopharynx through a study in which 10 subjects successfully produced b o t h / a / a n d / i / a t 50% and 75% nasality using simultaneous phototransduction to provide visual feedback. 22 Results showed that success at achieving the target was attributable to plasticity (learning) or flexibility (success without learning), two mechanisms of dynamical motor learning described by Folkins. 24 Plasticity referred to a restructuring of the physiological rule system that occurs during practice. Flexibility referred to an existing rule system confined to parameters of the coordinative structure that accounts for success at a novel task without practice. In singing instruction,25, 26 cleft palate rehabilitation, 22 and resonant voice therapy 27 clients are asked to exploit nasality to alter articulation and resonance properties of the vocal tract. Therefore, the aim of this study was to test the effects of manipulating the relative frequency of KR (100%, 50%, and no KR) during learning of a vowel nasalization task, as estimated by nasalance score. Results from the study will be interpreted within the context of Schmidt's 11 schema theory predicting differential effects of KR on performance and learning and Folkin's 24 theory predicting a possibility of no effect of KR on performance and learning due to the dynamical properties of coordinative structures.
METHODS Subjects Thirty subjects (20 women, 10 men) between the ages of 18 and 40 years were selected from the student population at the University of Pittsburgh for the study. All subjects were required to have a negative history for speech deficits, and to pass a hearing screening at 20 dB SPL. The racial, gender, and ethnic characteristics of the proposed subject population reflected the demographics of Pittsburgh and the surrounding area. Subjects were required to test within nasalance norms for the Zoo Passage as measured by the Kay Elemetrics Nasometer. All subjects were native speakers of English and vocally untrained, that is,
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had participated in less than five private speaking/singing lessons. The subjects were healthy nonsmokers, experiencing no upper respiratory or sinus infections, and free of alcohol and medications that have the potential to compromise normal voice motor control. The subjects remained naive to the specific purposes of the experiment, had no previous exposure to the experimental vocal task, and were not significantly different in their baseline performance of the task.
Apparatus The Kay Elemetrics Nasometer, a computer-assisted instrument, facilitated measurement of nasalance over time. The Nasometer is a noninvasive input device consisting of two directional microphones and a sound separator plate. The calculated nasalance score is a ratio of nasal to oral plus nasal acoustic energy for each subject. KR as nasalance score appeared on the computer monitor. The dynamic range of the Nasometer is 50 dB, thus ensuring accurate data collection on a wide range of voice intensities. Task
Acquisition~Retention The subjects were required to nasalize a sustained vowel ( / i / - - > / t / ) . To ensure stable and volitional control, each trial was 6 seconds in duration--2 seconds of oral phonation before switching to nasal for the final 4 seconds. Target nasalance score for the oral vowel was between 0% and 40%, and the target score for the nasalized vowel was 80%. Subjects proceeded with the task only after achieving the initial target for the oral vowel. Transfer The transfer task required the subjects to perform the identical task Using a new vowel,/a/.
Experimental design and procedure Acquisition Thirty subjects were assigned randomly to three groups of feedback (100% KR, 50% KR, No KR). KR as percent nasalance was administered to the subjects via a computer monitor. Subjects in the 100% KR group received immediate information afJournal of Voice, Vol. 14, No. 2, 2000
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ter every trial. The 50% KR group received immediate information after every other trial. The No KR group was not permitted to view the monitor. During initiation of the session, the experimenter provided instructions and demonstrations involving the task and apparatus. Using the nasometer, subjects practiced on four trials using a different vowel, /if, and a different nasalance target, 65%. All subjects received information in the form of nasalance score and received a countdown to prepare, initiate, and change the vocalization. Motor performance was examined during the acquisition phase consisting of 5 blocks of 8 trials. All subjects filled the 2second intertrial interval with counting by twos or threes in order to control for mental rehearsing. Retention~transfer
Learning was examined during a retention and transfer phase in which all subjects moved to a common level of the independent variable, No KR. The immediate retention phase, 5 minutes following acquisition, consisted of 2 blocks of 8 trials using the identical task. The transfer phase, 1 day after acquisition, consisted of 2 blocks of 8 trials using the transfer vowel/a/.
Data collection and statistical considerations The effect of the independent variable, KR relative frequency, was measured using the dependent variable, nasalance score. The central 2 seconds of the total nasal utterance (4 seconds in duration) were used for analysis to ensure stability of the target nasalized vowel. Performance effects were measured during the acquisition phase, and learning effects were measured during retention and transfer phases. Three dependent measures sensitive to changes in accuracy and variability 2 were calculated. Absolute error (AE) is the average absolute deviation between the subject's responses and the target:
AE - i=l
Ixi- sl rt
Absolute constant error (/CE/) is the average error in responding to the target and represents the accura-
Journal of Voice, Vol. 14, No. 2, 2000
cy and bias in the directional measures of average magnitude of response:
•
(x i - T) / C E / = i=l _ 12
Variable error (VE) is the variability of the subject about the mean response and is a measure of intraindividual response consistency:
VE =
t
~
i=1
(Xi _ .~)2
The acquisition data were analyzed in a 3 × 5 (Group × Block) ANOVA with repeated measures on the last factor. For both retention and transfer tests, the 16 trials were collapsed into one block and analyzed in univariate ANOVAs (group as the independent variable). Alpha was set at the .05 level, and appropriate post hoc tests were performed to elicit specific group or block differences.
RESULTS Group mean and standard deviation data for the dependent measures are listed in Table 1. The dependent measures as a function of trial block on a performance curve depict group differences in Figure 1 (/CE/), and Figure 2 (VE). The Pearson product moment correlation for accuracy measures AE and /CE/, r = .98, indicated that the measures were redundant; therefore, o n l y / C E / i s reported as a measure of accuracy and bias that is independent of V E ) 2 One outlier with scores consistently 2 standard deviations from the mean was discarded from the No KR group.
