Since much of AI is about the best way to represent information, you should go to the exam armed with examples of representations and their properties in both computing and psychology. Once you grasp the idea, you will be able to pick them out of the psychology you know and the rest of the AI course.
For the essay, you can concentrate on those used by Evans' program. In case you want other examples, now or later, here are some more references. Try to read them sometime during the course (not necessarily this week).
This is an example of AI as cognitive modelling. The authors have examined the games of Go and Go-Moku, and suggested what mental representations players might develop for scanning the boards in the most efficient way to detect attacks, winning positions, etc. (The games' rules are completely different, and a good scan for one game would not help with the other). They report experiments for testing their suggestions, and a computer program for modelling these representations.
Chapter 7 deals with the difference between symbolic and analogue representations --- the latter include diagrams --- and why symbolic representations are sometimes less useful than analogue ones. He shows that you can't draw a clear distinction --- some representations may be both at the same time.
Chapter 8, especially sections 8.1, 8.3 - 8.10, and 8.16, is an account of the kind of representation that might build up in a child learning to count. This is how cognitive psychology ought to answer questions like ``Why is it easier to count forwards than backwards?''.