Solving XOR

Abstract

Three experiments examined the way in which exclusive-or (XOR) problems are solved by rats. All rats first received food-rewarded positive and negative patterning problems with two stimulus sets: either A+, B+, AB- and C-, D-, CD+, or A-, B-, AB + and C+, D +, and CD-. Subsequently, rats received revaluation trials in which A was paired with shock and C was not, prior to generalization test trials with B, D, AB, and CD (Experiments 1 & 2); or received A-->shock trials prior to tests with B and CD (Experiment 3). There was greater generalized fear to B than to either D (Experiments 1 & 2) or AB (Experiment 2) and CD (Experiments 2 & 3). These results are inconsistent with configural, connectionist models, but are consistent with an alternative connectionist model that can represent the logical structure of XOR problems.