Stanislas Dehaene is a mathematician and neuropsychologist who has written two popular books, The Number sense: How the Mind Creates Mathematics and Reading in the Brain. Using fMRI and magneto-encephalography (MEG), Dehaene and his colleagues have made much progress in relating cognitive function and brain function. The two books are quite readable even though much of the material is likely to be brand new to the reader.
In Reading in the Brain, Dehaene introduces the idea of “neuronal recycling” whereby portions of our ventral visual system is turned over to reading and writing. He says that after centuries of trial and error, writing systems evolved to a form adapted to our brain circuits. He points out that human cultures are not areas of infinite diversity because the human capacity for invention is narrowed by our limited neuronal construction set. Cultural forms and writing systems seem diverse, but there are limits. All writing systems represent word roots, phonological structures, and a small inventory of visual shapes.
Dehaene believes that two things make possible the uniqueness of human culture. The first thing is what is called the “theory of the mind”–the mental representation of the intentions and beliefs of others. The second is what Dehaene calls the global neuronal workspace. This provides the capacity to arrive at new combinations of ideas and conscious mental synthesis. Dehaene suggests that the human brain’s tremendous fiber bundles under the frontal lobes compared to other primates allow massive increases of connectivity and that it serves to convey input from several brain areas to the global neuronal workspace. This workspace assembles, confronts, recombines, and synthesizes knowledge. Dehaene says that the prefrontal cortex with its connections to all the high-level areas, provides a space for deliberation fed by a whole set of perceptions and memories. Prefrontal neurons are multimodal and they can fire for several dozen seconds and keep the working memory for as long as needed.
Dehaene sees that the evolution of the global workspace allows it to exploit the cultural cognitive niche made possible by neuronal recycling. The prefrontal cortex, according to Dehaene, functions like a primitive “Turing machine.” It operates slowly and makes mistakes, but it can be creative. Reading is the finest result so far.
Most of his work has not been directly related directly to judgment and decision making. I am going to discuss the most salient points of a paper published in November 2011 in PLos Biology, “How Awareness Changes the Relative Weights of Evidence During Human Decision-Making.” The main author of this paper is Floris P. de Lange along with Simon van Gaal, Victor Lamme, and Dehaene. In the study, participants had to indicate the prevailing direction of five arrows presented on a screen over a few hundred milliseconds that each pointed either left or right, and in different trials these arrows were either easy to see or difficult to see. The behavioral and neural recordings indicated that the impact of later evidence was reduced when more evidence had been accrued but only for highly visible information. For difficult to perceive information, the information contributed equally to the decision. The authors suggest that consciousness may play a role in decision making by biasing the accumulation of new evidence.
Another Dehaene article from 2012, “From a single decision to a multi-step algorithm,”continues on the Turing machine idea. Alan Turing helped to break the German enigma code and formalized a sequential computing device, the Turing machine. Although the computer has been seen as the wrong metaphor for the cognition of the human brain, Dehaene suggests that the Turing view of serial computations may be comparable to the role of a central executive system in serial decision making and conscious thought. An example of this would be calculating 23 x 74 in your head. This competence involves serial chains of successive decisions each based on an accumulation of evidence up to a threshold and forwarding the result.
Dehaene argues that the configuration of the decision making process requires a distinctive control mechanism that provides flexibility at the price of slow serial speed. He sees the framework as having two elements:
- A vast parallel machinery for decision making for accumulation of multiple sources of evidence, which contributes to intuition and moves us to action.
- A capacity to link decisions into tactics where the outputs of one decision become the inputs of the next. This capacity acts as a central executive that routs information, task setting, and task sequencing.
The figure below from the article provides an illustration of the framework.
Dehaene, S. (2009) Reading in the Brain. New York: Viking.
Dehaene, S. (1997). The Number Sense: How the Mind Creates Mathematics. New York: Oxford University Press.
Deheaene, S. (2012). From a single decision to a multi-step algorithm. Current Opinion in Neurobiology, 22: 1-9.
de Lange, F., van Gaal, S., Lamme, V., & Dehaene, S.(2011). How Awareness Changes the Relative Weights of Evidence During Human Decision-Making. PLoS Biology, November 2011, Vol 9, Issue 11.