ABSTRACT
This chapter presents some physiological data from monkey cones illustrating the nature of response compression and range control. It shows how adaptation principles, together with gain control and response filtering may be used for a quantitative description of contrast discrimination, both for steady and flashed backgrounds. The human visual system is capable of operating over some twelve decades of light intensity. Over this entire range it can nevertheless discriminate minute changes in contrast, provided it is allowed sufficient time to utilise the various adaptation mechanisms at its disposal. Compression results from a saturating stimulus-response relation, as is typical for all neuronal transducer functions. The diminishing return of the response with increasing stimulus strength implies that sensitivity decreases with stimulus level, which is one way of describing adaptation. J. J. Koenderink et al. proposed an adaptation model incorporating a Weber-machine that performs just such an operation, that is, an output that is independent of the input.