Acquisition Results for the/CE/analysis showed a significant group difference F(2,104 ) = 4.70, P<.05 (Figure 1). Post hoc Student-Newman-Keuls multiple comparisons revealed significant differences between 100% KR (M = 14.08, SD = 15.18) and 50% KR (M = 4.96, SD = 4.09), and between 100% and no KR (M = 6.19, SD = 5.21) groups, P<.05. There were no
THE ROLE OF KNOWLEDGE OF RESULTS I N PERFORMANCE AND LEARNING O F A VOICE
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T A B L E 1. Group Means and Standard Deviatons in %
Nasalance for Feedback Group Acquisition
Retention
Transfer
100% KR /CE/
14.08 (15.18)*
8.61 (6.58)
25.20 (16.82)*
VE
7.70 (6.76)
7.10 (4.90)*
6.94 (4.04)
/CE/
4.96 (4.09)*
5.63 (4.15)
12.20 (5.64)*
VE
5.77 (5.81)
3.80 (2.40)*
6.13 (3.48)
/CE/
6.19 (5.21)*
6.19 (5.21)
14.57 (7.55)
VE
5.29 (5.54)
3.60 (0.70)*
6.95 (6.89)
50% KR
No KR
Mean (Standard Deviation) *P <.05
/CE/ 30 25
~
20
¢
N o KR
,,~ 15
--m-- 50% KR
~
~100%KR
10 5 0 0
I 1
t 2
I 3
I 4
I 5
I
I ret
I trans
Block
F I G 1. Group mean five-block absolute constant error (/CE/) scores in % nasalance for acquisition (Block 1-5), retention (ret), and transfer (trans).
VE
12 10
tU >
8
;
N o KR
6
--
50% KR 100% KR
4 2 0 0
I 1
I 2
I 3
I 4
I 5
I
I ret
I trans
Block
F I G 2. Group mean five-block variable error (VE) scores in % nasalance for acquisition (Block 1-5), retention (ret), and transfer (trans).
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K I MB E R LY STEINHAUER AND JUDITH PRESTON GRAYHACK
other main effects or interactions. The group differences in/CE/indicate that accuracy to the nasalance target was enhanced by decreasing the relative frequency or withholding KR, with 100% KR leading to detrimental decreases in accuracy. Results for the VE analysis showed significant block differences across KR conditions in the acquisition phase, F(4,104 ) = 2.62, P<.05 (Figure 2). Post hoc Student-Newman-Keuls multiple comparisons revealed significant differences between Block 1 (100% K R M = 11.09, SD = 8.27; 50% KR M = 7.17, SD = 6.27; No KR M = 8.03, SD = 9.19) and Block 5, (100% KR M = 6.51, SD = 3.75; 50% KR M = 3.50, SD = 1.21; No KR M = 3.68, SD = 1.63), P<05. There were no other main effects or interactions. The block difference in VE indicates that variability about the subject's nasalance mean was decreased by practice from Block 1 to Block 5. Retention Differences in /CE/ measures were not great enough to elicit significant results; however, results for the VE analysis showed significant feedback differences in the retention phase, F(2,26) = 3.62, P<.05 (Figure 3). Post hoc Dunnett's multiple comparisons revealed significant differences between 100% KR ( M = 7.10, SD = 4.90) and 50% KR ( M = 3.80, SD = 2.40) and between 100% KR and no KR (M = 3.60, SD = .70) groups, P<.05. The group differences in VE indicate that variability about the subject's nasalance mean was reduced by decreasing the relative frequency or withholding KR, with 100% KR leading to detrimental increases in variability. Transfer Results of the/CE/analysis indicated significant group differences for the Transfer phase F(2,26/ -4.06, P<.05 (Figure 2). Post hoc Student-NewmanKeuls multiple comparisons revealed significant differences between 100% KR (M = 25.2, SD = 16.82) and 50% KR (M = 12.2, SD = 5.64) groups, P<.05. The group differences for/CE/indicate that accuracy to the nasalance target was enhanced by decreasing the relative frequency or withholding KR, with 100% KR leading to detrimental decreases in accuracy. No significant differences were observed for VE measures. Journal of Voice, Vol. 14, No. 2, 2000
DISCUSSION The aim of the present study was to explore the effect of relative frequency of KR on the motor performance and learning of a vowel nasalization task. The results showed that an increase in relative frequency of KR led to a decrease in both motor performance and learning of a vowel nasalization task; however, the results revealed a curious departure from the limb motor learning literature in that No KR proved as beneficial as 50% KR. The group differences in target accuracy (/CE/) during the acquisition phase indicate that temporary effects of motor performance were enhanced by decreasing the relative frequency to 50% or withholding KR, with 100% KR leading to detrimental decreases in motor performance of a vowel nasalization task. These results are inconsistent with past studies testing Schmidt's schema theory ~ that predict increased motor performance with increased KR; however, the results of this study are consistent with more recent studies in which increased KR decreased or exhibited no effect on motor performance.12,14 Similar group differences in target accuracy (/CE/) were observed in the transfer phase, indicating that permanent effects of motor learning were enhanced by decreasing the relative frequency to 50% KR, with 100% KR leading to detrimental decreases in motor learning of a vowel nasalization task. These results are consistent with Schmidt's schema theory 11 (and collaborative studies) that predict increased motor learning with decreased relative frequency of KR.1,12-14,20
Results of the variability measure (VE) exhibited a different pattern for acquisition and retention. The block difference between Block 1 and Block 5 during acquisition reveals that practice, not amount of KR, was the most important indicator for reducing variability during motor performance of a vowel nasalization task. The group difference during retention reveals that amount of KR was the most important indicator for reducing variability in motor learning: Decreasing the relative frequency to 50% or withholding KR enhanced motor learning, with 100% KR leading to detrimental decreases in motor learning of a vowel nasalization task.
