The contingency symmetry bias (affirming the consequent fallacy) as a prerequisite for word learning: A comparative study of pre-linguistic human infants and chimpanzees.

Humans are known to possess an "affirming the consequent fallacy," which assumes that a learned contingency holds true even when the order is reversed. In contrast, non-human animals do not fall for this fallacy, as they do not have the contingency symmetry bias. Importantly, language is founded on the symmetrical relationship between symbols and referents, and the contingency symmetry bias plays a key role in word learning. A critical problem for the ontogenesis of language is whether the contingency symmetry bias has been acquired through the experience of word learning or if it is present before infants begin word learning. Using a habituation switch paradigm, 8-month-old human infants and adult chimpanzees were familiarized with two object-then-movement sequences, whereby Object A (or B) was always paired with Movement A (or B). At test, the order of the contingency was reversed. The infants showed surprise when observing the violation of the object-movement pairings in the reversed sequence (Experiment 1). In contrast, despite the chimpanzees being able to detect the violation of the pairings in the original direction (Experiment 2a), they did not discriminate the learned and novel pairings when the order of the contingency was reversed (Experiment 2b). The results suggest that the contingency symmetry bias is a uniquely human cognitive bias, one which plays a critical role for language acquisition ontogenetically. This contingency symmetry bias likely gives humans a great advantage, by enabling them to rapidly expand their knowledge without direct training and making them strikingly different from other animal species. (250 words).

Physical intuitions about support relations in monkeys (Macaca fuscata) and apes (Pan troglodytes).

Nonhuman primates, like humans, have demonstrated various physical intuitions. Cacchione and Krist (2004) examined chimpanzees' intuitions about support relations with the violation-of-expectation task. They reported that the chimpanzees possessed intuitions about support, but their intuitions differed from those of humans in part; they were sensitive to "contact/no-contact" and "amount of contact" but not "type of contact" rule. To further explore intuitions about support in nonhuman primates, we conducted similar experiments on monkeys (Japanese monkeys) and apes (chimpanzees). In three experiments, we presented physically possible and impossible events of different support relations to the participants and measured their looking times. The results reveal that the chimpanzees and monkeys detect the violations of "contact/no-contact" and "amount of contact" but not "type of contact" variable. Therefore, the apes and monkeys possess similar intuitions; however, these intuitions differ in part from those of humans. The present study provides new and corroborative evidence of intuitions about support in nonhuman primates. However, this again leads to the question of distinctive understanding about support relations among primate species.

Long-term visual recognition of familiar persons, peers, and places by young monkeys (Macaca fuscata).

Five-year-old Japanese monkeys were tested on long-term visual recognition memory. The objects used were those that they had encountered daily during their first 2 years of life as to-be-remembered stimuli: persons, peers, and places. After a 3-year delay, we conducted a recognition test using the preferential looking paradigm where the monkeys were presented with pictures of these familiar stimuli in combination with those of novel stimuli. The monkeys looked relatively longer at pictures of familiar stimuli than at those of novel stimuli, while participants in the control group, who had never seen the stimuli in question, showed no discriminative preference. The monkeys thus recognized the familiar stimuli through the pictures, suggesting retention of visual information on real objects encountered in their lives even after a 3-year delay. Our present findings confirmed long-term visual recognition in monkeys, which might be essential to ecologically and socially significant behaviors such as individual identification.

Can chimpanzee infants (Pan troglodytes) form categorical representations in the same manner as human infants (Homo sapiens)?

We directly compared chimpanzee infants and human infants for categorical representations of three global-like categories (mammals, furniture and vehicles), using the familiarization-novelty preference technique. Neither species received any training during the experiments. We used the time that participants spent looking at the stimulus object while touching it as a measure. During the familiarization phase, participants were presented with four familiarization objects from one of three categories (e.g. mammals). Then, they were tested with a pair of novel objects, one was a familiar-category object and another was a novel-category object (e.g. vehicle) in the test phase. The chimpanzee infants did not show significant habituation, whereas human infants did. However, most important, both species showed significant novelty-preference in the test phase. This indicates that not only human infants, but also chimpanzee infants formed categorical representations of a global-like level. Implications for the shared origins and species-specificity of categorization abilities, and the cognitive operations underlying categorization, are discussed.

Do infant Japanese macaques ( Macaca fuscata) categorize objects without specific training?

In the present study, we examined whether infant Japanese macaques categorize objects without any training, using a similar technique also used with human infants (the paired-preference method). During the familiarization phase, subjects were presented twice with two pairs of different objects from one global-level category. During the test phase, they were presented twice with a pair consisting of a novel familiar-category object and a novel global-level category object. The subjects were tested with three global-level categories (animal, furniture, and vehicle). It was found that they showed significant novelty preferences as a whole, indicating that they processed similarities between familiarization objects and novel familiar-category objects. These results suggest that subjects responded distinctively to objects without training, indicating the possibility that infant macaques possess the capacity for categorization.