OBTENCION DE HARINA DE OCARA DE SOYA

The purpose of this study was to examine the effects of externally focused (task related) versus internally focused (movement related) instructions on simulated upper extremity amputees’ movement kinematics when learning a novel functional movement task. This chapter contains a discussion and interpretation of the results of this

experiment. The results will be discussed in the context of the present hypotheses and other research in this area. Comments made by participants during debriefing will be included and suggestions for further research will be offered.

Overall Findings

The present results indicate that instructions designed to manipulate attentional focus while learning a novel task in a simulated rehabilitation setting can significantly affect motor learning and performance outcomes. The sole variable that was consistently influenced by attentional focus instructions during both the skill acquisition and retention sessions was the amount of cereal spilled. Findings indicated that the external focus group produced significantly less cereal spillage than the internal focus and control groups. Importantly, this increased accuracy was achieved with movement times that were similar to, or faster than, the other groups. Concerning the retention trial results, findings suggest that attentional focus instructions did not significantly impact motor

performance for the following variables: movement time, movement units, plate pitch, and plate roll. Finally, subjective comments by participants in the control group revealed that most preferred to use an external attentional focus approach while learning to perform the task.

The first hypothesis predicted that during the retention session of the study, movement time would be faster for the external focus group than for the internal focus and control groups for each of the subtasks and for overall movement time. The results suggest that, while the externally focused and no instruction conditions consistently produced faster movement times than the internally focused instructions, there were no significant differences between the three conditions. Therefore, the first hypothesis was not supported. The results also showed that movement times improved across all three conditions during the acquisition sessions, suggesting that external focus instructions, internal focus instructions, as well as no explicit attentional focus instructions led to improved performance on this task during the acquisition phase. The finding that the external focus group did not perform significantly faster than the other groups in

retention does not coincide with most of the literature, where the majority of the findings show significant group differences favoring external focus in retention (Singer et al., 1994; Wulf et al., 1998; Wulf et al., 2001). One possible explanation for this finding is the generally low statistical power of this study. It may be that significant differences between groups could be detected with a larger sample size.

The second hypothesis predicted that during the retention session, movement organization for the task, as defined kinematically by the total number of movement units, would be most efficient for the external focus group. This hypothesis was also not

supported by the results of this experiment. Contrary to expectations, the control group consistently produced the fewest movement units. Although not statistically significant, this difference was most salient during the first session, where the mean number of movement units was 47.3 for the control group, 59.4 for the external group, and 66.9 for the internal group. As the experiment progressed to the retention session, the number of movement units decreased for all groups, but more markedly for the internal and external focus groups, nearly creating a point of convergence for all groups at 44 movement units. There is support for this finding in the literature. In Fasoli et al.’s (2002) functional reach study with stroke patients, the only significant results for movement units were found in the control group for two of three tasks. In that study, the authors suggested that

percentage of time to peak velocity and movement units may not be a sensitive outcome variable for detecting the effects of instruction on reach with persons with stroke. This suggestion may apply as well to detecting the effects of instruction on simulated amputees learning to perform an activity of daily living.

A possible explanation for why the control group initially produced fewer movement units rests with Fitts’ Law (Fitts, 1954). Fitts’ Law states that an inverse relationship exists between the difficulty of a movement and the speed with which it can be performed, also known as the speed-accuracy trade-off. In this experiment, although the instructions for the control group requested that participants perform the task as quickly and accurately as possible, the results suggest that the control group’s bias was toward speed rather than accuracy. During the first session, the control group had the fastest TMT of 14292 ms, while it dropped 119 more cereal pieces (or 1.5 times more) than the external focus group. If mere completion of the task was valued more than

accurate completion of the task, then it is feasible that less care would be taken during task performance. This emphasis on speedy completion during sessions 1 and 2, in turn, would produce a smoother, more homogenous movement, since the care and attendant movement unit velocity changes required to accurately position the prosthetic hook for picking up and pouring the cereal would be minimized. When, during retention, all groups were allowed to perform as they wished, these differences, while still not statistically significant, were less pronounced.

The third hypothesis predicted that, during retention, movement stability, as defined kinematically by the amount of plate pitch and roll during transfer of the cereal, would be greatest for the external focus group. Results showed that all groups performed similarly, falling within one-third of a degree (Figures 16 and 17). Therefore, this

hypothesis was not supported by the results of this experiment. Notably, during session 1, the control group displayed more pitch and roll than the external and internal focus groups. This result may also be a reflection of the speed-accuracy trade-off (Fitts, 1954).

