Presentation Factors in Discrimination Learning by Chimpanzees

Abstract

During the course of studies of response variability and other age related factors in adult chimpanzees of various ages, several methods of stimulus presentation were tested. Vertical and horizontal presentations, different types of stimulus blocks, and the presence of an additional positive object using a threehole test tray were examined in a series of discrimination problems. METHOD Subjects Sixteen adult chimpanzees ranging in age from 11 to 40 years were used in each of the two situations described. Procedare In the first experiment, two different positive (indicating a baited food well) objects and a negative (indicating an empty food well) object covered a food well on a three-hole test tray. Novel objects were substituted systematically on 12% of the trials for one or both of the positive objects, or only for the negative object. Novel objects assumed the reward value of the objects they replaced. A total of eight sessions of 100 trials each were completed by each chimpanzee. In a second experiment, 10 conditional discrimination and discrimination reversal problems were presented on two-hole test trays. Both vertical and horizontal presentations were used. Simple uni-color blocks, typical laboratoryfabricated multidimensional blocks, and blocks identical in all respects except for the presence of differently cut and patterned wallpaper figures glued on them, were used as the stimulus blocks. All problems were presented until the criterion of 10 consecutive correct responses was achieved on the initial discrimination and on the reversal. For contingency problems, two errorless reversals or changes were required, each defined by 10 initial correct responses.