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

maintain the items in memory (Baddeley, 1986, 1990; Conrad, 1964a, 1964b; Waugh
& Norman, 1965). As a result, asking subjects to verbalize their thinking steps is
presumed to provide accurate access to current cognitive processing, and to do so
with minimal disruption. “Verbalization will not interfere with ongoing processes
if the information stored in STM is encoded orally, so that an articulatory code can
readily be activated” ” (Ericsson & Simon, 1984, p. 68).
In order to study problem solving, Newell and Simon (1972) collected verbal
protocols for problems that were difficult enough to engage subjects and generate
interesting behaviour, but simple enough to be solved. For instance, when a
subject was asked to decode the cryptarithmetic problem DONALD + GERALD =
ROBERT after being told that D = 5, they solved the problem in twenty minutes and
produced a protocol that was 2,186 words in length.
The next step in the study was to create a problem behaviour graph from a subject’s
protocol. A problem behaviour graph is a network of linked nodes. Each node
represents a state of knowledge. For instance, in the cryptarithmetic problem such
a state might be the observation that “R is odd.” A horizontal link from a node to a
node on its right represents the application of an operation that changed the state
of knowledge. An example operation might be “Find a column that contains a letter
of interest and process that column.” A vertical link from a node to a node below
represents backtracking. In many instances, a subject would reach a dead end in
a line of thought and return to a previous state of knowledge in order to explore a
different approach. The 2,186-word protocol produced a problem behaviour graph
that consisted of 238 different nodes.
The initial node in a problem behaviour graph represents a subject’s starting
state of knowledge when given a problem. A node near the end of the problem behaviour
graph represents the state of knowledge when a solution has been achieved.
All of the other nodes represent intermediate states of knowledge. Furthermore,
in Newell and Simon’s (1972) research, these intermediate states represent very
detailed elements of knowledge about the problem as it is being solved.
The goal of the simulation component of Newell and Simon’s (1972) research
was to create a computer model that would generate its own problem behaviour
graph. The model was intended to produce a very detailed mimicry of the subject’s
behaviour—it was validated by examining the degree to which the simulation’s
problem behaviour graph matched the graph created for the subject. The meticulous
nature of such intermediate state evidence provided additional confidence for
the use of verbal protocols as scientific data. “For the more information conveyed in
their responses, the more difficult it becomes to construct a model that will produce
precisely those responses adventitiously—hence the more confidence we can place
in a model that does predict them” (Ericsson & Simon, 1984, p. 7).
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