A potentially important observation that was not captured by statistical analyses concerning this segment of the task should be noted. As the plate was picked up and moved over the 3.5 cm barrier to the target area, the external focus and control groups were observed to perform the task while sitting upright, flexing and horizontally adducting the shoulder, and flexing and extending the elbow as necessary. Conversely, the internal focus group often kept the shoulder and elbow joints rigid in an attempt to perform the motion by twisting the trunk or by rotating on the chair. The movement tended to appear as a one piece motion that did not have segmental independence. This segmental joint rigidity proved to be expedient in completing the task, but appeared to be

a less efficient movement strategy. The “constrained action hypothesis” (Wulf, McNevin, & Shea, 2001), suggests that when individuals adopt an internal focus, they try to

consciously control their movements. This conscious control inadvertently disrupts the automatic control processes and hinders effective movement, which may account for the observations made during this segment of the task.

The fourth hypothesis for this experiment was that, during retention, the amount of cereal spillage would be least for the external focus group. This hypothesis was supported by the results of this experiment. Importantly, this increased accuracy was produced with an external focus group TMT that was slightly faster than the other groups. The results suggest that external focus instructions produced a movement pattern that was as fast and smooth as the other groups, but with significantly less spilled cereal. Therefore, there is no evidence that a speed-accuracy trade-off was operating. This is an important finding, since, on a therapeutic level, less cereal spillage might produce more self-esteem and satisfaction during the process of learning how to use a prosthesis. In Lake’s (1997) simulated upper extremity prosthesis study, he found that the individuals who received prosthetic training performed activities of daily living in a skillful, efficient manner, exceeding the performances of the untrained control group in all tasks. However, significant differences were found in only two tasks. When the results of Lake’s study are considered with the present findings, it appears that modifying prosthetic training

protocols so that the use of external attentional focus is emphasized may produce optimal motor learning results.

Concerning the amount of cereal spilled during sessions 1 and 2, the external group spilled more cereal during the second acquisition session than the first, while the

internal focus group had the opposite effect. Furthermore, the control group spilled relatively similar amounts during both sessions. These results must be considered in light of decreasing TMTs for each group. In reviewing the literature, studies by Perkins-

Ceccato (2003) and Black (2004) both found that, over time, novice participants receiving internal focus instructions tended to improve their performance, and that external focus participants, who at first tended to outperform their cohorts, gradually lagged in performance. The present results tend to agree with those findings. On the other hand, the control group spilled similar amounts of cereal during sessions 1 and 2 while also decreasing TMT. In terms of cereal spilled, by the second session, the control group performed the worst (Figure 14). It was observed during the experiment that, relative to the other groups, the control group seemed more concerned with finishing the task than with cereal spillage. Since this question was not specifically explored during the post-experiment interview, this observation remains speculative. Nevertheless, this interest in simply completing the task may explain the lack of improvement by the control group.

The significant session x trial interaction for MT2 during session 1 was likely the result of a single trial, during which the performance on session 1 dramatically improved and the performance on session 2 decreased. Because this was a single trial, and not a general trend, it is difficult to attach much practical importance to this finding. Because the TMT and TMU results were impacted by a trial that followed a verbal attentional focus reminder (trial 4), there may be a relationship between impaired performance and the verbal cue. However, because there were also just as many, if not more, trials that did not follow verbal cues that also impacted the results, this explanation can only be partial

in scope. The MT1 group x session interaction showed that, while the internal focus and control groups displayed similar rates of MT1 improvement between session 1 and 2, the external focus group gained considerably more speed between sessions relative to the other groups. The external focus group improved 302 ms between sessions, while the internal focus group improved 16 ms, and the control group improved 47 ms. Since MT1 encompasses the start of the activity to picking up the cup of cereal, this result suggests that using external focus instructions to teach a complex movement pattern may improve the quality of the initial movement phase. Alternatively, this may also show that the instructions were fresh in the minds of the participants, and that they adhered to the instructions more diligently during the early phase of the task. Finally, results showed that the external focus group was significantly faster than the internal focus group, but not the control group, for MT3 during sessions 1 and 2. This phase of the task, which involved picking up the bowl of cereal with the prosthesis and placing it on a plate, required precise motor control to pick up the bowl. It was observed that the internal focus group had more difficulty picking up the bowl than the other groups. Therefore, as Wulf and Prinz (2001) suggest, it appears that external focus instructions enhanced the skill acquisition process for this part of the task.

The participants’ debriefing comments during retention are relevant to the interpretation of the results of this experiment. Since the control group did not receive any attentional focus instructions, it was of interest to determine what their natural attentional bias had been. Nine of the ten participants in this group elected to adopt an external focus strategy by paying attention to the cup, bowl, plate, or cereal in the cup. Only one participant chose an internal focus strategy by attending to his posture and

trunk, and shoulder at times, as he performed the task. The inclination to adopt an external focus of attention agrees with the findings of Wulf, Shea, & Park (2001). In Experiment 2 of that study, participants were given two practice sessions to learn how to perform a balancing task on a stabilometer. During these sessions the researchers

provided internal and external focus instructions, and participants were free to switch between the approaches during practice if they desired. The authors found that on day three, which was a retention session, most participants chose an external focus strategy.

