Hierarchical complexity in stone-tool use by wild chimpanzees and nesting-cup manipulation by captive chimpanzees

Misato Hayashi, Primate Research Institute, Kyoto University, Japan

A group of wild chimpanzees in Bossou, Guinea, West Africa, use a pair of stone as hammer and anvil to crack open oil-palm nuts. Sporadically, chimpanzees use a wedge stone to stabilize the upper surface of an anvil stone. The use of wedge stone is categorized as Level-3 in the Tree Structure Analysis proposed by Matsuzawa (1996) showing the maximum hierarchical complexity in wild nonhuman animals. Captive chimpanzees can combine up to nine cups into a nesting structure. Although the combination process is mainly based on trial-and-error strategy, the most advanced subassembly-method occurred and may contribute to achieve efficient nesting.

Imitation of human music in a parrot species

Yoshimasa Seki, Department of Psychology, Aichi University, Japan

The cockatiel, a parrot species, is one of the most popular companion birds. It is well known that they imitate various human music with their whistle-like vocal sounds among aviculturists. I raised some cockatiel chicks that were exposed to human music played with my whistle. Three birds were spontaneously getting to imitate the whistle sound. Moreover, they occasionally joined in my ongoing whistling and synchronized their vocal timing with the whistle sounds. This suggests that they learned, not merely chain of the sound notes but, a global melody of the music which has a hierarchical structure.

Animal songs before emergences of hierarchical structures

Hiroki Koda, Primate Research Institute, Kyoto University, Japan

Animal songs have been comparatively tested with the human language syntax, and most researchers have believed that the critical lacks of hierarchy organizations were a key component to divide animal songs from our language syntactic rules. Here I talked our recent progress of grammatical analysis of ape songs, i.e., gibbon songs. Together with the evidence of birdsong syntax, I will attempt to discuss a possible evolutionary causation to provide only us a hierarchy complexity.

Evolution of cognitive capacities accounting for hierarchical complexity in music

Rie Asano, Department of Systematic Musicology, University of Cologne, Germany

Music is hierarchically structured and its complexity in terms of Chomsky hierarchy corresponds to that of context-free language. My talk discusses ways to link such abstract theoretical models of cognitive capacities to cognitive and neural processes within a comparative biological framework. I explore the application of formal grammar theory in current empirical comparative research on the language and music capacity, propose a comparative approach putting more focus on cognitive and neural processes by focusing on musical rhythm and the cortico-basal ganglia-thalamocortical circuits, and draw implications for the evolution of capacities accounting for hierarchical complexity in music, language, and action.

Populating the Chomsky hierarchy

Cedric Boeckx (1,2) and Pedro Tiago Martins (2), (1) ICREA & (2) UB-Institute of Complex Systems, Univeristat de Barcelona, Spain

In this talk we will examine, from a comparative perspectives, the factors that enter into the capacity to process more complex hierarchies (described in the light of the Chomsky hierarchy of formal languages), starting with differences between "phonology" and "syntax". This will lead us to discuss differences among non-human vocal learners, and, more tentatively, hominins.

Gradually evolving limited merge

Sverker Johansson, Dalarna University, Sweden

Chomsky and others regard unlimited Merge as the defining feature of language, that cannot evolve gradually. The neural implementation of Merge is not well understood, but must involve something functionally equivalent to pointers in working memory. Every Merge requires two pointers, and full syntactic trees may require dozens. Other syntactic paradigms also need pointers. Humans do hierarchies in general better than chimpanzees. Any hierarchical thinking requires nested pointers in working memory, but they are neurologically expensive and degrade with depth. Humans have larger working-memory capacity than chimpanzees, which has been proposed as key to human cognitive evolution. Gradual evolutionary growth of pointer capacity will allow gradually increasing syntactic complexity, without saltations in the underlying computational machinery. Both depth degradation and pointer capacity naturally limit Merge even in modern humans, consistent with corpus data.

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