The effects of five to six weeks of social isolation after weaning on the open-field behavior of ICR male mice were examined using a direct observational method. Except for two behavioral components, namely, stretching and grooming, the isolated and grouped animals showed similar behavioral changes in the 10-min open-field test. The rate of decrease of stretching in the first four minutes was significantly lower in isolated than in grouped animals. Grooming significantly increased in the last four minutes in isolated animals but not in grouped animals. These results suggested that the deprivation of social experiences during a juvenile period might enhance anxiety or stress responses and inhibit habituation in a novel environment.

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Thirty-two rats were divided into dietary restricted or ad libitum feeding groups at 70 days of age in order to examine the effects of short-term dietary restriction on performance of the Morris water maze task (a reference memory task) and delayed-matching-to-place (DMTP) task (a working memory task). The dietary restricted rats were kept at a body weight of 280g throughout training. When they reached 93 days old, behavioral training was initiated. Half rats from each group were trained with the water maze task first, followed by the DMTP task, and the other rats in the reversed order. Regardless of the order of the tasks, dietary restriction had no effect on performance on the water maze task. In the DMTP task, restricted rats performed significantly poorer than ad lib rats at 30 minutes delay, but not at 30 seconds delay. These results suggest that dietary restriction has no effect on reference and working memory tasks when the memory load is light, but it causes impairment on the working memory task when the memory load is heavier.

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Four goldfish (Carassius auratus) were tested in an aquatic version of the eight-arm radial maze equipped with intra-maze cues. The fish received forty trials of free-choice task training followed by a test in which intra-maze cues were removed. As a result of training, the fish entered approximately 6.9 different arms in the first eight choices, and this score was significantly higher than the chance level. Any stereotypic response pattern, especially a tendency to enter adjacent arms in a rotate style, was not observed. In the test, choice accuracy deteriorated to the initial level by removal of intra-maze cues. These results suggest that goldfish can acquire a radial arm maze task by utilizing intra-maze cues.

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Early experimental accounts of learning assumed that reinforcement strengthened associative bonds whereas nonreinforcement weakened them. Strengthening-weakening models explain the adjustment of nonmammalian species to downshifts in incentive magnitude, but fail to explain a mammalian phenomenon known as successive negative contrast (SNC). In SNC, exposure to incentive downshift leads to poorer performance than that of unshifted controls. SNC forced the development of new learning models emphasizing the acquisition of expectancies and the induction of emotional responses when expectancies are violated. Comparative research suggests a distinction between allocentric learning (tracking changes in the environment) and egocentric learning (remembering the emotional response to environmental changes). Recent research shows that egocentric learning in the SNC situation is modulated by the opioid system. Similar modulation is observed in situations involving physical pain, fear, and social exclusion. An evolutionary hypothesis about the evolution of egocentric learning mechanisms suggests deep connections between the brain circuits controlling fear, frustration, and possibly grief.

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Comparative cognitive science aims to study cognitive abilities of various animals that evolved to fit various natural and social environments. By doing so, comparative cognitive science aims to understand uniqueness of Homo sapiens. However, the faculty of language, as it is so much unique to humans, has been out of the focus for comparative cognitive science. Here we suggest a pre-adaptationist approach to the biological origin of human language. In this approach, language is divided into several sub-faculties and each of these sub-faculties is approached from comparative cognitive science. In this symposium, we selected three subjects: Production and perception of behavioral sequence, tool-use and acquisition of symbolic representations, and three-term social relations. Based on these presentations, discussions are provided by researchers in linguistics and in evolutionary psychology.

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An ability to generate and recognize time-series signals should be one of the most important pre-adaptation to language, because such ability is a basis for syntactical manipulation in language. Examples in birdsong, statistical segmentation, and complex behavioral sequencings were discussed. Common neural substrates for these behaviors and also for human language include the prefrontal- basal ganglia loop for motor sequencing. This loop circuit might be polished up by sexual selection in which arbitrary behavioral sequences can have adaptive value by being selected by hetero-sexual individuals. Thus, sexual selection of the prefrontal-basal ganglia pathway might be a key feature for emergence of language.

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When considering the evolutionary origin of language, we should attend to the social-cognitive aspects of language acquisition in addition to the linguistic competence. This view is an emphasis of Bruner's “Language Acquisition Supporting System (LASS)” and recently intensively studied from the comparative-cognitive-developmental perspective. In this article, I summarize the research project of cognitive development in chimpanzees at the Primate Research Institute, Kyoto University (CDC2000), with special reference to the development of social cognition. During the early infancy, chimpanzee infants showed developmental trajectories similar to human infants. Especially, the chimpanzee infants established close dyadic relationship with their mothers on the basis of mutual gaze and social smiling. However, triadic interactions on the basis of sharing attention, more important social interactions for humans, were not observed in chimpanzees even at their juvenile period. This difference in social interactions between humans and chimpanzees may be the source of more critical difference in the understanding of others. Furthermore, the problem of “enculturation” is also discussed in relation to Vygotsky's concept of “zone of proximal development”.

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Pre-adaptationist approach to the origin of language enables it possible to study the origin of language from the perspective of comparative cognitive science. What are necessary for this field to be productive and scientifically sound? Discussion was led by comments from an evolutionary psychologist and a linguist. An idea of “masking and unmasking” as proposed by Deacon, was introduced to account for several phenomena explained in this symposium. For example, masking of species-recognition in domesticated bird might have resulted in unmasking of song syntax. Masking of several sensory abilities including rote memories necessary for wild life might have resulted in unmasking of symbolic conceptual representation. Masking of wild knowledge might have resulted in unmasking of social knowledge, and masking of two-term relationship might have resulted in unmasking of three-term social relationship.

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