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Abstract:
Recent psycholinguistic research has revealed an
interaction of phonological and prosodic information with
syntactic regularity in sentence processing [e.g., 1]. This
interaction takes on different shapes cross-linguistically,
resulting in a variety of phonological and prosodic "cue
constellations" [2]. A current hypothesis in developmental
psycholinguistics is that these cue constellations contribute
importantly to early acquisition of syntax by "bootstrapping" the
child into the target language. An outstanding question in
this research concerns how these cue constellations emerge, and
what possible shapes they assume. We offer computational
simulations of this emergence that illuminate how phonological
and prosodic information comes to subserve language acquisition,
and efficiently coordinate sentence processing.
A phrase-structure grammar template was used to
generate sentences along with a set of associated cues for the
training of simple recurrent networks (SRNs). The template
incorporated a number of parameters that could be "mutated"
across generations of networks. These parameters included
(1) head ordering of phrase-structure rules (right-headed vs.
left-headed rules); (2) places at which pauses could delimit
structure (sentence vs. noun-phrase pauses); and (3) lexical cues
(units devoted to words in the grammar). For each
generation of networks, the template instantiation for which the
SRNs acquired the most linguistic structure was selected as the
winning grammar, and had some of its parameters mutated.
This process was continued over many generations, allowing the
cue constellations for winning grammars to evolve.
Our results offer clues about the emergence of cue
constellations. First, in all simulations performance
improved across generations. Second, the lexical level cue
fluctuated significantly more in lexically simple languages, and
became consistent with growing complexity (i.e., number of
lexical items in the grammar template). It seems,
therefore, that certain cues are more consistently exploited as
languages become more complex. Third, pauses were
consistently located regardless of lexical complexity (for
example, at syntactic boundaries like noun phrases and verb
phrases). This suggests that cues relevant to syntactic
phrases are important for emerging languages with even
impoverished vocabulary.
In conclusion, we argue that cue constellations
adapt to service growing lexical and syntactic structure.
Fueled by constraints on learning, cues facilitate the
acquisition of complex linguistic structure, and inevitably
contribute to coordinating sentence processing. These
simulations serve as a first step towards understanding the
principles that may underlie the emergence of phonological and
prosodic cues, and how these emerging cue constellations service
language acquisition and adult sentence processing.
References
[1] Kjelgaard, M. & Speer, S.
(1999). Prosodic facilitation and interference in the
resolution of temporary syntactic closure ambiguity.
Journal of Memory and Language, 40, 143-194.
[2] Fisher, C. & Tokura, H.
(1996). Acoustic cues to grammatical structure in
infant-directed speech: Cross-linguistic evidence. Child
Development, 67, 31923218.
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