LEARNING: VERBAL, PERCEPTUAL-MOTOR, AND CLASSICAL CONDITIONING1
Ronald S. Lipman
Jensen's ( 1960) observation that individual difference variables have been neglected in the search for laws of learning seems less accurate now than it was a few years ago, particularly with regard to intellectual variables. Since McPherson's ( 1958) review of the 14 studies, published in the decade between 1948 and 1958, which investigated learning of retarded Ss, there has been a marked increase in research in this area, the main focus of which has been on comparing the performance of retarded and normal Ss on different learning tasks. The basic aim of these comparisons is, of course, to identify the learning deficits which characterize the retarded. However, as Hilgard ( 1951) has stressed, learning per se is a permissible inference from performance only when such factors as motivation, fatigue, drug effects, and maturational changes have been controlled. Since Zigler ( 1962) has indicated that differing histories of social deprivation in retarded and normal Ss may result in differences in motivation, inferences about learning drawn from performance differences are highly tenuous.
Caution is also necessary in generalizing from the results of particular studies in view of the heterogeneity of the retarded population (exogenous versus endogenous; institutionalized versus noninstitutionalized) and the real possibility of interaction between different intelligence levels and task difficulty. The general finding that no single g factor will account for the variance across different learning tasks ( Hovland, 1951, p. 635) or, for that matter, within a subarea such as classical conditioning should also be noted.
Denny ( 1963) has suggested a useful approach for identifying learning____________________