With only a handful of physicians in this large audience, I find myself in a rather pre-carious position trying to relate a complex topic to a group of scientist primarily from the physical sciences. Perhaps I can make an analogy. We spent a significant amount of time this morning elaborating on signal to noise ratio. If one looks at the spectrum of signal to noise ratio, in trying to quantitate factual information regarding the physical sciences on one hand and the biological sciences, particularly medicine, on the other, the results are rather interesting. There is no question in my mind, having spent a few years in physics, that the signal to noise ratio in the physical sciences is quite high. As one approaches the biological sciences, it diminishes significantly and as one approaches medicine it becomes quite small, particularly in fields such as psychiatry where information is extremely difficult to quantitate. The reason for this is relatively simple; in physical sciences an equation needs to be solved, an integral needs to be worked out or mathematical postulate is either proven or not proven. However, as one approaches biological systems, the number of variables, one depending on another, sometimes almost appears infinite. Therefore, to try to take some of these physical measurements, used in the day-to-day analysis of mathematical equations, etc., and use these tools and each of the variables in our biological systems sets up an extremely complex situation to solve. Therefore, for me to talk about the psychophysics from a physician-radiologist point of view is somewhat presumptuous on my part. However, our challenge in medicine today is to use the tools of the physical sciences to better quantitate these variables and it is for this reason that I appear before you today.