Introduction

In your lecture we describe the closed-loop mode of control for executing relatively long-duration continuous movements. Using closed-loop control processes, performers can make adjustments during the execution of a task to maintain accuracy. A good example of closed-loop control is tracing a figure on paper. As you follow the lines of the figure, you continually monitor your progress so that your tracing does not deviate from the template provided by the original figure. When it does, you make adjustments to stay on track. To facilitate the use of this type of control, you move very slowly so that you can detect and correct deviations before they are so large that your tracing will be noticeably different from the original figure.

Closed-loop control is used in a variety of situations. A common example is keeping your car in the lane as you are driving along a road. As you drift one way or another, you visually detect that you are headed toward one edge of the lane and make gradual adjustments to your steering to keep the car relatively close to the center of the lane. Not all aspects of driving are controlled using a closed-loop mode, however. For example, rapidly swerving to avoid a suddenly appearing obstacle (such as an animal or object entering your path) occurs far too quickly for you to use the feedback-based adjustments that characterize closed-loop control.

Just because a portion of a movement is executed under closed-loop control, it does not mean that the entire movement is. Think about threading a needle. To get the thread through the hole, you will likely use closed-loop control. But once the thread is through, you can feed an additional length of thread through very quickly without needing to make any adjustments.

Equipment

Stopwatch and this lab printed (student responsibility)

Instructions

Students will take turns in the roles of experimenter and participant. On the following page you will find 24 diagrams containing a shaded path around the central number. Each diagram is used for a single trial. For each trial, the participant’s goal is to draw a line exactly in the center of the gray shaded path, following its shape all the way around the diagram. The movement should be slow and continuous. Begin each trial at the bottom of the star. For the first 12 trials, the participant will use the dominant hand. For the remaining 12 trials, the participant will switch to the nondominant hand. The experimenter will record the time for each trial and record the values on a separate piece of paper along with any other observations about the performance (e.g., the way the pencil is held, changes in speed during a trial). The participant should not be told the times and should not be given any type of feedback. The participant should focus on accuracy (don’t worry about how long a trial takes as long as you are accurate). Collect all data for one participant before switching roles. After data have been collected for both students, you can share your observations about performance with each other.

Data Sheet: Trials

Participant: _________________________________________

Experimenter: _______________________________________

Dominant Hand

5 to 10 seconds between trials

1-minute break

Nondominant Hand

5 to 10 seconds between trials

Data Sheet: Results

Participant: _________________________________________

Experimenter: _______________________________________

Record observations to the right of data tables.

Dominant Hand Data Table

5 to 10 seconds between trials

1-minute break

Nondominant Hand Data Table

5 to 10 seconds between trials

Discussion

Describe your results by noting any changes you might have observed in your performance across the 12 trials (e.g., improvement) for each hand and by comparing your performance between your two hands. Note also whether the amount of time for a trial changed with practice or whether it differed between hands. Discuss how your results illustrated closed-loop control as described in your resources. Describe any aspects of the task that you think might not have been controlled in a closed-loop mode. Discuss two factors other than those controlled in this lab that might have influenced your results.