THE ROLE OF KNOWLEDGE OF RESULTS IN PERFORMANCE AND LEARNING OF A VOICE
Often overlooked in favor of accuracy measures, reductions in variability are of paramount importance as indicators of enhanced subject stability, thus motor learning.Z, 19 All subjects in this study became more consistent with practice during acquisition, but during retention, an indicator of motor learning, those subjects who received 50% or no KR were more consistent than subjects receiving 100% KR. As stated previously in the discussion of accuracy during transfer, the variability results of this study are consistent with those conducted within the context of Schmidt's schema theory of motor learning.11 The following explanations for the present result, that 100% KR degrades both accuracy and variability of motor performance and learning, have been postulated:2°,29, 30 (1) KR may become so integrated into the task that performance may be disrupted when KR is withdrawn. (2) Increased KR as extrinsic feedback may prevent subjects from attending to their own intrinsic feedback. Subjects may overfacilitate planning of the next movement and negate engaging in self-generated retrieval operations. (3) A high-frequency KR schedule may lead subjects to produce excessive response variability during practice or maladaptive short-term corrections, thus preventing the development of a stable movement representation or motor program. Maladaptive corrections occur in situations where the motor system is successful at obtaining the target but not capable of exact precision due to neuromuscular variability. Perhaps the target of 80% nasalance was too precise for the subjects to master, and a range of 75% to 85% nasalance would have been more accessible. The maladaptive correction theory could also explain why the jitter and shimmer values in Ferrand remained unresponsive to differences in the provision of KR. 4 Although findings that 100% KR leads to decreased motor learning are common, 20 less common are results similar to the present study in which a group receiving No KR performed as well as a group receiving information. Results of accuracy measures in acquisition (Figure 1) and variability measures during retention (Figure 2) reveal that groups receiving 50% and No KR performed similarly. An explanation for the similarity of 50% and No KR groups lies in dynamical theories of motor con-
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trol. 15,24 Moon and Jones reported evidence of suc-
cess without learning as subjects achieved the novel task of velopharyngeal closure on first attempts. 22 In the context of Folkins, 24 they attributed this success as compatible with the function of forced-variation flexibility during motor learning involving coordinative structures. Folkins contends "when a rule system is set up through a coordinative structure, it is not necessary to go through an adaptation process to find novel solutions fitting the coordinative structure."24(pl12) In the present study, it is possible that the target of 80% lies in the optimal range of nasalance for the production of the vowel / 7/, rendering KR futile for successful completion of the task; however, too much information, as in the case of 100% KR, was so powerful that it interfered with the optimal movement of the nasalization coordinative structure during both performance and learning phases. Similar results were obtained during experiments in which subjects were provided with erroneous KR that overrode correct sensory feedback to diminish target accuracy. 6 Remaining in the dynamical context, it is possible to explain the decreased accuracy and increased variability of producing the v o w e l / a / a t 80% nasalance during the transfer phase (Figure 1). Moon and Jones reported that the v o w e l / a / w a s more accurately produced at 50% closure than the vowel/i/. 22 Although the acoustic nasalance score is once removed from closure percents of phototransduction, it appears as if the vowel/a/is more optimally nasalized at a lower percent than the vowel/i/. These results also are consistent with acoustic and perceptual data showing characteristic patterns of nasality on the basis of tongue height for the v o w e l s / i / a n d / a / ) ~,32 Due to tongue height, the nasalization o f / i / r e q u i r e d less coupling with the nasal cavity than that required for a nasalized production of the vowel/a/. Finally, a second explanation for the similar behavior of the No KR to the 50% K R group lies in methodological limitations of the study. The sample could have been too small to elicit the group differences. It is possible that auditory feedback provided enough information to guide the learners to the correct target; however, control of the auditory feedback loop was maintained by using only those subjects who did not receive formal voice or singing training.
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Also although group assignment was randomized, it is possible that the more proficient subjects were assigned to the No KR and 50% KR groups.
CONCLUSIONS Collective results indicate a relationship between relative frequency of KR and motor performance and learning of a vowel nasalization task. An increase in relative frequency of KR to 100% degraded both motor performance and learning as indexed by accuracy and variability measures. In acquisition, retention, and transfer, both accuracy (/CE/) and variability (VE) diminished as KR increased, with 100% KR groups exhibiting the poorest scores; however, there were minimal or no differences between groups receiving 50% or No KR. The detrimental effects of providing a high frequency of KR have been documented and are consistent within the context of Schmidt's schema theory.20, % Success at executing a voice motor goal with minimal or no KR has been documented and is consistent within the context of dynamical systems theory.22, 24 Further study incorporating auditory masking of trained and untrained subjects could provide additional evidence for the power of KR during voice motor skill acquisition. Also, future research to more discretely examine the theoretical issues of the prescriptive and dynamical systems as they pertain to KR and voice motor control is warranted.
REFERENCES 1. Salmoni AW, Schmidt RA, Walter CB. Knowledge of results and motor learning: A review and critical reappraisal. Psychological Bull, 1984;95:355-386. 2. Schmidt RA. Motor Control and Learning: A Behavioral Emphasis. 2nd ed. Champaign, Ill: Human Kinetics; 1988. 3. Buruett TA, Freedland MB, Larson CR, Hain TC. Voice FO responses to manipulations in pitch feedback. JAcoust Soc Am. 1998;103:3139-3152. 4. Ferrand CT. Effects of practice with and without knowledge of results on jitter and shimmer levels in normally speaking women. J Voice. 1995;9:419-423. 5. Bennet DM, Simmons RW. Effects of precision of knowledge of results on acquisition and retention of a simple motor skill. Percept Motor Skills. 1984;58:785-786. 6. Buckers MJ, Magill RA. The role of task experience and prior knowledge for detecting invalid augmented feedback while learning a motor skill. Q J Exp Psychol. 1995;48A: 84-97.
