When you press the "Run" button you will see a salmon colored target disk -- the target disk -- surrounded by six grey disks -- the context. Your task is to control the size of the target disk; that is, keep the size of the target disk as constant as possible: try to keep it about 1/4 inch in diameter. You do this my moving the mouse so as to counteract disturbances to the size of the target disk that are being produced by the computer. This will take a little practice but keep at it until you are able to keep the target disk nearly the same size -- 1/4 inch in diameter -- during a test trial, which lasts about 45 seconds.
At the end of each trial a record of your performance is printed out in the form of graphs and root mean square (RMS) measures of how well you controlled the size of the target disk. RMS measures performance in terms of the deviation of the size of the target disk from its average size during a trial; the smaller the RMS value, the better your control of the size of the disk. Once you have gotten the RMS number in the upper left corner of the print out of the results (the one labeled "RMS Area 1") to be as small as you can get it you can come back and read the rest of this write up to find out what the demonstration shows.
You will have noticed that there were two phases of this demonstration. During the first phase (1) the size of the six context disks was constant; during the second phase (2) the size of these context disks varied from small to large. When you look at the results of the demonstration you should see that your control of the size of the target disk was much better during phase 1 than it was during phase 2 of the demonstration. An example of the results you might have gotten is shown in the figure below :
The values in the upper left corner of the display, labelled “Area RMS 1” and “Area RMS 2”, are measures of your performance in terms of the accuracy of control of the size of the target disk during phases 1 and 2 of the demonstration, respectively. Since the smaller the value of the RMS measure the more accurate the control of the disk, control of the disk was nearly 5 times more accurate in phase 1 than in phase 2 of the demonstration. The reason is clear from looking at the red lines in the graphs.
The red line shows the size of the target disk varying over time. The top graph, labeled “Constant Context”, shows the variation in the size of the target disk during phase 1; the bottom graph, labeled “Variable Context”, shows the variation in the size of the target disk during phase 2. The less the red line varies over time, the better the control of the size of the target disk. Clearly, the red line varies far less during phase 1 then during phase 2. The reason for this is clear from looking at the black line in each graph, which shows the variation in the size of the context disks during each phase. During phase 1 the black line is flat, indicating that the size of the context disks was constant throughout this phase; the only cause of the variation the size of the salmon disk during phase 1 was the computer’s disturbance (indicated by the green line in the graph) and the participant’s mouse movements that were made to compensate for this disturbance. During phase 2, however, the black line varies, indicating that the size of the context disks was varying throughout this phase and the size of the target disk varied in concert with these variations; the target disk got larger when the context disks got larger and smaller when the context disks got smaller. This relationship between the size of the context and target disks would be expected to occur if the participant is controlling a relationship between the size of target disk and the size of the context disks rather than the size of the target disk itself, as instructed.
An instructor unfamiliar with the idea that people control their own perceptions would conclude that the instructee’s performance fell off precipitously during phase 2 of this experiment. This conclusion is based on the assumption that the instructee is trying to control the size of the target disk, as instructed. But even though a person is instructed to control something doesn’t mean that that is what the person is actually controlling. In this experiment, the size of the target disk cannot be perceived independent of the context in which it occurs. When the context is constant it appears that the size of the target disk is being controlled; but when the context varies it becomes clear that it’s the relationship between target and context disks that is actually being controlled.
The “moral” of this demonstration is that instructors cannot assume that instructee’s are trying to control what they have been instructed to control. Instructors must not take it for granted that what they have asked the instructee to control is what the instructee is actually trying to control. Instructors must learn to use a version of the “Test for the Controlled Variable” to determine what the instructee is actually trying to do (what perception the instructee is trying to control).