Abstract: Ten adolescent, experimentally normal primates-2 Macaca nemestrina,2Macaca speciosa, 2 Macaca assamensis, 1 Papio hamadryas, 1 Mandrillussphinx, 1 Nycticebus coucang and 1 Cebus albifrons-were used. Reversallearning wasstudied by the method of simultaneous presentation of positiveand negativestimuli. All testing was carried out with a modified WGTA. Tr-aining commenced, with each S to reach a criterion of 80%correct in 2-3successive trials of "stereotype". Next, the "stereotype" was reversed, untilS again reachedthe same criterion. The major findings were: (1) There was no fundamental distinctions in the mobility of the nervousprocesses of Macaca nemestrina, Macaca speciosa and Macaca assamensis, buttheir mobilities were superior to that of Nycticebus coucang. (2) Our results show that the reversal of color stimuli was more diffi-cult than the form stimuli in all of primates tested. (3) The difficulty of reversal from positive to negative stimuli was thesame traits in the majority of primates tested.

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