Simple sensory systems give an idea of how information is coded in nerve activity. First, we will look at a a stretch receptor and see that more stimulus produces a larger receptor potential and a higher FREQUENCY of action potentials. (Eckert, Fig. 7-4c)
- The Frequency of action potentials varies as the log of the stimulus intensity! (Eckert, Fig. 7-8b) This logarithmic dependence is a consequence of the statistical nature of the generation process of the receptor potential, a point we will come back to when we discuss vision at low light levels. (Eckert, Fig. 7-8a - panel 3)
- The same processes of detection of stimulus intensity that predicts the logarithmic dependence of response of the nervous system leads us to understand how statistical error in detection of a stimulus, say light intensity, varies with the intensity of the stimulus. Statistical error limits the differences we can detect, say an increase in light intensity from one part of an image to another. We'll discuss the relationship of statistical error to the Weber-Fechner law and return again to this point when we discuss vision at low light levels. Important - take good notes on this discussion.
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