Abstract
Using methods comparable to those used previously to test closely-related taxa (Pan troglodytes and Macaca mulatta), our aim was to better understand how gorillas (Gorilla gorilla gorilla) and Japanese macaques (M. fuscata) learn sequences. Using a disappearing-type simultaneous chain, we trained five gorillas and eight macaques on a two-item list of colored stimuli presented via touchscreens. There was no difference across species in the number of trials required to learn the two-item list. We added a third item to the list as each subject reached criterion. We then analyzed the subjects’ first 30 trials with the three-item list and found that the rate of successfully sequencing the list varied by subject but not by species. In their first 30 trials of the three-item list, subjects selected the second item correctly only at chance, suggesting they had only encoded the first symbol when learning the two-item list. One gorilla, tested on longer sequences, showed similar responses: when first presented with a newly-lengthened list, he only selected the penultimate item at chance levels. Thus, the primates’ errors with newly-lengthened lists is suggestive of the chaining theory of learning. These results highlight similarities in list learning of these two distantly-related primate species as well as the clear intra-species variation in learning.
Highlights
Using methods comparable to those used previously to test closely related taxa ( Pan troglodytes and Macaca mulatta), our aim was to better understand how gorillas (Gorilla gorilla gorilla) and Japanese macaques (M. fuscata) learn sequences
Much is known about the sequence-learning abilities of several nonhuman primate species (e.g., Judge, Evans, & Vyas, 2005; Matsuzawa, 1985; Ohshiba, 1997; Ross, 2009; Swartz, Chen, & Terrace, 2000), yet we still know little about the strategies with which certain species of primates recall sequential information
We presented western lowland gorillas and Japanese macaques with a sequencing task to better understand how these species responded to a modified version of a previously learned sequence, how the errors they made reflected their memory for the original list, and how their response latencies reflected their decision-making certainty
Summary
Using methods comparable to those used previously to test closely related taxa ( Pan troglodytes and Macaca mulatta), our aim was to better understand how gorillas (Gorilla gorilla gorilla) and Japanese macaques (M. fuscata) learn sequences. Building on the early work of Ebbinghaus (1964), who studied human memory, comparative psychologists have tested the relative strength and flexibility of nonhuman animal serial memory (e.g., Fountain & Benson, 2006; Merritt, MacLean, Jaffe, & Brannon, 2007), often using the simultaneous-chaining paradigm (Terrace, 1984, 1993, 2010; Terrace & McGonigle, 1994) In such tests, the subject is presented with all the possible stimuli in the list and must select them in a predetermined order. We selected these species to allow for comparisons with other commonly tested primate species (Pan troglodytes and M. mulatta: Beran et al, 2004; Chen, Swartz, & Terrace, 1997; Matsuzawa, 1985; Terrace, Son, & Brannon, 2003)
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