Consciousness Blog 13 April 2013

Categorization lies at the base of cognitive activity, yet the neural processes that allow the autonomous construction of categories (as distinct from the import of existing categories through language) are poorly understood. Researchers at Princeton University have used functional magnetic resonance imaging to study the behaviour of the brain while categories came into existence based on their temporal relationships.

As reported in the journal Nature Neuroscience, the researchers presented human participants with sequences of abstract symbols and patterns, which were taken from three sets ("communities") of similar shapes. The presentation process was organized so that similar shapes tended to occur near one another, unknown to the participants. The presentations continued for 30 minutes, after which the participants were asked to break the sequences into what seemed to them appropriate segments. The results corresponded well to the categories which had been set up by the researchers.

Images in the same community produced similar activity in neuron groups at the border of the brain's frontal and temporal lobes. The researchers say that this represents the neural process of associating the images with one another. Different neuronal groups were activated when a symbol from a different community appeared.

Lead author Anna Schapiro, a doctoral student in Princeton's Department of Psychology, says: "We're providing an account of how you come to treat a sequence of experiences as a coherent, meaningful event. "Events are like object categories. We associate robins and canaries because they share many attributes: They can fly, have feathers, and so on. These associations help us build a 'bird' category in our minds. Events are the same, except the attributes that help us form associations are temporal relationships."

Based on the results, the group constructed a computational neural-network model that could predict actual neural events. The principle of "shared temporal context," says Shapiro, underlay the process of establishing the categories. "You have to have experience with the shared temporal structure of the components of the events in order for the event to hold together in your mind," she said. "And the way the brain implements this is to learn to use overlapping neural populations to represent components of the same event."

Michael Frank, a Brown University associate professor of cognitive, linguistic and psychological sciences, said: "The same types of models have been applied to understanding language – for example, how the meaning of words in a sentence can be contextualized by earlier words or concepts. Thus the model and experiments identify a common and previously unappreciated mechanism that can be applied to both language and event parsing, which are otherwise seemingly unrelated domains."

Well, that's correct, but of course it's the other way around: categorization as a principle of cognitive organization and development originated long before humans and language came into existence, at latest with the emergence of the Sauropsids (sharks), and, as always with evolution, a successful, established mechanism is re-used for later instances of the same principle.

Read more in Chapter Two of Agent Human by Michael Bell, The Evolution of Social Consciousness in Animals.


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