APPLIED COGNITIVE PSYCHOLOGY, VOL. 1,273-283 (1987)

Kinematic Information Feedback and Task Constraints

K. M. NEWELL, J. T. QUINN and M. J. CARLTON University of Illinois at Urbana-Champaign

SUMMARY

The experiments were designed to examine the effect of task constraints on the influence of kinematic information feedback to facilitate the acquisition of discrete arm movements. The findings of Experiments 1 and 3 revealed that when the criterion kinematic trajectory was an increasing acceleration function, the most effective control space representation for kinematic feedback (is. position-time; velocity-position) was the one that matched the error criterion t o be minimized. Furthermore, in Experiment 1 the velocity-position feedback condition led to greater performance error than the discrete knowledge of results of movement time or integrated position-time error. Experiment 2 showed that kinematic information feedback of the movement trajectory (position-time; velocity-position) did not facilitate acquisition of a constant velocity criterion, in contrast to knowledge of results of movement time or integrated velocity-position error. Collectively the findings suggest that the interaction of task and organismic constraints dictates the nature of the information feedback required to facilitate the acquisition of skill. The augmented information available must match the degrees of freedom requiring constraint in the movement sequence.

In a recent series of experiments we have contrasted the effect of kinematic information feedback with knowledge of results (KR) in the acquisition of discrete single biomechanical degree of freedom tasks (see Newell and Walter, 1981; Newell and McGinnis, 1985; Newell, Morris and Scully, 1985, for reviews of this work). These experiments have clearly shown that kinematic information feedback can facilitate performance beyond the level achieved through traditional KR information (see also Hatze, 1976; Howell, 1956). On the basis of these experimental findings we have developed a framework for the application of augmented kinematic information feedback utilizing topological dynamics (McGinnis and Newell, 1982) to describe both movement and the constraints imposed upon movement. The general principle advanced by Newell and McGinnis (1985), and explored in this paper experimentally, is that augmented kinematic information feedback must be presented to the subject in terms of the control space that is required to define unequivocally task constraints, together with the constraints imposed upon movement by optimization criteria.

Essential to the application of topological dynamics is an understanding of the kinematic constraints imposed by task criteria. Kinematic information relates to the space-time properties of movement, and examples include the displacement velocity and acceleration of body and limb motion. These criteria can be framed explicitly, in terms of the goal of the task, or implicitly, in terms of the various physical constraints inherent in the interaction of the organism and environment. For example, in a recent set of experiments on kinematic information feedback (Newell, Walter, Quinn and Sparrow, 1983), it was shown that a continuous kinematic representation of the 0888-4080/87/040273-1 lS05.50 0 1987 by John Wiley & Sons, Ltd.

Received 20 August 1986 Revised 20 April 1987

214 K . M . Newell et al.

response output only facilitated performance over the level achieved by KR informa- tion in the situation where the task constraint explicitly required the acquisition of a given kinematic trajectory. Similar findings were observed in tests of these principles with kinetic information feedback in the acquisition of isometric tasks (Newell, Sparrow and Quinn, 1985b). These findings are consistent with the proposal of Fowler and Turvey (1978) that the augmented information available to the subject must match the degrees of freedom requiring constraint in the movement sequence.

The experiments reported here advance beyond a demonstration of the advantage of kinematic information feedback over KR to explore the ways in which task constraints dictate the use of the appropriate control space to both prescribe and describe the movement sequence. Different control spaces utilize different kinematic parameters to describe motion. For example, in configuration space only spatial coordinates are invoked to describe the motion of the limb. In event space a time dimension is added to the configuration space so that positional changes of the limb may be represented with respect to time. In state space the state of a body point is defined by the position and velocity coordinates of that point at some time. The key issue about the different control space representations from the perspective of their application to augmented feedback is that while all spaces may be used to describe a given movement trajectory, they are not all sufficient to unambiguously define the criterion trajectory or actual limb trajectory in space-time (see McGinnis and Newell, 1982; Newell and McGinnis, 1985, for reviews of the application of topological dynamics to information feedback and skill acquisition).

