Connectionist Modeling of Experience-based Effects in Sentence ...

1.3 Psycholinguistic Aspects
verb counts as a new discourse referent. Establishing the relation between the relative
pronoun who and the empty element consumes 2 EU because two discourse referents
(senator and attacked) have been processed meanwhile. The biggest cost is assigned to
the main verb (admitted). Here the subject reporter is integrated after processing three
new discourse referents (the embedded subject, the embedded verb, and the main verb).
Additionally an NP head is predicted because the verb is transitive. The last integration
takes place at the last word error. The integration of the determiner produces no
cost, whereas building the structural relation with its head admitted consumes 1 EU.
Altogether the total cost predicts the highest difficulty at the main verb, resulting from
the long distance from its dependent arguments. Using the total cost as a reading time
predictor the DLT perfectly predicts locality effects.
CC-READER
A computational model in its basic assumptions consistent with the DLT cost association
is the Capacity Constrained READER or CC-READER (Just and Carpenter, 1992;
2002), the successor of READER, a sentence reading model implemented in a framework
called CAPS (Collaborative Activation-based Production System). CC-READER
is an activation-based simulation of linguistic working memory processes with a limited
capacity as explanatory factor for memory load effects and individual differences. The
constituting mechanism of CAPS is activation propagation caused by symbolic production
rules. Both productions and stored elements (words, structures, propositions, etc.)
use the same resources. The availability of elements as well as the applicability of productions
is dependent on their received activation exceeding a certain threshold. The
condition for a production rule is met when the activation threshold of the respective
source element is reached. An important architectural property of CC-READER is the
usage of processing cyles. In each processing cycle all currently applicable production
rules fire simultaneously, meaning they propagate weighted activation from the source to
a “target element”. In this sense capacity is defined by the maximally available amount
of activation that can be used by all productions and stored elements per processing
cycle. In case of activation shortage thresholds can be reached by incremental production
firing, resulting in more processing cycles. This is what happens when the total
activation has to be “scaled back” because it exceeds the capacity limit. A back-scaling
affects the activation of both productions and stored items: “Any shortfall of activation
is assessed against both storage and processing, in proportion to the amount of
activation they are currently consuming” (Just and Carpenter, 1992; p. 135). Reading
word-by-word, the parsing process also depends on lexical access and constructs a
representation of the sentence that includes thematic role information. Slow-downs in
processing are represented by an increased number of processing cycles. The two concepts
of activation propagation and processing cycles enable CC-READER to predict a)
reading slow-downs in demanding sentence regions (due to storage of many elements or
firing of many productions) and b) region-specific individual differences in reading; both
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