Thursday, December 22, 2005

Psychological debate. Neuroscience to the rescue!

Some weeks ago I mentioned the lack of interest in the brain as a serious problem for Evolutionary Psychology. Now, this resistance to neuroscience may be a general misère within psychology – already back in the 1980’s Martha Farah attacked psychologists for fighting over mental imagery without introducing any neurobiological evidence into the debate. Perhaps psychologists are still functionalists at heart, feeling that neuroscience have no bearing on psychological models. However, when you argue that a psychological function is an evolutionary adaptation, as evolutionary psychology do, it becomes rather problematic to leave out the brain part from your equation, since evolution doesn’t actually operate on functions, but on the genome. And the genome, again, doesn’t build functions but proteins which, in the end, build brains and (again again) not functions, by forming molecules. So, if you are interested in psychological functions as evolutionary adaptations, you simply have to through brain processes.

Luckily, some evolutionary psychologists are starting to do exactly that. In the recent December issue of NeuroImage, Laurence Fiddick presents the results of an fMRI study investigating the question if some deontic conditional rules are easier to reason about, since they are “social” in nature, relative to other “non-social” deontic rules of a similar logical form. Leda Cosmides, back in the 1980’s, proposed that social situations are computed by certain, special social cognitive modules, not by a general-purpose, logical reasoning machine. She went on to investigate this hypothesis using Wason’s selection task, albeit only collecting behavioural data. Over the years, several authors have criticised Cosmides’s data for not really demonstrating a content effect, generating a somewhat heated discussion on the topic (see especially David Buller’s book Adapting Minds, MIT 2005). Yet, until Fiddick’s experiment, nobody had tried to see if Cosmides’s putative “social” deontic rules actually activate a particular set of neural structures in contrast to other forms of deontic rules. Here are the results, quoting from the abstract of Fiddick's paper:

Although the rules and the demands of the task were matched in terms of their logical structure, reasoning about social contracts and precautions activated a different constellation of neurological structures. The regions differentially activated by social contracts included dorsomedial PFC (BA 6/8), bilateral ventrolateral PFC (BA 47), the left angular gyrus (BA 39), and left orbitofrontal cortex (BA 10). The regions differentially activated by precautions included bilateral insula, the left lentiform nucleus, posterior cingulate (BA 29/31), anterior cingulate (BA 24) and right postcentral gyrus (BA 3). Collectively, reasoning about prescriptive rules activated the dorsomedial PFC (BA 6/8).

Does these diffuse networks constitute on the one hand a social module and on the other a logical “precaution” module? Hardly. But, as Fiddick (prudently) state, his results do “reinforce the view that human reasoning is not a unified phenomenon, but is content-sensitive.” Human reasoning is thus content-sensitive, but not modular. This is surely progress. Thanks neuroscience!

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