Acquisition of a unique cue in positive and negative patterning?

Forty college students received a classical differential conditioning procedure involving both positive and negative patterning, each of these being associated with a different pair of stimuli. In positive patterning, elemental stimuli, A and B, were presented without an unconditioned stimulus while their compound, AB, was paired with electric shock. In negative patterning, elemental stimuli, C and D, were paired with shock while their compound, CD, remained unpaired. Thirty of these subjects then received a negative patterning transfer test on new stimuli, while ten subjects received a positive patterning transfer test. First interval response (FIR) and second interval response (SIR) were measured. During initial acquisition, positive patterning occurred in both dependent measures, but negative patterning was present only in the SIR. The transfer tests showed almost significant transfer of positive patterning in FIR and SIR. Negative patterning showed significant transfer neither in FIR nor SIR. It was concluded that, although elementary models of conditioning can explain positive patterning on the basis of summation of excitation from the elements to the compound, the occurrence of negative patterning in the SIR and the almost significant transfer of positive patterning in FIR and SIR appear to require the additional assumption of a unique cue.