588 Text Comprehension and Discourse Processing
comprehension—both at the word level as well as at the syn-
tactic and discourse levels—are context independent and
unconstrained. Thus, they are inherently promiscuous. How-
ever, context quickly imposes its constraints. Constructions
that are consistent with each other support each other in a
spreading activation process, and inconsistent and irrelevant
constructions become deactivated. According to this model,
the construction process results in an incoherent mental rep-
resentation. An integration process is needed to turn this
contradictory tangle of hypotheses into a coherent mental
representation. This integration is essentially a process of
constraint satisfaction. It works quickly enough so that inap-
propriate initial hypotheses do not reach the level of con-
sciousness. According to experimental results (e.g., Till,
Mross, & Kintsch, 1988) it takes about 300–350 ms for word
meanings to become fixated in a discourse context, and
500–700 ms for topic inferences.
Schemas play an important role in the construction-
integration model, because they are likely to be activated in
the construction phase of the process, just like many other
knowledge structures. However, once activated, an appropri-
ate schema will most likely become the central unit in the
integration phase, attracting relevant pieces of information
and thereby deactivating schema-irrelevant constructions.
W. Kintsch (1998) describes how this model can account
for a wide variety of experimental findings, such as the
construction of word meanings in discourse, priming in dis-
course, syntactic parsing, macrostructure formation, generat-
ing inferences, and the construction of situation models. The
construction-integration model has also been successfully
applied to how people solve mathematical word problems,
and beyond the sphere of text comprehension, to action plan-
ning, problem solving, and decision making (for more infor-
mation on human performance in these tasks, see the chapter
in this volume by Leighton & Sternberg). In other words, the
model aspires to be a general theory of comprehension, not
just of text comprehension.
The Collaborative Activation-Based Production
System Architecture
The bottom-up, spreading activation component of the
construction-integration model is quite successful and has
been included in most subsequent models of text comprehen-
sion. Models of comprehension can be broadly described as
attempts to instantiate activation-based theories of compre-
hension within limitations suggested by other cognitive
processes. Given the importance of working memory re-
sources for comprehension, it is not surprising that many mod-
els have focused on constraints surrounding comprehension
processes when developing simulations. Just and Carpenter
(1992) developed a model of sentence comprehension that
attempted to account for characteristics of comprehension
based on a flexible but limited capacity system simulating the
constraints of working memory. It should be noted that
although the capacity-constraints of the collaborative action-
based production system (CAPS) are based on working
memory characteristics, they relate to theoretically based,
higher-level activation limits rather than to modality-specific
buffers commonly thought to exist within working memory
(e.g., Baddeley, 1986; also see the chapter in this volume by
Nairne).
The CAPS architecture is a combination of a production
system and an activation-based connection system that Just
and Carpenter (1992) used to produce a simulation of their
theory. According to the theory, activation is responsible both
for storage and processing components of language compre-
hension. In CAPS, an element is activated either by being
constructed from text (written or spoken), constructed by a
process, or retrieved from long-term memory. Like the
construction-integration model, CAPS does not neglect the
influence of top-down effects of context. In fact, CAPS as-
sumes that activation of text propositions and background
knowledge proceeds similarly to the construction-integration
model. However, the difference in CAPS appears when the
comprehension processes approach capacity limits.
Although elements with above-threshold activation are
available to comprehension processes, complications occur
when the amount of activation required for elements exceeds
the total activation available in the system. Capacity limits in
CAPS do not necessarily result in deactivation of weak ele-
ments, but rather in an overall decrease of system activation.
In CAPS, activation for maintaining elements as well as for
processing these elements is shared. Thus, capacity limits on
activation can lead to forgetting of old elements as well as
decreased processing of current elements.
Just and Carpenter’s (1992) model is quite successful at
modeling comprehension differences produced by texts with
differing working memory demands as read by individuals
with varying working memory capacity. Interestingly, Just
and Carpenter (1992) argue that their evidence suggests that
activation capacity is a single resource. They assert that be-
cause increasing demand by a variety of methods—for exam-
ple, increasing text distance or ambiguity, reducing available
working memory capacity—produces consistent effects on
comprehension, it is reasonable to assume that the same
mechanisms underlie diverse types of comprehension pro-
cessing. Clearly, cognitive processes are subject to capacity
limits, and the power of this model lies in the dynamic man-
ner in which it accounts for such limits in comprehension.