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

2.10 Architectures against Homunculi
We have described an algorithm for calculating an input-output mapping as a
sequence of operations or behaviours. This description is misleading, though,
because the notion of sequence gives the impression of a linear ordering of steps.
However, we would not expect most algorithms to be linearly organized. For instance,
connectionist cognitive scientists would argue that more than one step in an algorithm
can be carried out at the same time (Feldman & Ballard, 1982). As well, most
algorithms of interest to classical cognitive scientists would likely exhibit a markedly
hierarchical organization (Miller, Galanter, & Pribram, 1960; Simon, 1969). In
this section, I use the notion of hierarchical organization to motivate the need for an
algorithm to be supported by an architecture.
What does it mean for an algorithm to be hierarchical in nature? To answer
this question, let us again consider the situation in which behavioural measurements
are being used to reverse engineer a calculating black box. Initial experiments
could suggest that an input-output mapping is accomplished by an algorithm
that involves three steps (Step 1 Step 2 Step 3). However, later studies
could also indicate that each of these steps might themselves be accomplished by
sub-algorithms.
For instance, it might be found that Step 1 is accomplished by its own fourstep
sub-algorithm (Step a Step b Step c Step d). Even later it could be
discovered that one of these sub-algorithms is itself the product of another sub-subalgorithm.
Such hierarchical organization is common practice in the development
of algorithms for digital computers, where most programs are organized systems of
functions, subfunctions, and sub-subfunctions. It is also a common characteristic of
cognitive theories (Cummins, 1983).
The hierarchical organization of algorithms can pose a problem, though, if an
algorithmic account is designed to explain a calculating device. Consider our example
where Step 1 of the black box’s algorithm is explained by being hierarchically
decomposed into the sub-algorithm “Step a Step b Step c Step d.” On closer
examination, it seems that nothing has really been explained at all. Instead, we have
replaced Step 1 with a sequence of four new steps, each of which requires further
explanation. If each of these further explanations is of the same type as the one to
account for Step 1, then this will in turn produce even more steps requiring explanation.
There seems to be no end to this infinite proliferation of algorithmic steps that
are appearing in our account of the calculating device.
This situation is known as Ryle’s regress. The philosopher Gilbert Ryle raised it
as a problem with the use of mentalistic terms in explanations of intelligence:
Must we then say that for the hero’s reflections how to act to be intelligent he must
first reflect how best to reflect to act? The endlessness of this implied regress shows
46 Chapter 2