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7. Feltz DL, Landers DM, Becker BJ. A revised meta-analysis of the mental practice literature on motor skill learning. In: Druckman D, Swet J, eds. Enhancing Human Performance: Issues, Theories, and Techniques. Washington, DC: National Academy Press; 1988:61-101. 8. Lee TD, Swinnen SR Serrien DJ. Cognitive effort and motor learning. Quest. 1994;46:328-344. 9. Lee TD, White MA, Carnahan H. On the role of knowledge of results in motor learning: exploring the guidance hypothesis. J Motor Behav. 1990;22:191-208. 10. Wulf G, Horstmann G, Choi B. Does mental practice work like physical practice without information feedback? Res Q Exerc Sport. 1995;66:262-267. 11. Schmidt RA. A schema theory of discrete motor skill learning. Psychol Rev. 1975;82(4):225-260. 12. Winstein CJ, Schmidt RA. Reduced frequency of knowledge of results enhances motor skill learning. J Exp Psychol. 1990;16:677-691. 13. Wulf G. The learning of generalized motor programs and motor schemata: Effects of KR relative frequency and contextual interference. J Hum Movement Stud. 1992;23: 53-76. 14. Wulf G, Schmidt RA. The learning of generalized motor programs: Reducing the relative frequency of knowledge of results enhances memory. J Exp Psychol. 1989;15:748757. 15. Kelso JA, Tuller B. A dynamical basis for action systems. In: Gazzaniga M, ed. Handbook of Cognitive Neuroscience. New York, NY: Plenum Press; 1984:321-356. 16. Wallace SA. Dynamic pattern perspective of rhythmic movement: an introduction. In: Zelaznik HN, ed. Advances in Motor Learning and Control. Champaign, Ill: Human Kinetics; 1996:155-194. 17. Newell KM. Motor skill acquisition. Ann Rev Psychol. 1991;42:213-237. 18. Swinnen SR Information feedback for motor skill learning: a review. In: Zelaznik HN, ed. Advances in Motor Learning and Control. Champaign, Ill: Human Kinetics; 1996:37-66. 19. Schoner G, Zanone PG, Kelso JAS. Learning as change of coordination dynamics: Theory and experiment. J Motor Behav. 1992;24:29-48. 20. Schmidt RA, Bjork RA. New conceptualizations of practice: Common principles in three paradigms suggest new concepts for training. Psychol Sci. 1992;3(4):207-217. 21. Kuehn DR Lemme ML, Banmgartner JM. Neural Bases of Speech, Hearing and Language. Boston, Mass: CollegeHill Press; 1989. 22. Moon JB, Jones DL. Motor control of velopharyngeal structures during vowel production. Cleft Palate-Craniofac J. 1991;28:267-273. 23. Moon JB, Smith AE, Folkins JW, Lemke JG, Gartlan M. Coordination of velopharyngeal muscle activity during positioning of the soft palate. Cleft Palate-Craniofac J. 1994; 31:45-55.
THE ROLE OF KNOWLEDGE OF RESULTS IN PERFORMANCE AND LEARNING OF A VOICE 24. Folkins JW. Issues in speech motor control and their relation to the speech of individuals with cleft palate. Cleft Palate J. 1985;22(2):106-122. 25. Austin SE Movement of the velum during speech and singing in classically trained singers. J Voice. 1997;11(2):212-221. 26. Vennard W. Singing: The Mechanism and the Technic. New York, NY: Carl Fischer; 1967. 27. Verdolini-Marston K, Burke MK, Lessac A, Glaze L, Caldwell E. Preliminary study of two methods of treatment for laryngeal nodules. J Voice. 1995;9:74-85. 28. Schmidt RA. Frequent augmented feedback can degrade learning: evidence and interpretations. In: Requin J, Stel-
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mach GE, eds. Tutorials in Motor Neuroscience. Netherlands: Kluwer Academic Publishers; 1991. Lee TD, Maraj BKV. Effects of bandwidth goals and bandwidth knowledge of results on motor learning. Res Q Exer Sport. 1994;65(3):244-249. Wulf G, Lee TD, Schmidt RA. Reducing knowledge of results about relative versus absolute timing: differential effects on learning. JMotorBehav. 1994;26:362-369. House AS, Stevens KN. Analog studies of the nasalization of vowels. J Speech Hearing Disord. 1956;21:218-232. Fant G. Acoustic Theory of Speech Production. The Hague: Mouton; 1960.
Journal of Voice, Vol. 14, No. 2, 2000
Vol. 14, No. 2, pp. 137-145 © 2000 Singular Publishing Group
The Role of Knowledge of Results in Performance and Learning of a Voice Motor Task Kimberly Steinhauer and Judith Preston Grayhack Department of Communication Science and Disorders University of Pittsburgh Pittsburgh, Pennsylvania
Summary: The relationship between the provision of Knowledge of Results and the performance and learning of a voice motor task was examined. Thirty adult subjects, randomly assigned to a 100%, 50%, or No Knowledge of Results group, practiced a novel vowel nasalization task. Measures of accuracy and variability obtained during the practice session indicated influence of knowledge of results schedule on the transient effects of motor performance. Deviations from the nasalance target during the retention phase, 5 minutes later, and during a transfer phase, 24 hours later, indicated influence of knowledge of results schedule on the permanent effects of motor learning. Collective results revealed that an increase in relative frequency of knowledge of results led to a decrease in motor performance and learning of a vowel nasalization task: Both accuracy and variability were degraded as knowledge of results increased, with those subjects in the 100% group exhibiting the poorest scores. Key Words: Knowledge of Results--Practice--Nasalance
Singing teachers and voice therapists deal with improving human performance and facilitating learning through permanent behavioral changes. It is critical to understand how variables such as task and practice impact the acquisition of new motor patterns. This investigation addresses the relationship between a practice strategy using Knowledge of Results (KR) and motor acquisition and retention of a voice motor task, vowel nasalance. The purpose of the study was to determine the effect of manipulating
relative frequency of KR on performance and learning of a vowel nasalization task as measured by a nasalance score. Feedback, sensory information about a movement, remains second in importance only to practice as a variable influencing motor skill acquisition.I, 2 Voice researchers have explored the contribution of auditory feedback to voice motor control, 3 but have been less attentive to the role of extrinsic, augmented feedback in voice motor skill acquisition. 4 Due to the complexity of studying intrinsic feedback, motor learning researchers have concentrated on manipulating variables of extrinsic feedback such as KR. 1,5-10 KR is verbal, or verbalizable, terminal augmented feedback about the outcome or nature of the result in terms of the environmental goal (eg, "The target was 80, your score was
Accepted for publication April 20, 1999. Address correspondence and reprint requests to Kimberly Steinhauer, Department of Communication Science and Disorders, 4033 Forbes Tower, University of Pittsburgh, Pittsburgh, PA 15260 USA Presented at the Twenty-Seventh Annual Symposium: Care of the Professional Voice; June 2, 1998; Philadelphia, PA
