This is an ACT-R model of the Friedman, Burke, Cole, Keller, Millward, and Estes (1964) button choice experiment. In the experiment subjects were to press one of two buttons on each trial, and were informed after choosing whether it was the correct button. The correct button to press was randomly chosen on each trial, with a probability p for button 1 and 1-p for button 2.
The experiment used a within-subjects design so that each subject experienced multiple probability conditions (i.e., the probability p that button 1 would be correct varied across blocks of 48 trials). All odd-numbered blocks had p = 0.5. Even-numbered blocks had p drawn randomly (without replacement) from the set {.1, .2, .3, .4, .6, .7, .8, or .9}. The running model in this example outputs choice proportions for the even-numbered blocks, with each such block broken into 4 sub-blocks of 12 trials each. This break-down shows how the model transitions from the preceding 0.5 block to the current variable-p block.