In the experiments reported here, task constraints were manipulated across experiments by varying the task criterion for a single degree of freedom movement. Some movement parameters were held constant across experiments to facilitate comparison of the findings. A change of task constraints can also lead to an interaction with organismic constraints in that subjects have prior knowledge of certain response configurations and not others. Collectively, the findings from the current experiments suggest that the interaction of task and organismic constraints dictates the appropriate control space representation of augmented kinematic information feedback to facilitate the acquisition of skill.

EXPERIMENT 1

In this experiment the criterion discrete movement required the generation of a specific acceleration constant through a defined range of movement. Augmented information feedback was presented to the subject in the acquisition trials in one of four different ways: (1) movement time KR; (2) absolute integrated position-time error with respect to the criterion position-time function; (3) a position-time graphic representation of the actual trajectory superimposed on the criterion position-time trajectory; (4) a velocity-position graphic representation of the actual trajectory superimposed on the criterion velocity-position trajectory.

It was anticipated that as minimization of the absolute integrated position-time error was the task criterion, the least error after practice with augmented feedback would be achieved by the position-time graphic kinematic information group, as this is the only condition to provide all the information necessary to minimize error. The velocity-position control space representation provides a continuous representation of

Kinematic Information Feedback 275

the movement but it is potentially ambiguous with respect to the timing elements of the response. Therefore, in contrast to the position-time representation, the information provided to the subject in the velocity-position condition may not be adequate to optimize learning, in spite of the fact that it provides a continuous representation of movement. These two continuous kinematic conditions were contrasted with the two discrete information conditions. It was anticipated that the latter two conditions would facilitate performance the least, because they provide less information than the continuous representations to define unambiguously response output relative to the task constraints. After 75 feedback trials the augmented information feedback was withdrawn to examine feedback withdrawal effects (Salmoni, Schmidt and Walter, 1984). Previous kinematic and kinetic information feedback experiments (Newel1 et al., 1983, 1985) have shown no immediate performance deterioration when feedback was withdrawn, but a feedback withdrawal phase was included to provide additional tests of kinematic information feedback withdrawal, as these are sometimes important in practical settings.

Method

Subjects The subjects were 44 naturally right-handed student volunteers (22 males, 22 females) from the University of Illinois. Subjects were not paid for their services.

Apparatus The apparatus consisted of a horizontal displacement bar formed by a steel bar 75 cm in length that extended horizontally from its axis of rotation. Attached to the distal end of the bar was a 46 cm long handle which could be adjusted to accommodate different arm lengths. The bar was free-moving through a range of 180 degrees. Mounted at the axis of rotation of the bar was a Bournes 10 turn 50 K potentiometer. Attached to the distal portion of the bar 44 cm from its axis of rotation was an accelerometer. The entire system was mounted on a 1.2 cm aluminium backing sheet supported by a scaffolding system. Thus, the system required the subject to produce horizontal flexion movements of the right shoulder and arm (see Carlton, 1983, for a further description).

Positioned below the apparatus was a large adjustable armchair that could be adapted for the height of the subject. Each subject was positioned so that the axis of rotation and the bar was directly over the subject’s right shoulder. Two large white poles mounted on wooden bases were used to designate the target position. The complete system was controlled by a PDP 11/73 Dec/Lab computer which was used both to control the experiment and to collect and store information related to each movement. All movement data were collected at a sampling rate of 1000 Hz. In addition, a Tektronix 4010 graphic terminal was used to display movement information to the appropriate groups following each trial.

Procedures Subjects participated in a single testing session during which they performed movements of horizontal displacement of the right arm under one of four different feedback conditions. The subject’s task was to learn to move the bar through two designated target positions at a constant rate of acceleration (2.22 x deg/ms/ms).

