Further investigations of stimulus coding in nonlinear discrimination problems.

Two human Pavlovian SCR conditioning experiments are reported, investigating CS-coding in negative patterning (NP). In Experiment 1, NP was run with two pairs of letter stimuli (C, N, and M, J), reinforced by shock when alone but not in compound. Controls with the same paired-unpaired sequence saw two additional nonreinforced letters (X and H) instead of compounds. The NP group learned the element-compound differentiation, but the controls did not discriminate reinforced from nonreinforced letters. The availability of an abstract rule (such as stimulus number) for distinguishing between reinforced and nonreinforced CSs led to discrimination in NP, but its unavailability resulted in no discrimination in the controls. In Experiment 2, NP was run with one pair of letters (reinforced as elements but not in compound). A control group had the same paired-unpaired sequence, but their compound contained two different letters from the reinforced ones. The NP discrimination was learned, but the controls failed to differentiate the reinforced elements from the nonreinforced compound. It was concluded that the NP discrimination was not based on the number of reinforced and nonreinforced stimuli, because this dimension was available to both groups in Experiment 2. The abstract dimension of separate versus together, on the other hand, was available only in NP, suggesting that it is the SINE QUA NON for the acquisition of the kind of NP discriminations we have been studying.