Discrimination, contrast, and chaining effects of prior training without discriminanda and response-contingent delay of discriminandum presentation

Administered 2 groups of 32 male albino Sprague-Dawley rats differential conditioning in a discrete-trials lever-pressing situation following either minimal or extended amounts of consistently rewarded pretraining in the absence of either discriminandum. On random trials, presentation of the discriminandum was delayed until various numbers of the required responses had occurred. Extensive pretraining resulted in more rapid development of differential responding and higher asymptotic response speeds to both discriminanda. Positive behavior contrast was relative both to conventional, predifferential base lines and to those provided by responding during absences of discriminanda in differential conditioning. Little evidence was found for losses in discriminative stimulus control when the discriminandum presentation was delayed until after responding had begun. Results are discussed in the context of frustrative nonreward theory and the response chaining hypothesis.