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72."). Relative frequency of KR refers to the percentage of trials in which KR is offered. Within the confines of a motor learning experiment, subjects practice on a selected motor task, and then progress is documented as a function of practice trial. Salmoni, Schmidt, and Walter advocated distinguishing between KR effects on performance and KR effects on learning. 1 Performance effects typically measured during the acquisition phase are considered as temporary or transient changes. Learning effects measured during retention and transfer phases are considered as permanent changes. Variables such as motivation and fatigue that accompany the provision of KR during acquisition have been found to contaminate motor learning results; therefore, Salmoni et al 1 suggested measuring motor learning via a retention design in which all groups are treated to a common level of the independent variable, usually no KR, following the acquisition phase. In addition, transfer designs that include a shift of the task or target as a powerful indicator of motor learning were advocated. The most compelling results of studies of motor learning have been those in which retention and transfer tests were administered after the performance effects dissipate d - r a n g i n g from as little as 5 minutes to 5 days, or 5 months postacquisition.1 Theories of motor learning underscore different roles for KR during motor skill learning. Properties of motivation, guidance, and association have been examined as possible explanations for the function of KR during motor learning.l, 2,8 Schmidt's openloop schema theory and guidance hypothesis are founded on movement categories or schemas (ie, ball pitching or pitch elevation) that are governed by a stored, generalized motor program (GMP) containing specific parameters for that action. 2,H Studies conducted within the context of Schmidt's theory showed an inverse relationship between relative frequency of KR and motor learning, regardless of the KR schedule (ie, after alternating trials, after trial block, or faded throughout practice). Increases in relative frequency of KR resulted in degraded learning effects during retention and transfer. 1,12-14 In addition, increases in relative frequency of KR increased motor performance during acquisition; 1 however, other investigations reported that an inJournal of Voice, Vol. 14, No. 2, 2000
crease in relative frequency of KR failed to produce a performance effect during acquisition.12, ~4 The alternative to the prescriptive theory of motor control and learning lies in the dynamical systems approach that describes humans as self-organizing systems capable of movement through an emergent result of changes in coordinative structures governed by underlying physical, synergetic, or ecological principles. 15,16 In the emergent context, motor learning is viewed as the integration of new coordination patterns or synergies on the background of preexisting patterns called intrinsic dynamics. 16-L8 Swinnen suggests that KR acts to either exploit or suppress the learner's intrinsic dynamics during practice. 18 Although KR has been used to describe the "to be learned" pattern, ~9 specific predictions about the frequency of KR have not been addressed due to the recent incorporation of motor learning into the dynamical theories of motor control. Regardless of the theoretical genesis, many studies have documented relationships between limb motor learning and relative frequency of KR; 20 however, few investigations have examined the impact of practice with KR on voice production. Ferrand explored the relationship between KR and phonatory stability, as indexed by jitter and shimmer. 4 Two groups of subjects practiced sustaining a n / a / f o r 2 seconds. The KR group received information on every trial about the waveform and jitter/shimmer values. A second group received no KR. Results of the transfer session, held 1 week after practice, revealed no difference between groups for either shimmer or jitter measurements, indicating no relationship between providing KR and permanent changes in phonatory stability. The disparate results within the limb and voice KR literature motivated this research project designed to determine the influence of KR on learning a voice motor task integral to optimal voice resonance. The percept nasality is modulated to some degree by varying the size of the velopharyngeal port, as well as the entire oral cavity. Volitional modification of nasality is a common goal among singers and speakers across most voice quality productions but novel to voice producers when practiced in isolation, thus providing a unique task upon which to test voice motor learning.
THE ROLE OF KNOWLEDGE OF RESULTS IN PERFORMANCE AND LEARNING OF A VOICE Although proprioceptive innervation of the velopharyngeal sphincter is limited, 21 volitional control of nasality has been documented.22, 23 Moon and Jones demonstrated dynamical properties of the velopharynx through a study in which 10 subjects successfully produced b o t h / a / a n d / i / a t 50% and 75% nasality using simultaneous phototransduction to provide visual feedback. 22 Results showed that success at achieving the target was attributable to plasticity (learning) or flexibility (success without learning), two mechanisms of dynamical motor learning described by Folkins. 24 Plasticity referred to a restructuring of the physiological rule system that occurs during practice. Flexibility referred to an existing rule system confined to parameters of the coordinative structure that accounts for success at a novel task without practice. In singing instruction,25, 26 cleft palate rehabilitation, 22 and resonant voice therapy 27 clients are asked to exploit nasality to alter articulation and resonance properties of the vocal tract. Therefore, the aim of this study was to test the effects of manipulating the relative frequency of KR (100%, 50%, and no KR) during learning of a vowel nasalization task, as estimated by nasalance score. Results from the study will be interpreted within the context of Schmidt's 11 schema theory predicting differential effects of KR on performance and learning and Folkin's 24 theory predicting a possibility of no effect of KR on performance and learning due to the dynamical properties of coordinative structures.
METHODS Subjects Thirty subjects (20 women, 10 men) between the ages of 18 and 40 years were selected from the student population at the University of Pittsburgh for the study. All subjects were required to have a negative history for speech deficits, and to pass a hearing screening at 20 dB SPL. The racial, gender, and ethnic characteristics of the proposed subject population reflected the demographics of Pittsburgh and the surrounding area. Subjects were required to test within nasalance norms for the Zoo Passage as measured by the Kay Elemetrics Nasometer. All subjects were native speakers of English and vocally untrained, that is,
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had participated in less than five private speaking/singing lessons. The subjects were healthy nonsmokers, experiencing no upper respiratory or sinus infections, and free of alcohol and medications that have the potential to compromise normal voice motor control. The subjects remained naive to the specific purposes of the experiment, had no previous exposure to the experimental vocal task, and were not significantly different in their baseline performance of the task.
