85-411/711 Cognitive Processes and Problem Solving Homework #5 Handed out: 9/26/00 Due: 10/3/00 Memory for Lists Simulation. Load up the EPAM program from the Mac server. Copy the EPAM program to your local hard disk before running the program. If you kept around EPAM from the last homework, you do not need any thing else. Notes on the MCL environment: - Quit by choosing "Quit" from the "File" menu. - Stop a simulation by choosing "Abort" from the "Eval" menu (or command-.). - If you get an "Error" message, abort the simulation and start that simulation over. - Print the contents of a window to a printer by choosing "Print" from the "File" menu. A. Forward memory strategy. This is a simulation of a how a standard subject approaches the task of remembering a list of arbitrary words. The subject's task is to keep the items in short-term memory until the experimenter gives a signal to report the words back. This simulation assumes that the subject divides short-term memory into three sections. In this simulation, these sections are labeled b-group, m-group, and e-group (for beginning, middle, and end). Generally, words in the beginning of the to-be-remembered list are placed in the b-group, words from the middle are placed in the m-group, and so on. When the simulation does internal rehearsals of the items in short-term memory, it does it one section at a time. 1. Turn all printing off. This is done by selecting each of the items in the "Printing" menu (or use the "all off" option). Selecting one of these items a second time will turn that kind of printing back on. 2. Run the visual-forward experiment 20 times with a list of 10 words. This is done by choosing the "Visual Forward" option in the "Simulations" menu. Enter 20 for the number of repetitions, and 10 for the number of words (this is the default setting). 3. For the simulation, all the words used in the simulation will be entered into the discrimination net. The assumption is that EPAM is already familiar with the words (i.e., can recognize them as familiar chunks), and simply has the task of remembering a subset of the known words in short-term memory. As the words are being entered into the net, the message "Creating network of words" will appear. 4. For each experiment in the simulation, EPAM is presented with 10 words to remember. The words are presented one at a time visually, at a rate of one per 1000 msec. The words appear for only 500 msec, and then disappear. EPAM's strategy is to rehearse the words it sees in the auditory loop until the signal is given for it to repeat back all the words in the list starting from the front of the list. 5. Once the individual experiment simulations begin, the following bits of information will be displayed (assuming that all other printing has been turned off): a) the experiment number; b) the stimulus list of words that are to be remembered (these are chosen randomly); and c) words that EPAM remembered, broken down by section. 6. From these data, draw the serial position curve. First, tabulate how many words in each position were remembered. For example, how many times was the first word in each of the lists remembered? Second, plot how often words were remembered (out of 20 experiments) as a function of serial position in the list. 7. How does this serial position curve compare to the one found with human subjects (as described in the Memory for Lists experiment from assignment 1)? B. Forward memory strategy in closer detail. This time, examine the contents of the auditory loop as EPAM is rehearsing the items. For the forward memory strategy, EPAM rehearses the items by group, in the order: b-group, m-group, e-group. 1. Turn printing of the contents of the auditory loop on by selecting "Imagery Stores" from the "Printing" menu. 2. Choose "Visual Forward" from the "Simulations" menu. This time enter just 1 for the number of repetitions, rather than 20. Enter 10 again for the number of words. 3. Again, the network of words will be put into the discrimination net as the message "Creating network of words" is displayed. 4. After the to-be-remembered words are displayed, the contents of the auditory loop are displayed each time that EPAM rehearses. 5. The auditory loop is a list of short-term memory items. Each STM item is composed of three things: a) a time stamp; b) the auditory name of the chunk; and c) to which group the item belongs. 6. The time stamp indicates how many msec are left before that item will decay from short-term memory. Items must be rehearsed at least every 2000msec or they will decay from memory. As each item is rehearsed it is given a time stamp, which indicates how much time is left before the item decays from memory. The time stamp is initialized to 2000msec. 7. The group label can have one of 4 different values: 1 (b-group), 2 (m-group), 3 (e-group), or NIL (no group). When EPAM rehearses a group, it rehearses all the items in the loop with that label. 8. For each auditory loop printout, indicate which group has just been rehearsed. C. Backwards memory strategy. When subjects are asked to report the list starting from the last item, the serial position curve changes. Run a simulation of this phenomena. 1. Turn auditory loop printing off again. (Choose "Imagery Stores" from the "Printing" menu). Make sure that all other printing is also off (i.e., none of the options in the "Printing" menu gave v next to them). 2. Run the visual backward experiment 20 times with a list of 10 words. This is done by choosing the "Visual Backward" option in the "Simulations" menu. Enter 20 for the number of repetitions, and 10 for the number of words. 3. This time EPAM rehearses the groups in the reverse order (e-group, m-group, b-group). 4. Draw the serial position curve as you did in part A using this new data. 5. Turn auditory loop printing on again. (Choose Turn Imagery Updates On" from the "Print" menu.) 6. Run the experiment once again by choosing "Visual Backward" from the "Simulations" menu and enter '1' for the number of repetition and 10 for the number of words. 7. For each auditory loop printout, indicate which group has just been rehearsed. 8. Is the serial position curve different this time? Explain why this is so. 9. What does this say about the cause of the primacy effect in the normal recall condition (when words are to be recalled in forward order)?