Page 62 - Deep Learning

The Nature of the Enterprise 45

that such-and-such a learning mechanism was operating on such-and-such an
occasion is an ad hoc reconstruction instead of an explanatory account.

Patterns as Explanatory Targets
Sometimes the target for a cognitive explanation is a single learning event, a
change in knowledge that a person underwent on a particular occasion. For
example, we might want to explain why a student failed to learn a piece of sub-
ject matter in a given learning scenario. This type of detailed analysis of single
events has precedents in other sciences: Evolutionary biologists might attempt
to explain the evolution of a particular species, while economic analysts might
try to explain the rise and fall of a particular company. 49
However, the more significant explanatory targets are patterns of change.
A pattern is not a theory or an explanation, but a description of the general
character of the change a system undergoes over time. To take an example
from paleontology, the temporal pattern in the fossil record is one of relatively
short periods of speciation followed by much longer periods of stasis during
which a species does not change, which in turn are followed by relatively short
periods of decline, ending in extinction; this pattern is known as punctuated
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equilibrium. In economics, another well-known pattern is the existence of
business cycles, the regular succession of booms and busts in the market. In the
Earth sciences, the pattern of advance and retreat of the world’s glaciers is a
major explanatory target. In human cognition, the best-documented pattern
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of change is the learning curve: If the time to complete a practice problem is
plotted as a function of how many practice problems the person has solved
already, the result is a smoothly decelerating curve.
Patterns are important in part because they are more difficult to explain
than individual learning events. Any single learning event can be explained if
we are free to include any representation and any repertoire of basic processes
among our premises. But an explanation for a pattern must show not only how
the change can come about but also why it recurs. If geologists had found only
a single meandering river on the entire planet, they could have attributed it to
unique local conditions, but because rivers meander all over the Earth, the expla-
nation for meandering draws upon recurring factors such as silt deposit and bank
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erosion. Patterns are powerful clues to the mechanisms that produce them.
Patterns of change often unfold over a period of time that is significantly
longer than the duration of a single unit change. A pattern is a cumulative
outcome of multiple applications of the basic change mechanisms. A focus on
patterns forces the theorist to consider how the effects of the basic mechanisms