In Skinner's analysis of verbal behavior, three categories of environmental control over instances of verbal behavior appear to be relevant to the study of infant vocal development: the mand, the tact, and the echoic categories. Procedures used in the remediation of language deficiencies and procedures found in work in the area of language…

Recent literature on the acquisition of "more" and "less" is reviewed with special emphasis on some key issues. The overriding goal of studies in this area has been the discovery of the developmental sequence that the child follows in acquiring "more" and "less," and, more generally, all comparative structures. The earliest empirical studies on…