Concept learning with differing sequences of instances.

Under conditions where several concepts are learned concurrently and concept instances are presented successively, the instances of any given concept may be presented in varying degrees of proximity to one another. At one extreme these may be presented one after the other without the interpolation of instances of any other concept, and at the other extreme two instances of a given concept may never occur in succession without the interpolation of one or more instances of other concepts. The present investigation concerns the rate of concept attainment under these two modes of presentation of concept instances. Theoretical considerations advanced by Underwood (6) suggest that the first condition in which the instances of a given concept are presented in close proximity should produce more rapid learning. This expectation is based upon the assumption that to abstract the common property or properties of several concept instances, perceptual, ideational, or motor representations of the properties of these instances must occur contiguously. The implicit representation may be either in direct response to the presentation of a concept instance or recalled from the past presentation of an instance. When two concept instances are presented simultaneously, occurrence of perceptual representations of the relevant stimulus properties will depend primarily upon factors of set or attention; when the instances are presented successively, the additional factor of memory is introduced, so that, even though the relevant properties of a first instance are perceived at the time of presentation, they may be forgotten in the period intervening before the presentation of a second instance. The likelihood of forgetting would be expected to be a function of such factors as the complexity of the original instance, the length of the intervening period, and the nature of the activities interpolated during the period. The conditions employed in the present experiment and those employed in a recent study reported by Hovland and Weiss (4) may be regarded as bracketing adjacent segments on a continuum of conditions facilitating to varying degrees the contiguous perceptual representation of concept instances. In the study of Hovland and Weiss, learning with simultaneous presentation of concept instances was compared with the theoretically less favorable condition of successive presentation of instances, and a significant difference was obtained in the expected direction. In the present study a condition similar to the successive condition of the Hovland and Weiss study was compared with the theoretically still less favorable condition in which concept instances were not only presented successively but were also intermixed with instances of other concepts. In this method of presentation, at the time of presentation of an instance of a given concept, retention of earlier instances of the same concept would be expected to be impaired both by