276 K . M. Newell et al.

They were informed by the instructions and a graphic representation that the task criterion required the minimization of the absolute integrated error of the position-time trace from the criterion position-time trajectory. Following each trial the subject was provided augmented information feedback relative to the assigned feedback condition. The four information feedback conditions included: (1) movement time (ms) presented orally by the experimenter; (2) absolute integrated error presented orally by the experimenter; (3) computer-generated template position-time trace superimposed on the position-time representation of the just-produced trial; (4) template velocity-position trace superimposed on the velocity-position representation of the just-produced trial. The two graphic feedback conditions reflect, respectively, event space and state space representations of the template and just-produced response (McGinnis and NeweH, 1982). The feedback information in each condition was presented 10 s after each response. In the computer-assisted feedback conditions the kinematic representation was available to the subject for 5 s. The intertrial interval was 20 s.

Each trial began with a warning in the form of an oral ‘ready’ response from the experimenter followed 1-2 s later by an oral ‘start’ response. All subjects completed 75 feedback trials followed immediately by 25 no-feedback trials for a total of 100 trials. Subjects were randomly assigned to one of the four augmented-feedback groups. Sex of the subject was counterbalanced between groups.

Results and discussion

The primary dependent variable was absolute integrated error of the difference between the template and the just-produced position-time trace, as this was the parameter that subjects were instructed to minimize. Figure 1 displays the mean

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Kinematic Information Feedback 277

absolute integrated error in blocks of five trials over the feedback and no-feedback trials for each information feedback condition. The information feedback effect was significant, F (3,40) = 6.78, p c .05. The mean absolute integrated error (deg/ms) for each group was: movement time ( M = 8.03), verbal absolute integrated error (M = 9.22), position-time (M = 5.67) and velocity-position ( M = 10.97). Post-hoc analysis revealed that the graphic position-time condition produced significantly less error than the oral absolute integrated error and the graphic velocity-position conditions (p values < .01) and the movement time condition (p < .05), while the movement time condition also produced significantly less error than the velocity-position condition (p < .05). These group differences appear small on an absolute basis but are considerable for learning strategy effects when considered on a relative basis.

The trial blocks effect was significant, F (14,560) = 6.72, p < .01. The main effects for practice and information feedback need to be interpreted in light of a significant trial blocks by feedback interaction, F (42,560) = 1.77, p -= .01. Figure 1 indicates that the velocity-position feedback condition did not reduce error over the practice trials whereas all other groups did. Furthermore, the overall group effects are due to differences that emerge over the practice trials.

The augmented feedback group differences evident on the last practice block with feedback were maintained over the feedback withdrawal trials, F (3, 40) = 18.25, p < .05. There was no significant effect for trial blocks over the feedback withdrawal trials, F (4, 160) = 1.04, p > .05. The groups by trial blocks interaction also was non- significant ( F < 1).

EXPERIMENT 2

In this experiment the task constraints were changed so that the criterion was a constant velocity in a certain phase of the discrete movement. This is a criterion that is more familiar to adult subjects than a constant positive acceleration and, as a consequence, the impact of augmented information conditions may be different from that found in Experiment 1. First, the velocity-position control space representation of the just- completed movement may be as appropriate information for the subject as the position-time function, as it now provides information explicitly in terms of the task goal. Second, if subjects can perceive constant velocity of their own limb movements, then even KR of movement time may be sufficient information for subjects to optimize performance. With distance fixed, constant velocity (if achieved) covaries with movement time. In summary, a different pattern of performance relationships was expected between the augmented-feedback groups than shown in Experiment 1 due to the change in task constraints. It is possible that the discrete KR feedback conditions may be sufficient to optimize performance with a constant velocity criterion. To facilitate comparison between experiments, the criterion movement time of 300 ms and a 30 degree range of motion were preserved. The number of trials was also increased in this between-day retention period on the initial KR and subsequent no-KR trials of day 2. This manipulation was made in part to examine the contention of Salmoni et al. (1984) that the influence of KR has a temporary performance effect rather than a more permanent learning effect.

218 K . M . Newel1 et al.

Method

Subjects The subjects were an additional 48 naturally right-handed adult subjects from the University of Illinois community. An equal number of male and female subjects were assigned to each of the four information feedback groups.