Apparatus The Kay Elemetrics Nasometer, a computer-assisted instrument, facilitated measurement of nasalance over time. The Nasometer is a noninvasive input device consisting of two directional microphones and a sound separator plate. The calculated nasalance score is a ratio of nasal to oral plus nasal acoustic energy for each subject. KR as nasalance score appeared on the computer monitor. The dynamic range of the Nasometer is 50 dB, thus ensuring accurate data collection on a wide range of voice intensities. Task
Acquisition~Retention The subjects were required to nasalize a sustained vowel ( / i / - - > / t / ) . To ensure stable and volitional control, each trial was 6 seconds in duration--2 seconds of oral phonation before switching to nasal for the final 4 seconds. Target nasalance score for the oral vowel was between 0% and 40%, and the target score for the nasalized vowel was 80%. Subjects proceeded with the task only after achieving the initial target for the oral vowel. Transfer The transfer task required the subjects to perform the identical task Using a new vowel,/a/.
Experimental design and procedure Acquisition Thirty subjects were assigned randomly to three groups of feedback (100% KR, 50% KR, No KR). KR as percent nasalance was administered to the subjects via a computer monitor. Subjects in the 100% KR group received immediate information afJournal of Voice, Vol. 14, No. 2, 2000
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KIMBERLY STEINHAUER AND JUDITH PRESTON GRAYHACK
ter every trial. The 50% KR group received immediate information after every other trial. The No KR group was not permitted to view the monitor. During initiation of the session, the experimenter provided instructions and demonstrations involving the task and apparatus. Using the nasometer, subjects practiced on four trials using a different vowel, /if, and a different nasalance target, 65%. All subjects received information in the form of nasalance score and received a countdown to prepare, initiate, and change the vocalization. Motor performance was examined during the acquisition phase consisting of 5 blocks of 8 trials. All subjects filled the 2second intertrial interval with counting by twos or threes in order to control for mental rehearsing. Retention~transfer
Learning was examined during a retention and transfer phase in which all subjects moved to a common level of the independent variable, No KR. The immediate retention phase, 5 minutes following acquisition, consisted of 2 blocks of 8 trials using the identical task. The transfer phase, 1 day after acquisition, consisted of 2 blocks of 8 trials using the transfer vowel/a/.
Data collection and statistical considerations The effect of the independent variable, KR relative frequency, was measured using the dependent variable, nasalance score. The central 2 seconds of the total nasal utterance (4 seconds in duration) were used for analysis to ensure stability of the target nasalized vowel. Performance effects were measured during the acquisition phase, and learning effects were measured during retention and transfer phases. Three dependent measures sensitive to changes in accuracy and variability 2 were calculated. Absolute error (AE) is the average absolute deviation between the subject's responses and the target:
AE - i=l
Ixi- sl rt
Absolute constant error (/CE/) is the average error in responding to the target and represents the accura-
Journal of Voice, Vol. 14, No. 2, 2000
cy and bias in the directional measures of average magnitude of response:
•
(x i - T) / C E / = i=l _ 12
Variable error (VE) is the variability of the subject about the mean response and is a measure of intraindividual response consistency:
VE =
t
~
i=1
(Xi _ .~)2
The acquisition data were analyzed in a 3 × 5 (Group × Block) ANOVA with repeated measures on the last factor. For both retention and transfer tests, the 16 trials were collapsed into one block and analyzed in univariate ANOVAs (group as the independent variable). Alpha was set at the .05 level, and appropriate post hoc tests were performed to elicit specific group or block differences.
RESULTS Group mean and standard deviation data for the dependent measures are listed in Table 1. The dependent measures as a function of trial block on a performance curve depict group differences in Figure 1 (/CE/), and Figure 2 (VE). The Pearson product moment correlation for accuracy measures AE and /CE/, r = .98, indicated that the measures were redundant; therefore, o n l y / C E / i s reported as a measure of accuracy and bias that is independent of V E ) 2 One outlier with scores consistently 2 standard deviations from the mean was discarded from the No KR group.
Acquisition Results for the/CE/analysis showed a significant group difference F(2,104 ) = 4.70, P<.05 (Figure 1). Post hoc Student-Newman-Keuls multiple comparisons revealed significant differences between 100% KR (M = 14.08, SD = 15.18) and 50% KR (M = 4.96, SD = 4.09), and between 100% and no KR (M = 6.19, SD = 5.21) groups, P<.05. There were no
THE ROLE OF KNOWLEDGE OF RESULTS I N PERFORMANCE AND LEARNING O F A VOICE
141
T A B L E 1. Group Means and Standard Deviatons in %
Nasalance for Feedback Group Acquisition
Retention
Transfer
100% KR /CE/
14.08 (15.18)*
8.61 (6.58)
25.20 (16.82)*
VE
7.70 (6.76)
7.10 (4.90)*
6.94 (4.04)
/CE/
4.96 (4.09)*
5.63 (4.15)
12.20 (5.64)*
VE
5.77 (5.81)
3.80 (2.40)*
6.13 (3.48)
/CE/
6.19 (5.21)*
6.19 (5.21)
14.57 (7.55)
VE
5.29 (5.54)
3.60 (0.70)*
6.95 (6.89)
50% KR
No KR
Mean (Standard Deviation) *P <.05
/CE/ 30 25
~
20
¢
N o KR
,,~ 15
--m-- 50% KR
~
~100%KR
10 5 0 0
I 1
t 2
I 3
I 4
I 5
I
I ret
I trans
Block
F I G 1. Group mean five-block absolute constant error (/CE/) scores in % nasalance for acquisition (Block 1-5), retention (ret), and transfer (trans).
VE
12 10
tU >
8
;
N o KR
6
--
50% KR 100% KR
4 2 0 0
I 1
I 2
I 3
I 4
I 5
I
I ret
I trans
Block
F I G 2. Group mean five-block variable error (VE) scores in % nasalance for acquisition (Block 1-5), retention (ret), and transfer (trans).
