Four experiments used an autoshaping procedure with pigeons to investigate the basis of configural discriminations. The elements of both a negative patterning (A+, B+, AB-) and a conditional discrimination (AC+, BD+, AD-, BC-) were paired, in a second-order procedure with two new key lights, X and Y. Responding was then tested to X and Y presented in compound with each other and with A and B. The pattern of responding to compounds containing X and Y was like the pattern of responding to compounds containing their associates, A and B. This suggests that A and B can be replaced by their associates without disrupting responding to their compounds. Because X and Y are physically different from A and B, this in turn suggests that any unique cue controlling responding to their compounds does not depend on the physical presence of the component stimuli. Instead the unique stimulus appears to arise from the joint activation of memory representations.