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

One might think that artifacts are not important because they are not explicit
consequences of a design. However, in many cases artifacts are crucial sources of
information that help us reverse engineer an information processor that is a “black
box” because its internal mechanisms are hidden from view.
2.9 Algorithms from Artifacts
Neuroscientist Valentino Braitenberg imagined a world comprising domains of
both water and land (Braitenberg, 1984). In either of these domains one would find
a variety of agents who sense properties of their world, and who use this information
to guide their movements through it. Braitenberg called these agents “vehicles.”
In Braitenberg’s world of vehicles, scientists encounter these agents and attempt to
explain the internal mechanisms that are responsible for their diverse movements.
Many of these scientists adopt what Braitenberg called an analytic perspective: they
infer internal mechanisms by observing how external behaviours are altered as a
function of specific changes in a vehicle’s environment. What Braitenberg called
analysis is also called reverse engineering.
We saw earlier that a Turing machine generates observable behaviour as it calculates
the answer to a question. A description of a Turing machine’s behaviours—
be they by design or by artifact—would provide the sequence of operations that
were performed to convert an input question into an output answer. Any sequence
of steps which, when carried out, accomplishes a desired result is called an algorithm
(Berlinski, 2000). The goal, then, of reverse engineering a Turing machine or
any other calculating device would be to determine the algorithm it was using to
transform its input into a desired output.
Calculating devices exhibit two properties that make their reverse engineering
difficult. First, they are often what are called black boxes. This means that we can
observe external behaviour, but we are unable to directly observe internal properties.
For instance, if a Turing machine was a black box, then we could observe its
movements along, and changing of symbols on, the tape, but we could not observe
the machine state of the machine head.
Second, and particularly if we are faced with a black box, another property that
makes reverse engineering challenging is that there is a many-to-one relationship
between algorithm and mapping. This means that, in practice, a single input-output
mapping can be established by one of several different algorithms. For example,
there are so many different methods for sorting a set of items that hundreds of
pages are required to describe the available algorithms (Knuth, 1997). In principle,
an infinite number of different algorithms exist for computing a single input-output
mapping of interest (Johnson-Laird, 1983).
Multiple Levels of Investigation 43