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Start the demonstration by pressing the "Run" button. Keep the lower line (the cursor) directly under the upper line (the target) by moving the mouse to compensate for the disturbances to the cursor. The disturbances are time varying waveforms. The word "Repeat" that is printed during a trial marks the point where the disturbance waveform repeats. A graph of the results appears after several seconds of tracking. Press the "Run" button at any time to restart the tracking task.
The responses (mouse movements) that keep a stimulus (like cursor position) under control in a tracking task occur in a closed loop. The stimulus in this loop (the controlled variable) is both a cause and an effect of responses. This means that Stimulus-Response (S-R) explanations of control won't work. An S-R interpretation of control says that something about the stimulus (such as how far the cursor is to the left of right of the target) causes you to respond in just the right way so that the cursor stays close to the target.
In the Nature of Control demonstration it was shown that the correlation between cursor (S) and mouse movements (R) was nearly 0.0. This suggests that cursor movements are not the cause of the mouse movements that keep the cursor on target. However, the S-R correlation could be low because we not are measuring the aspect of S that is the actual cause of R. Rather than attempting to find the aspect of S that causes R, the present demonstration tests whether any aspect of S can be found that causes R. If some aspect of S does cause R then if variations in R on two different occasions are the same, the variations in S on these two occasions should be the same as well.
In this demonstration you produce identical variations in R during two successive periods of a tracking task because the disturbance to the controlled variable (S) is the same during these two periods. A graph of the results of the experiment will be displayed automatically as soon as you have completed both periods of the tracking task (after approximately 30 seconds of tracking). The graph will remain on the screen until you start the tracking task again by pressing the "Run" button.
The left side of the graph shows the results for the human subject (you); the right side of the graph shows the results for a simple control model doing the same task. Note that variations in R during the first (large black squares) and second (large red squares) periods of the experiment are virtually identical for both subject and model. The R1- R2 correlation between response variations during these two periods is typically on the order of .99. Note that the variations in S during the first (small black squares) and second (small red squares) periods of the experiment are not identical for both subject or model. Indeed, the S1-S2 correlation between stimulus variations during these two periods is typically far lower than the correlation between response variations during the same periods. The S1-S2 correlation is on the order of 0.0 to 0.5.
The results of this demo are so surprising that some have suggested that the high correlation between R1 and R2 results from the fact that the subject is simply repeating the mouse movements made during the first part of the experiment from memory. This would presumably explain why there is a high correlation between R1 and R2 when there is a low correlation between S1 and S2. The subjust is matching second phase mouse movements (R2) to those made in the first phase (R2) without even watching the cursor. You can test the plausibility of this explanation by closing you eyes after the word "Repeat" is printed and trying to imitate the mouse movements you made prior to seeing "Repeat" with those you make after it. If the "repeated movements from memory" explanation is correct you should again obtain a high correlation between R1 and R2 while there is a low correlation between S1 and S2. And cursor variations before and after the "Repeat" (S1 and S2) should also stay close to the target, as they dis when you were actively controlling cursor position. You will see that the "repeated movements from memory" explanation fails because the correlation between R1 and R2 will be quite low and, while the correlation between S1 and S2 will also be low, you will be able to see from the graph that the stimulus traces, S2, in the second phase (with movements made form memory) stay nowhere near the target. The results of this experiment shows that there is no aspect of the stimulus input to a control system serves as the cause of the responses that control that input. S-R causality and control are two different phenomena.
The results of this demonstration are best when you are able to control the cursor well. The better your control of the cursor, the lower will be the correlation between stimulus variations during the two periods of the tracking task.