Regarding the debriefing responses of the external and internal focus groups, the majority (75 %) stated that they continued to use the same attentional focus strategy they had used during both acquisition sessions. However, five participants out of 20 reported switching their attentional focus for the retention session. Of the five who switched, two were external focus and three were internal focus participants. While the two external focus participants reported adopting an internal focus strategy for only a specific part of the task (pronation and supination while pouring the cereal), the internal focus

participants reported using an external focus approach for most, if not all, of the task. There is support in the literature for these apparently contradictory results. In the case of the two external focus participants who switched to an internal focus preference while pouring the cereal, the findings of Perkins-Ceccato et al. (2003) may provide an

explanation. In that golf study, the authors found internal focus to be more beneficial than external focus to novices who were learning how to perform a golf pitch shot. Although the Perkins-Ceccato study did not investigate attentional focus preferences, per se, it may be that participants in the present study adopted an internal focus because they did not yet feel skilled enough to perform the pouring motion without attending to their wrist. In the

case of the three internal focus participants who adopted an external focus, the findings of Wulf, Shea, and Park (2001), as discussed previously, may provide an explanation. In Experiment 2, novice participants, when given a choice, were shown to prefer external attentional focus. In the current study, when participants were not explicitly directed to use internal attentional focus, three of ten reported choosing external attentional focus. A difference with the current findings is that participants were never provided external focus instructions, and so had to essentially come to this approach on their own.

Based on learning the motor task used in this study, there may be some implications for occupational and physical therapists working with upper extremity amputees. First, instructions that emphasize an external attentional focus strategy may be used to improve movement accuracy when recalling how to perform the task.

Importantly, this accuracy is not gained at the expense of movement speed. Second, during practice sessions, external focus instructions may improve both movement speed and accuracy. Notably, this improved movement accuracy and efficiency may foster higher acceptance rates of upper extremity prostheses. Third, the results show that internal focus instructions clearly did not result in improved movement efficiency or accuracy. Thus, when presented with the opportunity to use internal or external focus instructions, a bias toward external focus instructions should be adopted. Finally, performance results of the control group suggest that when attentional focus instructions are omitted, movement accuracy is sacrificed for movement speed, thus causing

undesirable cereal spillage. Therefore, not providing instructions may lead to unwanted errors, and create frustration which, ultimately, may result in rejection of the prosthesis. This finding suggests that prosthetic training by a skilled therapist will be more beneficial

than reducing or omitting therapy and allowing the patient to self-train on how to use the prosthesis.

Conclusions

Based on the findings of this study, the following conclusions are made: 1. Movement time and movement units are not affected by instructions

designed to manipulate attentional focus while learning how to perform a novel task with a simulated prosthesis.

2. The amount of pitch and roll that may occur while learning to pick up and move a plate with a simulated prosthesis is not affected by instructions designed to manipulate attentional focus.

3. The amount of cereal spillage that may occur while learning to pick up a cup of cereal, pour the cereal into a bowl, and pick up and move the bowl with a simulated prosthesis is significantly affected by instructions that promote an external attentional focus.

Recommendations for Further Research

The findings of this study form the basis for the following recommendations for further research:

1. Further attentional focus research should be performed with participants who have an actual clinical condition, rather than a simulated condition. Participants who have the condition being investigated may have a higher level of investment in the experimental outcome than individuals

simulating a condition. From a performance standpoint, in the present study, genuine amputees would have demonstrated different movement kinematics, since the length and weight of the affected limb would be less. In turn, this may have had a bearing on the experimental outcome, since they would move differently in a prosthesis. From a cognitive standpoint, since some conditions impact mental performance, attentional focus instructions may have different impacts upon motor learning in patient populations with cognitive impairments. Stroke and multiple sclerosis are two examples of conditions that are suitable for investigation.

2. Future studies should incorporate more complex activities of daily living. The increased difficulty may heighten mental and physical demands, thereby allowing subtle differences in motor performance to become more discernable.

3. The current study took place at a table with the participant seated on a seat that rotated. The seat permitted trunk rotation during subtask four where the upper extremity crossed midline. Future studies should use a fixed chair to prevent this compensatory movement strategy while crossing midline. This, in turn, may significantly impact dependent variables during subtask four.

4. Future studies should investigate the area of attentional focus preference for novices in a rehabilitation setting.

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