Today I am talking about the effect of common noise sampling variability on psychophysical experiments. I became interested in this problem when I was considering the trade-offs involved in determining the size of my signal sets for my thesis experimentation. I chose to talk about it today because it is a problem we all come up against when doing psychological experimentation. But before I get into sampling variability itself I will put you into context by talking about noise in general and how it is modeled in psychophysics.