Resultados obtenidos

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 presents the method of the study and includes the following sections: (a) participants and design, (b) task and apparatus, (c) procedures, and (d) data treatment and analysis.

Participants and Design

Thirty university students, 17 females and 13 males, ranging from age 19-26 participated in the study. Participants had no prior experience with the experimental task and were not aware of the study purposes or hypotheses being tested. All participants were screened via questionnaire for right hand dominance. Informed consent was obtained from each participant before beginning the experiment (Appendix A). In order to be included in the study, the following additional criteria were met:

1. No medical history of nervous or musculoskeletal conditions, including arthritis, carpal tunnel syndrome, unhealed shoulder/wrist/hand injuries (breaks/sprains/neurological damage/surgeries), or any diseases of the upper extremities or peripheral circulatory systems.

2. No current use of any medication (stimulant or depressant) that may have caused drowsiness, fatigue, increased heart rate, or increased blood pressure.

3. No current ailments associated with undue daily fatigue.

The experiment had two phases: 1) skill acquisition, which took place during sessions 1 and 2 of the study, and 2) skill retention, which took place during session 3 of the study. The design was a 3 x 2 x 10 (Group x Session x Trial) factorial for sessions 1 and 2, with repeated measures on session and trials. For session 3, which was a retention session, the design was a 3 x 10 (Group x Trial) factorial design with repeated measures on trials. In both cases levels of the first factor were the internal focus, external focus, and control groups. Levels of the session factor included acquisition session 1 and acquisition session 2. Levels of the third factor were the 10 trials per session. The dependent variables included segmental and total movement times, the number of movement units, the amount of pitch and roll during movement segment four, and the amount of cereal spillage that occurred during task completion.

Data collection took place over three separate sessions, during which each participant completed the experimental task ten times, for a total of 30 trials. On the first two skill acquisition sessions, participants received, depending upon the experimental group to which they had been assigned, video instructions concerning how to perform the task. On the retention session, participants did not receive any instructions about what to pay attention to while performing the task.

Task and Apparatus

Task Description

The experimental task was to perform an activity of daily living with a prosthesis that simulated a left arm transradial amputation. Participants used the prosthesis with the nondominant (left) upper extremity to pick up and empty a cup of cereal into a bowl, place the bowl on a plate, and move the bowl of cereal and plate across their midline to a new location (Figure 6).

Starting Position

The participant was seated on a stool adjusted to a height that allowed for efficient completion of the task. The participant’s left shoulder was adducted to the side with the elbow flexed at 90°; the left forearm was in the power grip neutral position, with the hand grasping a wooden dowel within the distal end of the simulated prosthesis.

Electromagnetic tracking sensors were placed on the skin of the lateral aspect of the participant’s humerus, and also midway down the lateral aspect of the prosthetic simulator. A piece of foam on the underside of the prosthesis rested on top of a push switch. The participant’s right forearm and hand rested on the right leg underneath the activity table. Once the participant was asked to start, the left shoulder flexed and the elbow extended, thus lifting up and moving the tip of the prosthesis 12 cm toward an aluminum cup filled with 1 cup (250 pieces) of Cheerios® cereal. The aluminum cup completed an electrical circuit which was broken when the cup was lifted off the table. The prosthesis grasped the right side of the cup of cereal, which was then moved via left shoulder horizontal adduction or trunk rotation toward an aluminum bowl, the center of which rested 20 cm to the right of the cup’s center. The cup of cereal was then poured in the bowl via left forearm supination. Once the bowl had been successfully filled with cereal, the empty cup was returned to its original position. The participant then picked up the left side of the bowl of cereal with the prosthesis and used left shoulder extension and elbow flexion to carry the bowl back (toward the trunk) and placed it on a plastic plate, the center of which was 30 cm from the bowl. The plate, which was elevated 4 cm, had a sensor on the bottom that transmitted kinematic data to a Motion Monitor version 6 (manufactured by Innovative Sports Training). Specifically, the sensor provided pitch

(movement about the Y axis) and roll (movement about the X axis) data during movement (Figure 7). The plate was then picked up, and moved over a 3.5 cm high barrier and across midline to a target area the center of which was 40 cm to the right of the plate. The sensor beneath the plate indicated initiation and cessation of plate motion. Analog signals from the voltage switches and electromagnetic sensors were sampled simultaneously, allowing for synchronization of kinematic and movement time data.

Test Apparatus: Work Station

The test apparatus work station consisted of a wooden particle board table (2 cm thick) situated 66 cm off the floor. A 142 cm wide x 81 cm deep space on the work station surface was covered with black poster board with spaces cut out for the contact switches and designated target areas (Figure 7). The far side of the table rested against a blank white wall. Participants sat on an adjustable stool 35-48 cm high. The stool had no back, which allowed for trunk flexion and extension during completion of the task. The seat of the stool was not fixed, and was free to rotate 360 degrees.

