The present experiments were aimed at identifying the interactions among atomistic and configural processes in governing response acquisition to a compound stimulus and its components. To that end, the acquisition of the rabbit's nictitating membrane response was examined in (a) "stimulus compounding," which entailed reinforced training with two separate stimulinamely a tone and a light-plus tests with a compound of the two stimuli, and (b) "negative patterning," in which reinforced presentations of the separate stimuli were interspersed with a large number of unreinforced compound presentations. In Experiments 1 and 2, stimulus compounding produced summation effects-that is, a higher level of responding to the compound than to either component stimulus. In the negative patterning schedule, responding to the unreinforced compound declined as a direct function of the stimulus duration, which was varied across values of 300, 800, 1,300, and 1,800 ms in a delay conditioning paradigm. Experiment 3 demonstrated that a negative patterning outcome emerged only when the duration of both the components and the compound was relatively long, for example, 1,800 ms. Together the results support a "unique stimulus hypothesis," which contends that responding to a compound is jointly governed by coexisting representations of a compound and its components. Furthermore, the compound representation appears to require more time to recruit than do those of the components.

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