Preliminary Evidence of Relational Same/Different Discrimination of Simultaneously Presented Visual Stimuli in Rats: a Pilot Study

This study examined same/different discrimination of visual stimuli in rats. Two identical stimulus-sets, consisting of four pictures in Acquisition 1 and Transfer Test 1, then two pictures in Acquisition 2 and Transfer Test 2, were presented simultaneously in two compartments of a discrimination box. Rats were trained to stay in one of the two compartments, depending on the same/different relationship among the stimuli in the stimulus sets. Two out of three rats learned same/different discrimination of four stimuli and showed significant transfer of discrimination to novel test stimuli. These two rats also learned same/different discrimination of two stimuli and showed reliable transfer of this discrimination to novel test stimuli. Rats' performance to the test stimuli was comparable to that of the training stimuli, even though responses in the test trials were always reinforced nondifferentially, regardless of the type of stimulus set, to avoid trial-and-error learning to the test stimuli. These results suggest that rats can learn same/different relationships among simultaneously presented visual stimuli at a rather abstract level.