Barker also develops a useful analogy for conceptualizing this relation, as well as preparing readers for later claims about behavior settings. He observes that 'molar behavior' is to the 'ecological environment', just as 'visual perception' is to 'light'; i.e. in order to understand visual perception, you have to understand light, independent from visual perception. If we were only to look at the eye-optic channel at the instant that light hit the receptor surface, we would know nothing of depth of field, focus, or perspective.