Stimulus generalization as a function of the delay between training and testing procedures: a reevaluation.

Three groups of 12 pigeons each were trained to discriminate between lights of 550 mmu (S(D)), correlated with 1-min variable-interval reinforcement and 570 mmu (S(Delta)), correlated with extinction. Group A was tested for wavelength generalization in extinction 1 min after meeting the discrimination criterion; Group B was tested 24 hr later; Group C was tested 24 hr later after a 3-min (reinforced) warm-up with the S(D). The post-discrimination gradient of Group B was significantly flatter and showed significantly greater area shift than that of Groups A and C. The gradient of Group C was similar to that of Group A, indicating that the warm-up eliminated the effect of the delay period.