The contribution of the rewarded and unrewarded stimulus in two-choice pattern discrimination in the rabbit

Rabbits were trained to discriminate vertical vs horizontal striations. After reaching criterion one of the patterns was randomly replaced by striations oriented at 135 degrees. Other rabbits were trained to discriminate 45 degrees vs 135 degrees striations. After reaching criterion, one of the patterns was randomly replaced by vertical or horizontal striations. It was found that performance remained at the 90% correct level when the unrewarded pattern was present. When this was not the case performance dropped to 60-70% correct. It was concluded that in the discrimination apparatus used in this study, the rabbit's choice is mainly controlled by the unrewarded stimulus.