In these experiments Ss were asked to discover rules of discrimination which involved logical conditions among visual primitives in the stimulus set. The introduction of logical relations into concept attainment tasks reflected a belief in the general relevance of logical informational structures. Each stimulus dimension was a priori semantically equivalent. Tasks focused on the identification of the exact logical rules for combining stimulus values to define a category. The concept to be acquired was a logical condition which would obtain (be true) for all items within a category and for no others. In contrast to the structure of Hull's task, visual perception.