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K I MB E R LY STEINHAUER AND JUDITH PRESTON GRAYHACK
other main effects or interactions. The group differences in/CE/indicate that accuracy to the nasalance target was enhanced by decreasing the relative frequency or withholding KR, with 100% KR leading to detrimental decreases in accuracy. Results for the VE analysis showed significant block differences across KR conditions in the acquisition phase, F(4,104 ) = 2.62, P<.05 (Figure 2). Post hoc Student-Newman-Keuls multiple comparisons revealed significant differences between Block 1 (100% K R M = 11.09, SD = 8.27; 50% KR M = 7.17, SD = 6.27; No KR M = 8.03, SD = 9.19) and Block 5, (100% KR M = 6.51, SD = 3.75; 50% KR M = 3.50, SD = 1.21; No KR M = 3.68, SD = 1.63), P<05. There were no other main effects or interactions. The block difference in VE indicates that variability about the subject's nasalance mean was decreased by practice from Block 1 to Block 5. Retention Differences in /CE/ measures were not great enough to elicit significant results; however, results for the VE analysis showed significant feedback differences in the retention phase, F(2,26) = 3.62, P<.05 (Figure 3). Post hoc Dunnett's multiple comparisons revealed significant differences between 100% KR ( M = 7.10, SD = 4.90) and 50% KR ( M = 3.80, SD = 2.40) and between 100% KR and no KR (M = 3.60, SD = .70) groups, P<.05. The group differences in VE indicate that variability about the subject's nasalance mean was reduced by decreasing the relative frequency or withholding KR, with 100% KR leading to detrimental increases in variability. Transfer Results of the/CE/analysis indicated significant group differences for the Transfer phase F(2,26/ -4.06, P<.05 (Figure 2). Post hoc Student-NewmanKeuls multiple comparisons revealed significant differences between 100% KR (M = 25.2, SD = 16.82) and 50% KR (M = 12.2, SD = 5.64) groups, P<.05. The group differences for/CE/indicate that accuracy to the nasalance target was enhanced by decreasing the relative frequency or withholding KR, with 100% KR leading to detrimental decreases in accuracy. No significant differences were observed for VE measures. Journal of Voice, Vol. 14, No. 2, 2000
DISCUSSION The aim of the present study was to explore the effect of relative frequency of KR on the motor performance and learning of a vowel nasalization task. The results showed that an increase in relative frequency of KR led to a decrease in both motor performance and learning of a vowel nasalization task; however, the results revealed a curious departure from the limb motor learning literature in that No KR proved as beneficial as 50% KR. The group differences in target accuracy (/CE/) during the acquisition phase indicate that temporary effects of motor performance were enhanced by decreasing the relative frequency to 50% or withholding KR, with 100% KR leading to detrimental decreases in motor performance of a vowel nasalization task. These results are inconsistent with past studies testing Schmidt's schema theory ~ that predict increased motor performance with increased KR; however, the results of this study are consistent with more recent studies in which increased KR decreased or exhibited no effect on motor performance.12,14 Similar group differences in target accuracy (/CE/) were observed in the transfer phase, indicating that permanent effects of motor learning were enhanced by decreasing the relative frequency to 50% KR, with 100% KR leading to detrimental decreases in motor learning of a vowel nasalization task. These results are consistent with Schmidt's schema theory 11 (and collaborative studies) that predict increased motor learning with decreased relative frequency of KR.1,12-14,20
Results of the variability measure (VE) exhibited a different pattern for acquisition and retention. The block difference between Block 1 and Block 5 during acquisition reveals that practice, not amount of KR, was the most important indicator for reducing variability during motor performance of a vowel nasalization task. The group difference during retention reveals that amount of KR was the most important indicator for reducing variability in motor learning: Decreasing the relative frequency to 50% or withholding KR enhanced motor learning, with 100% KR leading to detrimental decreases in motor learning of a vowel nasalization task.
THE ROLE OF KNOWLEDGE OF RESULTS IN PERFORMANCE AND LEARNING OF A VOICE
Often overlooked in favor of accuracy measures, reductions in variability are of paramount importance as indicators of enhanced subject stability, thus motor learning.Z, 19 All subjects in this study became more consistent with practice during acquisition, but during retention, an indicator of motor learning, those subjects who received 50% or no KR were more consistent than subjects receiving 100% KR. As stated previously in the discussion of accuracy during transfer, the variability results of this study are consistent with those conducted within the context of Schmidt's schema theory of motor learning.11 The following explanations for the present result, that 100% KR degrades both accuracy and variability of motor performance and learning, have been postulated:2°,29, 30 (1) KR may become so integrated into the task that performance may be disrupted when KR is withdrawn. (2) Increased KR as extrinsic feedback may prevent subjects from attending to their own intrinsic feedback. Subjects may overfacilitate planning of the next movement and negate engaging in self-generated retrieval operations. (3) A high-frequency KR schedule may lead subjects to produce excessive response variability during practice or maladaptive short-term corrections, thus preventing the development of a stable movement representation or motor program. Maladaptive corrections occur in situations where the motor system is successful at obtaining the target but not capable of exact precision due to neuromuscular variability. Perhaps the target of 80% nasalance was too precise for the subjects to master, and a range of 75% to 85% nasalance would have been more accessible. The maladaptive correction theory could also explain why the jitter and shimmer values in Ferrand remained unresponsive to differences in the provision of KR. 4 Although findings that 100% KR leads to decreased motor learning are common, 20 less common are results similar to the present study in which a group receiving No KR performed as well as a group receiving information. Results of accuracy measures in acquisition (Figure 1) and variability measures during retention (Figure 2) reveal that groups receiving 50% and No KR performed similarly. An explanation for the similarity of 50% and No KR groups lies in dynamical theories of motor con-
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trol. 15,24 Moon and Jones reported evidence of suc-
cess without learning as subjects achieved the novel task of velopharyngeal closure on first attempts. 22 In the context of Folkins, 24 they attributed this success as compatible with the function of forced-variation flexibility during motor learning involving coordinative structures. Folkins contends "when a rule system is set up through a coordinative structure, it is not necessary to go through an adaptation process to find novel solutions fitting the coordinative structure."24(pl12) In the present study, it is possible that the target of 80% lies in the optimal range of nasalance for the production of the vowel / 7/, rendering KR futile for successful completion of the task; however, too much information, as in the case of 100% KR, was so powerful that it interfered with the optimal movement of the nasalization coordinative structure during both performance and learning phases. Similar results were obtained during experiments in which subjects were provided with erroneous KR that overrode correct sensory feedback to diminish target accuracy. 6 Remaining in the dynamical context, it is possible to explain the decreased accuracy and increased variability of producing the v o w e l / a / a t 80% nasalance during the transfer phase (Figure 1). Moon and Jones reported that the v o w e l / a / w a s more accurately produced at 50% closure than the vowel/i/. 22 Although the acoustic nasalance score is once removed from closure percents of phototransduction, it appears as if the vowel/a/is more optimally nasalized at a lower percent than the vowel/i/. These results also are consistent with acoustic and perceptual data showing characteristic patterns of nasality on the basis of tongue height for the v o w e l s / i / a n d / a / ) ~,32 Due to tongue height, the nasalization o f / i / r e q u i r e d less coupling with the nasal cavity than that required for a nasalized production of the vowel/a/. Finally, a second explanation for the similar behavior of the No KR to the 50% K R group lies in methodological limitations of the study. The sample could have been too small to elicit the group differences. It is possible that auditory feedback provided enough information to guide the learners to the correct target; however, control of the auditory feedback loop was maintained by using only those subjects who did not receive formal voice or singing training.
