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Abstract:
Our use of language depends upon a mental lexicon of
memorized words, and a mental grammar of rules, including
operations and constraints, which underlie the sequential and
hierarchical composition of lexical forms into predictably
structured larger words, phrases, and sentences.
The Declarative/Procedural model posits that the lexicon/grammar
distinction in language is tied to the distinction between two
fundamental brain memory systems, each underlying particular
non-language functions (1). On this view, the memorization and use
of words - at least those with non-compositional (arbitrary)
sound-meaning pairings - depends upon an associative memory of
distributed representations that is subserved by temporal-lobe
circuits previously implicated in the learning and use of fact and
event knowledge. This system appears to be specialized for learning
arbitrarily-related information (i.e., for associative binding). In
contrast, the acquisition and use of grammatical rules that
underlie the symbolic manipulation of linguistic forms is subserved
by frontal/basal-ganglia circuits previously implicated in the
implicit (non-conscious) learning and expression of motor and
cognitive "skills" and "habits" (e.g., from simple motor acts to
skilled game playing). This system may be specialized for
sequences, and appears to be largely informationally encapsulated
(see 2, 3).
This novel view of lexicon and grammar offers an alternative to
the two main competing theoretical frameworks. Although it shares
the perspective of traditional Dual-System theories in positing
that the mental lexicon and a symbol-manipulating mental grammar
may be subserved by distinct posterior and anterior brain regions,
respectively, it diverges from these theories where they assume
components dedicated (domain-specific) to each of the two language
capacities, and in their assumption that lexical memory is a rote
list of items (see 4, 5, 6). Conversely, while it shares with
Single-System theories the perspective that the two capacities are
subserved by domain-general circuitry, it diverges from them where
they link both capacities to a single associative memory system
with broad anatomic distribution (see 7, 8, 9).
The Declarative/Procedural model, but neither traditional
Dual-System nor Single-System models, predicts double dissociations
between lexicon and grammar, with associations among associative
memory properties, memorized words and facts, and temporal-lobe
structures, and among symbol-manipulation properties, grammatical
rule-products, motor skills, and frontal/basal-ganglia
structures.
In order to contrast lexicon and grammar while holding other
factors constant, my colleagues and I have focused our studies on
morphologically complex word forms. We have contrasted
morphophonological transformations that are (largely) unproductive
(e.g., in go-went, solemn-solemnity), and which therefore must
depend upon memory, with those that are fully productive (e.g., in
walk-walked, happy-happiness), and which therefore may be computed
by grammatical rules.
Evidence will be presented from morphological contrasts in
several languages, including English, German, Italian, and
Japanese, from studies that use a range of psycholinguistic and
neurolinguistic approaches with children and adults: the
examination of frequency, neighborhood, and priming effects; the
behavioral testing of patients with developmental, acquired, and
neurodegenerative disorders, including Specific Language
Impairment, Williams syndrome, aphasia, and Alzheimer's,
Parkinson's, and Huntington's diseases; and neuroimaging, using
fMRI, EEG/ERPs, and MEG. It will be argued that converging evidence
from these studies supports the Declarative/Procedural model of
lexicon and grammar.
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