Abstract # 50:

Scheduled for Saturday, August 26, 2017 06:00 PM-08:00 PM: (National Ballroom AB) Poster Presentation


WHAT PRIMATES FORGET REVEALS HOW THEY REMEMBER: SEQUENCE-LEARNING ERRORS MADE BY APES (GORILLA GORILLA GORILLA) AND MONKEYS (MACACA FUSCATA) SUPPORT THE ORDINAL MODEL OF SERIAL LEARNING

L. M. Hopper, C. L. Egelkamp, K. A. Cronin, S. L. Jacobson, K. E. Wagner and S. R. Ross
Lincoln Park Zoo, Lester E. Fisher Center for the Study and Conservation of Apes, Chicago, IL 60614, USA
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The ability of primates to remember sequences is well documented. Less understood is what sequence-learning errors reveal about primate memory. Five gorillas and seven macaques, socially housed at Lincoln Park Zoo (Chicago, IL), were tested on a touchscreen serial-learning task. Subjects had to select symbols in a pre-determined order. After learning a two-item list (A-B), a third symbol (C) was added. When presented with the 3-item list, 31.1% of the subjects’ first 30 trials were correct on average. Rate of successfully sequencing the symbols varied by subject (P<0.001) but not by species or trial (both P>0.05). Success rate (mean=58.9%) was positively associated with selecting symbol A as the first list-item (P<0.001). However, in these trials subjects only subsequently chose symbol B, rather than C, at chance (mean=53.1%), with no variation across subjects (P>0.05). This suggests a failure to encode the last item (B) in the previously-learned sequence (A-B). The responses of one gorilla, who learned 4-, 5-, 6-, and 7-item lists, revealed the same encoding error: when he correctly sequenced n-2 items, he chose penultimate symbol at chance (mean=44.5%), with no effect of sequence length (P>0.05). The primates’ failure to encode the last item in a sequence, as revealed when a novel symbol was added in the ultimate position, supports the ordinal model of serial learning, such that encoding strength decreases by list-item position.