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Ch 5. Language Change: A Preliminary Model 5.1 ~ 5.2 The Computational Nature of Language Learning and Evolution P. Niyogi 2006 Summarized by Kwonill, Kim Biointelligence Laboratory, Seoul National University http://bi.snu.ac.kr/ 2009.07.30
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Contents 5.0 Language Acquisition vs. Language Change Slightly imperfect individual learning Language change in the population level Learning vs. Evolutionary dynamics 5.1 An Acquisition-Based Model of Language Change Qualitative explanation 5.2 A Preliminary Model 5.2.1 Learning by Individuals 5.2.2 Population Dynamics 5.2.3 Some Examples Memoryless Learners Batch Error-Based Learner Cue-Based Learner 5.3 Implications and Further Directions 2(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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Language Acquisition vs. Language Change Language Acquisition The mechanism by which language is transmitted from parrent to child Perfect acquisition = Perfect transmission Perfectly same language = No change! However, a number of language-change cases are reported. Imperfect learning! 3(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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Is it Possible Language Change by Slightly imperfect learning ? It is possible Slightly imperfect individual learning Language change in the population level Lightfoot (1991) Someone’s new parameter setting New grammar Different output Linguistic environmental change New parameter setting in younger people New grammar … Let’s show formally Relations between Learning & Evolutionary dynamics A model of language change emerges as a logical consequence of language acquisition 4(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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An Acquisition-Based Model of Language Change (1/3) We want … Grammatical theory + Learning algorithm Model of language change Individual level problem Population level problem Learning problem (Individual level) PLD(Primary Linguistic Data) “How children acquire the target language from their PLD?” Linguistic composition change problem (Population level) Changeable Case 1: PLD for children is altered By foreign speakers, disfluencies, … Changeable Case 2: Finite sentences from grammar 5(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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An Acquisition-Based Model of Language Change (2/3) Finite sentences from the adults’ grammar Slightly different grammar of children Over successive generations, the linguistic composition evolves as a dynamical system Microscopic & macroscopic view Different learning models Different evolutionary results 6(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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An Acquisition-Based Model of Language Change (3/3) Assumptions Grammar hypothesis space The space of possible grammars that humans might acquire Usually simplified to particular parameters Language acquisition device The learning algorithm the child uses to develop grammatical hypotheses on the basis of data Primary linguistic data (PLD) The distribution of sentences that a child is exposed to and that affect its linguistic development 7(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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A Primary Model Σ: a finite alphabet Σ*: all possible series of character Language: L i ⊂ Σ* In general, L 1 ∩ L 2 ≠ g i means the grammar of the language L i 8(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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A Primary Model Consider ONLY TWO languages, L 1 & L 2 Monolingual case: just ONE language for ONE user Population: TWO generations State variable α t : proportion of users of L 1 at the t th generation 1- α t : `` `` L 2 `` Sentence : s ∈ Σ* P 1 : Probability distribution of sentences of L 1 P 1 (s) : Probability to produce a sentence s by a user of L 1 9(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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Learning by Individuals : learning algorithm 10(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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Population Dynamics Finite sentences for learning “Mature” after K examples Begin All uses L 1 All example are s ~ P 1 11(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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Summary Phase Space Linear Stability Analysis Nullclines Poincare-Bendixson Theorem Hopf Bifurcation Population Dynamics in the Wilson-Cowan Model 12(C) 2009, SNU Biointelligence Lab, http://bi.snu.ac.kr/http://bi.snu.ac.kr/
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