The aluminum cup was 9.5 cm in diameter and 5 cm deep and held 250

Cheerios®. The aluminum bowl was 14.5 cm in diameter and 4.5 cm deep. The plastic plate was 25 cm in diameter and had a lip that was 2 cm deep (Figure 6).

Test Apparatus: Simulated Prosthetic Device

The prosthetic simulator (Figure 8) was designed to mimic a prosthetic device for an upper extremity transradial amputation that allows for forearm supination and

pronation. Additionally, the simulator was fabricated almost completely from non-ferrous materials (primarily aluminum and fiberglass) so that the Motion Monitor was able to

track and record experimental movements without signal anomalies or artifacts. The simulator had a figure-8 harness that was attached to a steel cable that ran across the

Cup Switch Bowl Switch

Plate Start

Plate Stop Start Switch

x

y

Figure 7. Contact switches and axes orientation.

back and upper arm on which the prosthesis was worn. The control cable was the only part of the simulator that contained ferrous materials. Through pilot testing, it was determined that the cable did not limit the Motion Monitor’s ability to gather accurate kinematic data. The steel control cable inserted onto an aluminum split hook (5XA) terminal device, which has been used with regular prostheses. The prosthesis was fitted with a left handed terminal device. The device was a voluntary opening device; that is,

three one-pound tension rubber bands held the terminal device in the closed position, and it was opened by adjusting the tension of the cable with synchronized motions of the

Figure 8. The prosthetic simulator.

opposite shoulder, torso, and involved upper extremity. In order to wear the simulator, participants placed their left arm in a fiberglass sleeve and moved their hand to the distal end of the simulator where a wooden dowel was grasped (power grip) with the left shoulder adducted to the side, the elbow flexed to 90 degrees, and the forearm in the power grip neutral position. Velcro straps were then adjusted and secured. The figure-8 harness was then tightened by an assistant. Proper fit was determined by asking the participant to flex the shoulder and extend the elbow in order to open and close the

terminal device. If the participant was able to open and close the prosthesis without difficulty or discomfort, then it was determined that proper fit had been achieved.

Kinematic Measurement Apparatus

Data collection occurred in the Auburn University Musculoskeletal Research Laboratory (1403 Haley Center). Three-dimensional kinematic variables were assessed using the Motion Monitor version 6 (Figure 9) electromagnetic tracking system

(Innovative Sports Training, Inc., Chicago, IL, USA). The electromagnetic sensors had root-mean-square position accuracy of 1.78 mm/0.5° and a resolution of 0.76 mm/0.1° within a 0.91 m operating range. Timing of the separate movement segments was measured by three electrical contact switches and one sensor that were tracked by the Motion Monitor system. Three electrical contact switches (Figure 7) were connected to the Motion Monitor to provide data about movement times for the first three segments of the task. The start position switch was a push switch that was activated by pressing down on it; that is, the circuit was completed when it was pushed down by a piece of foam attached to the underside of the prosthetic simulator. The second and third switches consisted of two sets of aluminum plates (5.5 cm x 12.1 cm) soldered to wires powered by a GW Labs GPS 1850 DC power supply, which provided 5 volts of continuous current. These switches were closed until the circuit was broken by removing the aluminum cup on the first set of plates, and the aluminum bowl on the second set. All circuits were split so that the signal traveled to both the Motion Monitor and to a four channel 100 MHz digital oscilloscope (Tektronix model number TDS 2014) that was continuously checked to ensure that all switches and circuits were functioning properly.

Figure 9. The Motion Monitor version 6 electromagnetic tracking system.

Procedures

All participants signed an Informed Consent form (Appendix A) before testing began. They were then asked to remove all jewelry from their left upper extremity and to turn off any mobile phones or pagers, which might cause a distraction during testing. Participants were serially assigned to one of three groups: internal focus, external focus, or control, based on the order in which they were scheduled to attend the

experiment. A restriction that each group contain a similar number of males and females was enforced, so that the external focus group had 5 males and 5 females, and the internal focus and control group each had 6 females and 4 males. After arriving at the lab, the participants were fitted with the simulated prosthesis and, prior to the first session,

watched a one-minute video tape that demonstrated how to use and control the prosthetic simulator. The script of the first video instructions appears in Appendix B. Participants did not watch this video before the second or third sessions. Before acquisition sessions one and two, each group watched a second video, of which there were three versions. This video contained instructions designed to induce internal, external, or no specific attentional focus, and a demonstration about how to perform the experimental task. On session three, which was a skill retention session, no video instructions were provided. The scripts for each condition were:

External-focus condition: “While completing the following task, pay attention to the cup, bowl, and plate during each part of the task. The task is as follows: lift the prosthesis off the table and grab the right side of the cup of cereal. Next, pour the cup of cereal into the bowl and then return the cup to its original place. After this, pick up the bowl and place it on the plate. Then, move the plate and bowl to the location marked with a red square. Move as quickly and

accurately as possible. Remember to pay attention to the cup, bowl, and plate, and think about them during each part of the task. Later, I’m going to ask you a question about this. Begin after I say ‘go’.”

