THOUGHT

What animals cannot conceive

"Thoughts without content are empty, intuitions without concepts are blind," wrote Kant is his Critique of Pure Reason. But how does the brain produce these concepts that are the tools of human thought? Cognitive sciences are attacking this question on the border of neurobiology and philosophy.

“The use of language, mathematical logic, or abstract thinking are three basic properties of human cognition that are based on the use of rules.” © CNRS Photothèque/Christophe Lebedinsky
“The use of language, mathematical logic, or abstract thinking are three basic properties of human cognition that are based on the use of rules.”
© CNRS Photothèque/Christophe Lebedinsky
More than in language, should we not seek the specificity of human thought in man's ability to distinguish the sign – i.e. a word, gesture or image – from what it represents? Here, rock paintings in the Serra de Ireri, near Monte Alegre (Brazil). © CNRS Photothèque/Christophe Lebedinsky
More than in language, should we not seek the specificity of human thought in man's ability to distinguish the sign – i.e. a word, gesture or image – from what it represents? Here, rock paintings in the Serra de Ireri, near Monte Alegre (Brazil).
© CNRS Photothèque/Christophe Lebedinsky

Animals are perfectly capable of learning to distinguish concepts. Two American psychologists, Richard Herrnstein and Donald Loveland, demonstrated this in 1964 by teaching pigeons to tap differently with their beaks depending on whether a picture displayed in front of them was a baby or an old man, a man or a woman, seen from the front, from the back or upside down... in short, in the same way as a Homo sapiens. Can we conclude from this that these birds had acquired the idea of what is human? Researchers prefer to describe this work as experiments in ‘concept discrimination' - a term which, according to Denis Mareschal of Birkbeck, University of London (UK), "avoids giving the idea that the animal has conceived and used a concept similar to that used by the experimenter."

For Mareschal, this work suffers from three additional limitations when one seeks to understand the specificity of human thought. First of all, it was directed at birds rather than mammals, despite the fact that the visual system is organised very differently between the two groups. Second, they often took it for granted that human beings could carry out the tasks which the experimenters sought to teach to the animals, which was far from evident. Third, they neglected to look at the ability of human beings with no command of language - in particular babies - to carry out these exercises, whereas there are "many examples in experimental psychology where children who are unable to speak appear to behave more like animals than adults."

Accepted rules

The aim of the Far project that Denis Mareschal coordinates is therefore to look at the rules governing the acquisition of concepts. "The use of language, mathematical logic and abstract thought are three fundamental properties of human cognition which have in common the fact that they are based on the use of rules," he explains in his project presentation.

The forming of these rules is not, however, the only way of thinking that is available to the human brain. In experiments with artificial grammar, which consists of presenting people with a series of apparently meaningless letters which are interlinked by rules known only to the experimenter, some people work hard to discover these rules, while others look for similarities between the words presented to them.

But when asked, the subjects who have succeeded in mastering this artificial grammar all describe the mechanisms they have used. "It may be that these rules are artefacts produced by the fact that we formalise them by using a language which itself obeys rules," Denis Mareschal posits. In the context of Far, he has designed experimental psychology procedures which make it possible to test the learning of rules in the absence of verbalisation.

Abstract language or corporal inscription

"According to the so-called abstraction from language hypothesis, concepts could be derived from the statistical properties of language - words frequently associated with oral use being presumed to be linked to the same concepts. This would explain the existence of concepts that are specific to each different language. But according to another hypothesis, known as the embodiment hypothesis, these come on the contrary from metaphors which extrapolate into the abstract field an idea that perception renders evident in the concrete field." In this way, for Stefano Cappa of Vita Salute San Raffaele University in Milan (IT), the expression "to float a hypothesis" is understood by analogy with the idea of "to float a ship".

How can these two hypotheses be tested experimentally? The teams of the Abstract project that he is leading have opted for an approach that is at once inter-linguistic - comparing English, Hungarian, Spanish and Italian - and multidisciplinary, bringing together experimental psychology, linguistics and neuro - imaging to test out the respective predictions of the abstract language and the corporal inscription hypotheses. According to the first theory, one would expect to observe an activation of the cerebral areas of language during tasks requiring the use of concepts, whereas according to the second, one expects an activation of the sensor-motorial areas.

For these experiments the researchers use lexical decision tests. These measure the speed with which subjects recognise whether a series of letters presented to them does or does not constitute a word. "Until now it was believed that performance was always better for concrete than for abstract words," Stefano Cappo explains, "but our work is showing that this difference disappears when we take into account the possibility of representing the abstract concept with a mental image."

Alex and signs

More than in language, should we not go looking for the specificity of human thought in man's ability to distinguish a sign - i.e. a word, gesture or image - from what it represents?

This was the hypothesis of the SEDSU consortium, led by Jules Davidoff of Goldsmiths, University of London (UK), which undertook a systematic comparative study of how signs are processed by primates and by humans in the course of their development. In particular, researchers observed that when invited to reproduce a movement of which only an incomplete series of images is given, human beings can do so and primates cannot. Only one chimpanzee, named Alex, achieved this. "The fact is that Alex had not been trained in the practice of language," Jules Davidoff points out. "This shows, in line with our hypothesis, that the understanding of images as signs does not require the command of language." By understanding the meaning of this sequence of images, Alex showed that he had also, in a certain way, acquired a concept of time. This exceptional case should not divert attention from the fact that mastery of this concept appears to be one of the most specific particularities of the thought of our species.

Mikhail Stein

  1. The projects Far (From Association to Rules in the Development of Concepts), Abstract (The Origins, Representation, and Use of Abstract Concepts), SEDSU (Stages in the Evolution and Development of Sign Use), Paul Broca II (The Evolution of Cerebral Asymmetry in Homo Sapiens) and EDCBNL (Evolution and Development of Cognitive, Behavioural and Neural Lateralisation) are part of the European initiative Nest Pathfinder, What it means to be human.

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Left, right in the brain

«© Shutterstock
© Shutterstock

Aleft-hand brain, analytical and logical, involved in language, and a right-hand brain, empirical and intuitive, proces - sing images. This is, put crudely, the concept that neuro-psychologists have today of this human asymmetry. But this functional lateralization is difficult to explain in terms of neuronal circuits. It is to the elucidation of these neuroanatomical bases that the Paul Broca II project in particular is devoted. "As the two hemispheres are roughly identical in volume and mass, the difference needs to come from the shape," explains project coordinator Timothy Crow. "One new idea is that the cortex is thinner and enlarged on one side only." The structural deformation, which is imperceptible to the naked eye but identifiable by computer reconstruction, would then place architectural constraints on the neurons, forcing them to create different circuits in the two halves of the brain.

Another way of understanding the anatomical foundations of cerebral asymmetry is to ask how they evolved. "Although research into this area has been going on for over 140 years, it is only recently that scientists have discovered that this asymmetry is not specific to human beings, as had been thought until then," says Luca Tommasi of the University of Chiti (IT), who is coordinating the EDCBNL project. We now know that the preferential treatment of certain visual or aural information by one hemisphere rather than the other is found in many vertebrates. Is this particularity genetic in origin? Is it acquired in utero, as a function of the position of the foetus? Or during development, under the influence of hormones? All three hypotheses and others are being analysed by the researchers of the EDCBNL project, who are also hoping to find in the study of the foundations of cerebral asymmetry new avenues for understanding schizophrenia, autism and depression.



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