15-883 Homework #5
Computational Models of Neural Systems
Issued: April 9, 2001. Due: April 16, 2001.
How to Run the Rescorla-Wagner Simulator
You should cd to the directory matlab/rescwag, or download the file
rescwag.zip and unzip it. When you're ready to begin, type "matlab"
to start up Matlab. Then type "run" to start the simulator.
What the Simulator Does
The simulator offers three conditioned stimuli: cs1,
cs2, and cs3. In addition, there is a background
stimulus bkg that is always on. A "trial" is defined as a set
of zero or more conditioned stimuli paired with either a US or no US.
By setting the pushbuttons you can define trials as you wish.
Clicking on the associated "train" button runs the trial and updates
the weights according to the Rescorla-Wagner learning rule. The
buttons are organized as two groups of five trials each, and each
group has an "all" button that will train on all the trials in that
group.
Problems
For each of the problems below, create an appropriate set of trials,
train the model, and then print out the window. You can print the
screen to a file by typing print -deps -r300 myfile.ps. Make a
separate printout for each problem; these are what you will hand in.
- Demonstrate blocking. Use one line in the first group of five
trials to train on CS1 paired with the US. Note that if you just
click on the "train" button for that line, both the CS1 and BKG
weights grow. You will need to mix in some trials with no stimuli
(but of course BKG will still be present) in order to train the model
correctly. (If you use the "all" button for this group you will
include some of these empty trials.) Then, use the second group of
five trials to train on CS1 and CS2 paired with the US.
- Demonstrate overshadowing. You will need to modify an alpha variable
to make one stimulus more salient than the other.
- Demonstrate learned inhibition.
- Demonstrate extinction of a conditioned response.
- Demonstrate failure to extinguish a conditioned inhibitor. (You
will need to select the option that prevents negative CRs in order for
this to work.)
- Demonstrate the effect of partial reinforcement, where the CS is
paired with a US half of the time, and no US the other half of the time.
Dave Touretzky
Last modified: Mon Apr 9 05:51:20 EDT 2001