Subjectively, the types differ in degree of vividness and degree of autonomy, or independence from control by the subject. Objectively, they differ in the preceding and antecedent conditions of their occurrence. One of the principle tasks of psychology, in Richardson's view, is to find correlations between measurements for various types of imagery and other psychological variables. The degree of vividness of various imagery types, for instance, could be correlated with efficiency in memory tasks, sports performance, effecatiousness of psychotherapeutic exercises, problem solving abilities, and numerous other variables of interest. The philosophic interest in classification is that it provides a basis for phenomenological description and philosophic distinctions using an agreed-upon terminology.
Classification serves to identify the topic of philosophic inquiry.
This exercise shifts the focus of our inquiry into the nature of imagery away from models of explanation based on unknown mechanisms and toward description of the phenomena. From his review of what was known about imagery at the time, Richardson concluded that we simply do not know what part imagery plays in determining our behavior and other psychological processes, but that it played some part he thought was nearly certain. Richardson suggested that the principal problem in determining the role of imagery was the problem of measuring imagery. His understanding of measurement for psychological entities is entirely different from Kosslyn's. Richardson accepted the reports of imagery given by subjects at their face value.