A functional analysis of receptive language and productive speech: acquisition of the plural morpheme.

Operant conditioning procedures were applied to two retardates to establish receptive auditory plurals: correct pointing to single or paired objects was reinforced after hearing singular or plural labels. This training proceeded until an errorless (generative) criterion of correct performance was achieved. Unreinforced probes measuring expressive use of singulars and plurals were interspersed in this receptive training. Neither subject generalized from this receptive training to expressive plurals, in that each used singulars when labeling pairs. Then, both subjects were directly trained in conventional expressive plurals to an errorless (generative) criterion. The previous design was then repeated, but the receptive repertoire was reversed: pointing at pairs in response to singular labels was reinforced, and vice-versa. Unreinforced probes of expressive plural usage again showed its independence of the current receptive repertoire in that conventional (unreversed) plural usage was displayed. Thus, the independence of the expressive repertoire (even when unreinforced) from the reinforced patterns of the receptive repertoire was demonstrated.