Apparatus and procedures The apparatus and procedures were essentially the same as those reported for Experiment 1. The only change was that the task criterion was now a constant velocity through the 30 degree range of motion with a movement time of 300 ms. The primary error measure was the absolute integrated error between the criterion and actual velocity-position traces. In addition, each subject completed 125 trials with feedback followed by 25 trials of feedback withdrawal over 2 days of practice. On Day 1, subjects completed 75 feedback trials. On Day 2, 50 feedback trials were followed by 25 feedback withdrawal trials.

Results and discussion

Figure 2 displays the mean absolute integrated error (deg/ms) in blocks of five trials over the feedback and no-feedback trials for each information feedback condition. Over the 125 acquisition trials there was no difference between information feedback groups, F (3,44) < 1. There was a general reduction in error over the practice trials, F (24,1056) = 14.66, p < .01, although all the performance gains occurred in the initial 15

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Kinematic Information Feedback 279

trials. The feedback condition by trial blocks interaction was non-significant, F (72, 1056) = 1.06, p < .05. Performance deteriorated somewhat over the feedback withdrawal trials but there was no significant effect for feedback condition, F (3,44) = 1.53, p < .05, trial blocks, F (4, 176) = 2.07, p < .05, or their interaction, F (12, 176) < 1.

EXPERIMENT 3

In this experiment the trajectory of the to-be-produced movement was the same as in Experiment 1, but the criterion was now the minimization of absolute integrated velocity-position error. This criterion was utilized in anticipation that it would produce findings opposite to those of Experiment 1 and, as a consequence, provide converging evidence for the significance of task constraints in specifying the appropriate representation of kinematic information feedback. Only two kinematic information groups were examined over the feedback and feedback withdrawal trials. One group received position-time information of the just-produced response along with the position-time criterion template. A second group received velocity-position informa- tion feedback superimposed on the criterion velocity-position template.

Method

Subjects The subjects were 22 naturally right-handed adults from the University of Illinois community who had not participated in the previous experiments. Thewe was an equal number of males and females in each group.

Apparatus and procedures The apparatus and procedures were identical to those reported for Experiment 1, except for the following changes. The trajectory of the to-be-produced movement was the same acceleration function as that reported for Experiment 1, but the error to be minimized was now the absolute integrated error of the just-produced velocity- position trace rather than the criterion position-time trace used in Experiment 1. There were 75 feedback trials followed by 25 feedback withdrawal trials.

Results and discussion

Figure 3 displays the mean absolute integrated velocity-position error (deg/ms) in blocks of five trials over the feedback and feedback withdrawal trials for each information feedback condition. There was a significant feedback effect, F (1, 20) = 5.44, p < .05, with the velocity-position condition (M = 4.61) having less error than the position-time condition (M = 6.44). The trial blocks effect, F (19, 380) = 7.44, p < .01 and the feedback by blocks interaction, F (19, 380) = 2.07, p < .01, were both significant. This interaction was primarily due to there not being a group effect on blocks 2 and 6, and appears to hold no particular theoretical significance.

The feedback group differences were essentially maintained over the feedback withdrawal trials, although there was a general performance deterioration, F (4, 80)

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practice trials (Experiment 3).

= 3.59, p < .01. The feedback condition by trial blocks interaction was not significant, F (4, 80) = 1.61, p > .05.

GENERAL DISCUSSION

The findings of the three experiments suggest that the interaction of task and organismic constraints dictates the nature of the information feedback required to facilitate the acquisition of skill. Thus the impact of a specific information feedback representation (e.g. KR versus continuous kinematic information) is not absolute, but relative to the constraints imposed upon the performer. It appears that constraints not only determine the optimal function for coordination and control (Kugler, Kelso and Turvey, 1980,1982; Newell, 1986), but, in addition, specify the information (natural and augmented) required by the performer to learn a given activity.

