Mind, Body, World- Foundations of Cognitive Science, 2013a

the electronic circuits which performed the basic arithmetic operations [in ENIAC]
were simply electronic analogs of the same units used in mechanical calculators and
the commercial accounting machines of the day” (Williams, 1997, p. 272).
The realization that cognitive systems must be examined from multiple levels
of analysis motivated Marr’s (1982) tri-level hypothesis. According to this hypothesis,
cognitive systems must be explained at three different levels of analysis: physical,
algorithmic, and computational.
It is not enough to be able to predict locally the responses of single cells, nor is it
enough to be able to predict locally the results of psychophysical experiments. Nor
is it enough to be able to write computer programs that perform approximately in
the desired way. One has to do all these things at once and also be very aware of the
additional level of explanation that I have called the level of computational theory.
(Marr, 1982, pp. 329–330)
The tri-level hypothesis provides a foundation for cognitive science and accounts
for its interdisciplinary nature (Dawson, 1998). This is because each level of analysis
uses a qualitatively different vocabulary to ask questions about cognitive systems
and uses very different methods to provide the answers to these questions. That is,
each level of analysis appeals to the different languages and techniques of distinct
scientific disciplines. The need to explain cognitive systems at different levels of
analysis forces cognitive scientists to be interdisciplinary.
Marr’s (1982) tri-level hypothesis can also be used to compare the different
approaches to cognitive science. Is the tri-level hypothesis equally applicable to the
three different schools of thought? Provided that the three levels are interpreted
at a moderately coarse level, it would appear that this question could be answered
affirmatively.
At Marr’s (1982) implementational level, cognitive scientists ask how information
processes are physically realized. For a cognitive science of biological agents,
answers to implementational-level questions are phrased in a vocabulary that
describes biological mechanisms. It would appear that all three approaches to cognitive
science are materialist and as a result are interested in conducting implementational-level
analyses. Differences between the three schools of thought at this level
might only be reflected in the scope of biological mechanisms that are of interest.
In particular, classical and connectionist cognitive scientists will emphasize neural
mechanisms, while embodied cognitive scientists are likely to be interested not only
in the brain but also in other parts of the body that interact with the external world.
At Marr’s (1982) algorithmic level, cognitive scientists are interested in specifying
the procedures that are used to solve particular information processing
problems. At this level, there are substantial technical differences amongst the
three schools of thought. For example, classical and connectionist cognitive scientists
would appeal to very different kinds of representations in their algorithmic
Marks of the Classical? 349