85-411/711 Cognitive Processes and Problem Solving Homework #4 Handed out: 9/19/00 Due: 9/26/00 A. Reading first. Read chapter 4.5 (The functional equivalence of problem solving skills) from MOT vol. I (Simon I). Pay special attention to the section on the "Perceptual Strategy." B. Starting up the simulation. 1. Copy the OPS5.sea file from the Homework #4 folder on the server to your local hard disk (this is the same file as the one used in Homework #3, so if you've already copied it to your hard disk or floppy, there's no reason to do so again). 2. Extract the files from the archive by double-clicking on the OPS5.sea file. Hit 'return' and it will automatically create the files. 3. Start-up OPS5 by double-clicking on the OPS5 program. 4. Now you are in the lisp environment, in which the OPS5 program was developed. - Always hit return after entering a statement in the listener. - Remember to type the parentheses, as well. All commands in LISP are surrounded by parentheses. - If your session goes awry, quit LISP and begin again. If you continue to have problems, don't hesitate to come see me (BH455B) or send e-mail to (kenkwok@cmu.edu). 5. Load the perceptual strategy rules. Choose the "Load" option in the "Eval" menu. In the dialog window, scroll the window until you can see the "perceptual.ops" file. Double-click on "perceptual.ops." C. Running the simulation. The file "perceptual.ops" contains OPS-5 code to implement the perceptual strategy for Tower of Hanoi. In addition to using a different strategy, this code uses a different representation of the problem than the code for the move-pattern strategy (from Homework #3). In the move-pattern code, the pegs included a field which lists disks. In this code, each disk contains a field saying which peg it is on. This representation simplifies the OPS code a little, since we don't need litval to work with lists of disks. 1. Enter (watch 1) This statement sets the debugging level. Now, whenever a production fires, OPS will print the production. To turn off this debugging, type (watch 0). (watch 2) will trace WMEs entered and removed from memory. 2. Enter (run 19). This will allow 19 rules to fire. 3. When asked how many disks, enter 4. 4. When asked which start peg, enter A. 5. When asked which target peg, enter C. 6. Examine the contents of working memory using (ppwm). 7. Examine the conflict set by entering (conflict-set). 8. Suppose the subject were interrupted at this point and lost track of her goal stack. Remove the two goals [using (remove x) where x is the number of the wme representing the goal] to simulate this situation. 9. Examine the conflict set again by entering (conflict-set). What changed in the conflict set and why? 10. Start the simulation running again. What happens? Is the subject able to recover after interruption? 11. Enter (remove-all) and (make start) to start new simulations. 12. Run the simulation using 3, 4, and 5 disks. (using disks A and C as start and target pegs.) Examine the elements of working memory every few rule firings (by using (run 3) and (ppwm) repeatedly). How is the size of working memory affected by the number of disks in the problem? Which elements of OPS5 working memory represent psychological working memory? 13. Modify STARTUP so that the problem starts with disk 3 on peg A, disk 2 on peg B and disk 1 on peg C. Do this by entering the following rule: (p startup (start) --> (make peg ^name A) (make peg ^name B) (make peg ^name C) (make disk ^size 3 ^on-peg A) (make disk ^size 2 ^on-peg B) (make disk ^size 1 ^on-peg C) (make place-disk ^number 0) ; don't place any disks (make target-peg ^end-peg C)) Can the system solve the task? Note, this new rule replaces the old start-up as well as making useless the "place-disks" rule. Try another initial state of your own design. Can it solve the task? After you enter the rule, you will need to do a (remove all) and then (make start). 14. Compare the move-pattern and perceptual strategies in terms of their use of working memory, resistance to interruption, and abilities to generalize to problems of different numbers of disks and different initial and goal states.