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Also although group assignment was randomized, it is possible that the more proficient subjects were assigned to the No KR and 50% KR groups.
CONCLUSIONS Collective results indicate a relationship between relative frequency of KR and motor performance and learning of a vowel nasalization task. An increase in relative frequency of KR to 100% degraded both motor performance and learning as indexed by accuracy and variability measures. In acquisition, retention, and transfer, both accuracy (/CE/) and variability (VE) diminished as KR increased, with 100% KR groups exhibiting the poorest scores; however, there were minimal or no differences between groups receiving 50% or No KR. The detrimental effects of providing a high frequency of KR have been documented and are consistent within the context of Schmidt's schema theory.20, % Success at executing a voice motor goal with minimal or no KR has been documented and is consistent within the context of dynamical systems theory.22, 24 Further study incorporating auditory masking of trained and untrained subjects could provide additional evidence for the power of KR during voice motor skill acquisition. Also, future research to more discretely examine the theoretical issues of the prescriptive and dynamical systems as they pertain to KR and voice motor control is warranted.
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7. Feltz DL, Landers DM, Becker BJ. A revised meta-analysis of the mental practice literature on motor skill learning. In: Druckman D, Swet J, eds. Enhancing Human Performance: Issues, Theories, and Techniques. Washington, DC: National Academy Press; 1988:61-101. 8. Lee TD, Swinnen SR Serrien DJ. Cognitive effort and motor learning. Quest. 1994;46:328-344. 9. Lee TD, White MA, Carnahan H. On the role of knowledge of results in motor learning: exploring the guidance hypothesis. J Motor Behav. 1990;22:191-208. 10. Wulf G, Horstmann G, Choi B. Does mental practice work like physical practice without information feedback? Res Q Exerc Sport. 1995;66:262-267. 11. Schmidt RA. A schema theory of discrete motor skill learning. Psychol Rev. 1975;82(4):225-260. 12. Winstein CJ, Schmidt RA. Reduced frequency of knowledge of results enhances motor skill learning. J Exp Psychol. 1990;16:677-691. 13. Wulf G. The learning of generalized motor programs and motor schemata: Effects of KR relative frequency and contextual interference. J Hum Movement Stud. 1992;23: 53-76. 14. Wulf G, Schmidt RA. The learning of generalized motor programs: Reducing the relative frequency of knowledge of results enhances memory. J Exp Psychol. 1989;15:748757. 15. Kelso JA, Tuller B. A dynamical basis for action systems. In: Gazzaniga M, ed. Handbook of Cognitive Neuroscience. New York, NY: Plenum Press; 1984:321-356. 16. Wallace SA. Dynamic pattern perspective of rhythmic movement: an introduction. In: Zelaznik HN, ed. Advances in Motor Learning and Control. Champaign, Ill: Human Kinetics; 1996:155-194. 17. Newell KM. Motor skill acquisition. Ann Rev Psychol. 1991;42:213-237. 18. Swinnen SR Information feedback for motor skill learning: a review. In: Zelaznik HN, ed. Advances in Motor Learning and Control. Champaign, Ill: Human Kinetics; 1996:37-66. 19. Schoner G, Zanone PG, Kelso JAS. Learning as change of coordination dynamics: Theory and experiment. J Motor Behav. 1992;24:29-48. 20. Schmidt RA, Bjork RA. New conceptualizations of practice: Common principles in three paradigms suggest new concepts for training. Psychol Sci. 1992;3(4):207-217. 21. Kuehn DR Lemme ML, Banmgartner JM. Neural Bases of Speech, Hearing and Language. Boston, Mass: CollegeHill Press; 1989. 22. Moon JB, Jones DL. Motor control of velopharyngeal structures during vowel production. Cleft Palate-Craniofac J. 1991;28:267-273. 23. Moon JB, Smith AE, Folkins JW, Lemke JG, Gartlan M. Coordination of velopharyngeal muscle activity during positioning of the soft palate. Cleft Palate-Craniofac J. 1994; 31:45-55.
THE ROLE OF KNOWLEDGE OF RESULTS IN PERFORMANCE AND LEARNING OF A VOICE 24. Folkins JW. Issues in speech motor control and their relation to the speech of individuals with cleft palate. Cleft Palate J. 1985;22(2):106-122. 25. Austin SE Movement of the velum during speech and singing in classically trained singers. J Voice. 1997;11(2):212-221. 26. Vennard W. Singing: The Mechanism and the Technic. New York, NY: Carl Fischer; 1967. 27. Verdolini-Marston K, Burke MK, Lessac A, Glaze L, Caldwell E. Preliminary study of two methods of treatment for laryngeal nodules. J Voice. 1995;9:74-85. 28. Schmidt RA. Frequent augmented feedback can degrade learning: evidence and interpretations. In: Requin J, Stel-
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