The findings of Experiment 1 confirmed that a continuous presentation of kinematic information feedback in the form of a position-time trace facilitated performance over a discrete KR parameter such as movement time or integrated error. However, the performance of the velocity-position condition in this experiment also revealed that the issue in augmented feedback is not continuous versus discrete information. The constant acceleration function with a position-time error criterion rendered the velocity-position representation ambiguous with respect to the timing elements of the response. Time is explicit in the position-time control space, and this condition generated the best performance among the feedback conditions utilized in Experiment 1. The relative impact of the feedback conditions did not emerge, however, until the subjects had received a number of trials of practice.

Experiment 3 showed that a change in the error to be minimized also alters the potency of a given information feedback representation. Thus the velocity-position

Kinematic Information Feedback 28 1

criterion reversed the relative impact of the two kinematic control space represen- tations found in Experiment 1. This comparison of the findings between Experiments 1 and 3 provides converging evidence of the differential effect of varying task constraints on the impact of augmented kinematic information feedback.

Changing the trajectory to be learned from a constant acceleration function to a constant velocity criterion also influenced the relative effects of the information feedback conditions on skill learning. The failure to find feedback condition effects with a constant velocity criterion suggests several features were operating in this experiment. First, it appears that the discrete parameters of movement time and absolute integrated error provided the information necessary to learn the task. This implies that subjects have a reasonable perception of constant velocity of their own limb movements (although see Runeson, 1974), leaving movement time to be sufficient information to learn the task. If subjects can perceive and produce a constant movement velocity, then the movement time that emerges correlates directly with average, and in this case constant, velocity. In this view movement time is sufficient to optimize performance based upon the prior knowledge of subjects regarding constant velocity. This finding suggests that organismic constraints in the form of prior knowledge interact with task constraints in determining the optimal augmented information feedback.

The general maintenance of performance during the feedback withdrawal trials in all three experiments suggests that the feedback techniques employed provided more than temporary support for the learner (Salmoni et al., 1984). Performance did deteriorate somewhat during the feedback withdrawal trials of Experiment 3, but this effect was common across the feedback groups utilized. It seems, therefore, that kinematic information feedback operates similarly to traditional KR in that the sustaining of performance level during the feedback withdrawal phase is intimately linked to the number of initial practice trials with feedback (Adams, 1971; Bilodeau, 1966; Newell, 1976). The number of original feedback practice trials utilized in the current experiments was generally sufficient to prevent significant immediate decrements in performance on feedback withdrawal. Thus the reversal of performance levels identified by Salmoni et al. (1984) during the KR withdrawal phase is probably due to variations in the number of actual practice trials or trials with augmented feedback, rather than the nature of the augmented information per se.

In summary, the.findings of these experiments imply that application of information feedback techniques to speech production (Nickerson, Kalikow and Stevens, 1976), sport skills (Howell, 1956), and the rehabilitation of self-help skills (Gapis, Grabois, Borrell, Menken and Kelly, 19821, requires a thorough understanding of the task to be learned and the constraints that determine optimization criteria for a given individual. Our experiments show that the issue for augmented information feedback is not merely one of presenting kinematic information as opposed to outcome KR information. In particular the task analysis must include a determination of the degrees of freedom requiring constraint in the task and the control space representation that will unambiguously define the criterion and limb trajectory in space-time. This orientation provides the background to the application of augmented information feedback because recent evidence (Newell et al., 1983, 1985), together with the findings of the current experiments, are consistent with the proposition of Fowler and Turvey (1978) that the augmented information available must match the degrees of freedom requiring constraint in the movement sequence.

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ACKNOWLEDGEMENTS

This work was supported in part by the National Science Foundation Award BNS 83- 17691. We would like to thank Gilmarcio Sanches and Alex Antoniou for help with data collection. Special appreciation is extended to Steve Alexander and Phil Goldberg for software development. Requests for reprints should be addressed to: K. M. Newell, Institute for Child Behavior and Development, University of Illinois, 51 Gerty Drive, Champaign, Illinois 61820, U.S.A.

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