LEARNING: OPERANT CONDITIONING AND VERBAL LEARNING.

cumulated data. The theorist must wait until late in this process for interest­ ing principles and structure ; meanwhile, he is repelled by a forbidding thicket of data. Such a field is difficult to review, too. This brief resume concentrates on certain relatively structured areas. It touches others lightly, but runs out of space without even mentioning a number of important prob­ lems or !1Undreds of worthy experiments. We need a book on the subject, at least. Fortunately, we were in the process of getting one at the time of this writing: OPerant Conditioning and Psychology, edited by Honig (51). Operant research, as intended by this review, includes roughly those studies that measure the rate or relative frequency of a freely repeatable response. Branching from this core are methods that restrict response free­ dom in some way, or that record response variables other than rate. Skinner's insistence on the rate measure (84) has been amply justified, but, as he re­ cently reiterated (86) , it is ultimatel y response probabi lit y under given con­ ditions that we wish to predict. Experimental analysis is moving in this direc­ tion, breaking down the indefinite period of time implied by "rate" into short time segments. One reason for this shift has been the gradual recognition 1 The survey of the literature pertaining to "Operant Conditioning" was con­