Internal-focus condition: “While completing the following task, pay attention to your shoulder, elbow, and wrist as you move the prosthesis during each part of the task. The task is as follows: lift the prosthesis off the table and grab the right side of the cup of cereal. Next, pour the cup of cereal into the bowl and then return the cup to its original place. After this, pick up the bowl and place it on the plate. Then, move the plate and bowl to the location marked with a red

square. Move as quickly and accurately as possible. Remember to pay attention to your arm. Think about how much your shoulder, elbow, and wrist move during each part of the task. Later, I’m going to ask you a question about this. Begin after I say ‘go’.”

Control Condition: “The task is as follows: lift the prosthesis off the table and grab the right side of the cup of cereal. Next, pour the cup of cereal into the bowl and then return the cup to its original place. After this, pick up the bowl and place it on the plate. Then, move the plate and bowl to the location marked with a red square. Move as quickly and accurately as possible. Begin after I say ‘go’.” After playing the instructions on acquisition sessions one and two, or immediately on retention, the participants were taken to the test station and asked about how much sleep they had the night before. The answer to this question was noted. Once at the testing station, a mechanical model of the forearm segment/prosthesis interface was created by digitization of the elbow joint center and the distal end of the prosthesis. To do this, sensors were fastened to the distal lateral aspect of the participant’s left humerus and to the distal lateral aspect of the prosthetic simulator with double-sided tape and Velcro. Finally, a sensor was fastened beneath the plate with double-sided tape and Velcro. Because there was a 3.5 cm spacer beneath the plate, the sensor did not contact the testing station table.

Once the participant was fitted with the device and sensors, one practice trial was performed to ensure that the task was properly understood. He or she was then told to start the first of ten trials when the investigator said “go.” Data was collected for all ten trials, but not the practice trial. If the participant was in an internal attentional focus

group, reminders to pay attention to the shoulder, elbow, and wrist were given after the third and sixth trials. The script to this reminder was: “Remember to pay attention to your arm. Think about how much your shoulder, elbow, and wrist move during each part of the task.” If the participant was in the external attentional focus group, reminders to pay attention to the cup, bowl, and plate were given after the third and sixth trials. The script to this reminder was: “Remember to pay attention to the cup, bowl, and plate during each part of the task.”

After completion of the tenth trial, participants in the internal and external focus groups were asked the following question: “What did you pay attention to as you completed the task?” After answering this question, the participant was free to leave for that session.

The study took place over three sessions – one session per day for three days with at least one day in between, ideally Monday-Wednesday-Friday, and during the same time on each day. The time between sessions did not exceed 72 hours. During each session, participants performed the task ten times.

Data Treatment and Analysis

Onset algorithms for the analog circuits and plate movement were employed using custom software (LabVIEW 7, National Instruments, Austin, TX). Respective onsets were defined as the time instances when each analog signal exceeded the mean and a specified standard deviation multiple for a specified time interval. These mean and standard deviations were calculated for each signal over the initial 100 ms interval.

A digital analysis package was used to filter kinematic data at a frequency of 10 Hz, using a second-order low pass Butterworth filter. The filtered data was then

processed with a custom-written program to yield the following kinematic variables: movement times, movement units, pitch, and roll. Movement times were measured in milliseconds; pitch and roll were measured in standard deviations of degrees. Movement units were defined via two mechanisms. The first defined the onset of a movement as the point when the velocity exceeded 50 mm/s for at least 200 ms. Then, within that

movement onset, accelerations were defined as changes of 5 mm/s2 for at least 20 ms. This definition of movement unit is consistent with that provided by Fasoli et al. (2002). Using these parameters for determining a movement unit, custom written software calculated the number of movement units for each trial analyzed.

Data was collected during three experimental sessions. Acquisition data were analyzed with a 3 (Group) x 2 (Session) x 10 (Trial) ANOVA with repeated measures on the second and third factors. The Retention session analysis was a 3 x 10 (Group x Trial) ANOVA with repeated measures on the second factor. For both analyses, the individual dependent variables included segmental and total movement times, the total number of movement units during each segment of the task, the amount of pitch and roll of the plate during the final movement segment, and the amount of cereal spilled during task

completion. The alpha level for the ANOVAs was set at .05. Significant group main effects were followed up with the Sidak procedure at a .05 level of significance. Significant interactions were graphed and described verbally, as recommended by Thomas, Nelson, and Silverman (2005).

To test for significant differences among the three groups on the amount of cereal spilled, a Chi Square analysis was performed. The Chi Square analysis was employed because of unequal variances and because of the small sample sizes. For all analyses, a p- value less than .05 was considered significant.