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contexts. But while it is true that we have gotten better about acknowledging the
limitations of our instinctive reductionism - a bit of humility that the media would
do well to absorb into its reporting - actual scientific practice has yet to be much
affected by awareness of those limits. A recent case in point is John Anderson's
project to map ACT-R components to brain regions [3]. The motivations for the
project are of course entirely sound: if ACT-R is to be a realistic model of human
cognition, then that model ought to have some significant, testable relationship to
the neural bases of cognition. In this particular set of experiments, the authors iden-
tify eight ACT-R modules and match each one to a different region of interest. They
then look for, and find, significant fit between the predictions for the BOLD signal in
those regions, based on the activity of the ACT-R modules while solving a particular
arithmetic task, and the measured BOLD signal in human participants performing
the same task. On its face, this is an intriguing result and seems to offer compelling
support for the ACT-R model. But the methodological assumption of the project -
that there is a 1:1 mapping of ACT-R modules and brain areas - is highly suspect.
Nor are the authors unaware of this difficulty, and in fact they specifically caution
against making any inference from their approach to the functional organization of
the brain:
Some qualifications need to be made to make it clear that we are not propos-
ing a one-to-one mapping between these eight regions and the eight functions.
First, other regions also serve these functions. Many areas are involved in vi-
sion and the fusiform gyrus has just proven to be the most useful to monitor.
Similarly, many regions have been shown to be involved in retrieval, particu-
larly the hippocampus. The prefrontal region is just the easiest to identify and
seems to afford the best signal-to-noise ratio. Equally, we are not claiming
these regions only serve one function. This paper has found some evidence for
multiple functions. For instance, the motor regions are involved in rehearsal
as well as external action (213-4).
Although we should appreciate the authors' candor here, the caveat seriously
undermines the ability to interpret their results. If from the discovery that activity
in an ACT-R module predicts the BOLD signal in specific brain region, we can
neither infer that the region serves that specific function (because it is also activated
in other tasks), nor that the function is served by that region (because other regions
are activated by the target task), then we are not left with much. And yet despite
the authors' awareness of these problems, they stick by the methodology that causes
them.
Why might this be so? Naturally, all scientists are faced with the necessity of
making simplifying abstractions to increase the tractability of their work; but as the
authors found themselves, the assumption of a 1:1 mapping of modules to brain
areas is not an approximation to reality, but appears to be fundamentally mislead-
ing. So what would account for the fact that they persist in applying methodological
assumptions that they know to be inadequate? Given the scientific stature of the
