Acquisition and memory of sequence order in young and adult chimpanzees (Pan troglodytes)

Abstract

There is no research about age difference in the process of sequential learning in non-human primates. Is there any difference between young and adults in sequential learning process? Six chimpanzees (Pan troglodytes), 3 young and 3 adults, learned the Arabic numeral sequence 1 to 9 by touching the numerals on a touch-screen monitor in ascending order. Initially, the sequence always started with the numeral 1, i.e. 'start-fixed task'. Training began with the sequence 1-2, 1-2-3, and continued sequentially up to 1-2-3-4-5-6-7-8-9. Later, the subjects were introduced to sequences that started with a random numeral, but always ended with 9, i.e. 'end-fixed task'. Performance in the end-fixed task was worse relative to the familiar start-fixed task. After training with various sequences of adjacent numerals, the subjects were given a transfer test for the non-adjacent numerals. The results suggested that all chimpanzees indeed mastered sequential ordering, and although there was no fundamental difference in the acquisition process between the two age groups, there was a significant age difference in memory capacity. Based on their knowledge of sequential ordering, the subjects were then asked to perform a masking task in which once a subject touched the lowest numeral, the other numeral(s) turned to white squares. Performance of the masking task by young chimpanzees was better than that of adults in accuracy and degree of difficulty (number of numerals). Taken together, these data clearly demonstrate a similarity among subjects in the way chimpanzees acquire knowledge of sequential order regardless of age differences in sequential learning. Moreover, they reveal that once knowledge of sequential order is established, it can be a good index used to evaluate memory capacity in young and adult chimpanzees.

Sequential planning in rhesus monkeys (Macaca mulatta)

“…The subjects in the present study, two of Inoue and Matsuzawa’s (2007, 2009) subjects, and Beran et al’s (2004) subjects, were all only able to respond to one or two masked items. In contrast, four of Inoue and Matsuzawa’s (2009) chimpanzees were able to respond to between four and seven masked items.…”

“…In the second phase of training, the paradigm followed that used by Matsuzawa and colleagues (e.g. Inoue and Matsuzawa 2009), with the stimuli disappearing following a correct response. In this phase, the probability of responding correctly by chance to the first item is 0.20, to the second 0.25, to the third 0.33, to the fourth 0.50 and to the fifth item 1.0.…”

“…Beran et al 2004; Biro and Matsuzawa 1999; Correia et al 2007; Inoue and Matsuzawa 2007, 2009; Mulcahy and Call 2006; Ohshiba 1997; Osvath 2009; Osvath and Osvath 2008; Paxton and Hampton 2009; Raby et al 2007; Scarf and Colombo 2009, 2010). One of the most frequently used paradigms is the simultaneous chaining paradigm (Terrace 1984), which has been used to test the planning abilities of a range of species (Humans: Cook and Wilson 2010; Silberberg and Kearns 2009, Chimpanzees: Biro and Matsuzawa 1999; Inoue and Matsuzawa 2007, 2009; Kawai 2001; Kawai and Matsuzawa 2000, Monkeys: Beran et al 2004; Ohshiba 1997; Scarf and Colombo 2009, and Pigeons: Scarf and Colombo 2010). The basic paradigm presents subjects with n number of simultaneously displayed stimuli.…”

“…Matsuzawa and colleagues have also trained six chimpanzees on a ‘mask task’ (Inoue and Matsuzawa 2007, 2009; Kawai and Matsuzawa 2000). On this task, when a subject responds to the first item, the remaining items are covered by opaque white squares.…”

“…It is possible that if Beran et al (2004) had trained their subjects on a touch screen, some of their subjects would have shown performance levels comparable to those of Matsuzawa and colleagues chimpanzees (Inoue and Matsuzawa 2007, 2009; Kawai and Matsuzawa 2000). To address this possibility, in the present experiment, we investigated the planning abilities of four monkeys when the stimuli were presented on a touch screen.…”