Cumulative Record. Chapter 10: The Experimental Analysis of Behavior. Quote 27

We often forget that looking at a visual pattern or listening to a sound is itself behavior, because we are likely to be impressed by the more important behavior which the pattern or sound controls. But any act which brings an organism into contact with a discriminative stimulus, or clarifies or intensifies its effect, is reinforced by this result and must be explained in such terms. (p. 157)