<p>Evans’ work in Schematic Concept Formation suggests that when over­determined stimuli are involved, the subject is able to learn conceptual schemes without feedback using only information derived from the stimuli (histoforms) themselves. The experimental paradigm involving “same” and “different” responses to stimuli permits the acquisition of the scheme. This scheme is an internal representation of the proto­type which gave origin to the stimuli to which the subject was exposed and which he acquires in the course of the trials. The results of this study suggest the hypothesis that the scheme, necessary and sufficient to judge histoforms from the same prototype as the “same,” is not always necessary to judge histoforms from different prototypes as “different.”</p>