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Cycling In Repeated-Event Laboratory Testing
Sequencing can be quite complex in repeated-event laboratory testing, as in vision research, cognitive research, and human factor research. One complication is that a subject gets the same treatment and measurement combination more than once and often more than one treatment and measurement combination more than once. These are sometimes called "crossover designs." One consequence is that subjects will memorize repeated measurements and that can undermine the validity of the tests.
What is generally required is the same basic measurement, but with "equivalent materials." To illustrate this problem, think of the presentation of a large matrix of letters where the subject's task is to count the occurrences of a particular letter. Obviously, if the same matrix were presented in every cycle with the same test letter, subjects would soon recognize the matrix and the locations of the test letter. Therefore, the matrix of letters must be randomly re-constructed every cycle and the subject must be given a randomly generated test letter. These are "equivalent material measurements" They should not be confused with treatments (stimuli), which, for example, might be something like font type, background color, or illumination.
Another example would be in a reading speed and comprehension study in which a subject is presented a passage of text and then presented a question about the contents of the passage. Obviously, the passage of text would have to be different for every event cycle and the comprehension questions would have to be coupled to specific passages.
Another potential complication is that experimenters may want to cycle groupings of treatments and measurements rather than individual events. To handle this situation, click on the "Cycle Event" button to the right of the Execution List. On the right side of the dialog is the list of events that you copied into the current group. To make a "grouping" of events from this list, click on the first event and then on the left arrow. That event now appears in the window on the left. Repeat this process until you have your grouping defined. Note that "groupings" are simply run-time collections of events are have nothing to do with experimental groups, such as a treatment group or control group.
An example of a "grouping" in a study of the effects of color on reading performance might consist of three events, using tinted lenses, tinted display background, and standard black with white background. This "grouping" can now be cycled two ways. The first is to present each event in order K times. The second is to present the grouping (list) K times. These options are presented in the cycle events dialog.