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- Date de réalisation : 22 Juin 2012
- Durée du programme : 20 min
- Classification Dewey : Psycholinguistique, Troubles de la parole et du langage (troubles de la communication, de l'articulation ; orthophonie)
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- Catégorie : Conférences
- Niveau : niveau Master (LMD), niveau Doctorat (LMD), Recherche, L3
- Disciplines : Disciplines connexes (sociolinguistique, psycholinguistique…), Psychologie cognitive
- Collections : Perspectives neuropsycholinguistiques sur l'aphasie
- ficheLom : Voir la fiche LOM
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- Auteur(s) : VAN EGMOND Marjolein
- producteur : Université Toulouse II-Le Mirail
- Réalisateur(s) : BASTARD Bruno
- Editeur : SCPAM Université Toulouse II-Le Mirail
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- Langue : Anglais
- Mots-clés : troubles de la parole, aphasie, langage gestuel
- Conditions d’utilisation / Copyright : Tous droits réservés à l'Université Toulouse II-Le Mirail et aux auteurs.
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Zipf's law in aphasia / Marjolein Van Egmond
Zipf's law in aphasia / Marjolein Van Egmond. In "Perspectives neuropsycholinguistiques sur l'aphasie - NeuroPsychoLinguistic Perspectives on Aphasia", colloque international organisé par l'Unité de Recherche Interdisciplinaire Octogone de l'Université Toulouse II-Le Mirail (France). Toulouse, 21-23 juin 2012.
In
spontaneous speech, quantitative measures can provide valuable
insight into general properties of words while generalizing over the
content of the conversation. This renders it a suitable method to
investigate word finding difficulties in aphasia. The quantitative
measure employed in the current project is the distribution of word
frequencies. Word frequencies in natural language texts typically
conform to Zipf’s law, a power law P(k)~k α,
where p(k)
is the frequency of the kth
word if words are ordered by decreasing frequency. This law can also
be formulated as pƒ~ƒ β,
where pƒ
is the proportion of words whose frequency is ƒ in a given sample
text. Typically, it is found that α≈1
and β≈2.
The
meaningfulness of Zipf’s law has been a topic of heated discussion.
Zipf (1949) claimed that this word frequency distribution was due to
the principle of least effort. But his opponents claimed that the
statistics of simple random sequences of characters reproduce Zipf’s
law equally well (e.g. Li, 1992; Miller & Chomsky, 1963).
However, in both cases comparison between groups can reveal important
differences between them.
Zipf’s
law has been shown to apply to every natural language text in every
language for which it has been tested (Baroni, 2008). The first to
test Zipf’s law in aphasia were Howes and Geschwind (1964). They
found that aphasic speech still conforms to Zipf’s law, but with a
different slope. However, besides methodological issues, it is
unclear where this difference arises: in function words only – for
which problems in aphasic speech are well-known – or also in
content words. This, therefore, was the goal of the present study, in
which speech from people with non-fluent aphasia was analyzed.
Spontaneous
speech of four Dutch non-fluent aphasic speakers was recorded and
analyzed, and compared to speech of four healthy speakers from the
Corpus of Spoken Dutch. Three analyses were made: one with full
samples, one with only content words and one with only function
words. Both α
and β
were measured.
For
the α-analysis,
it was found that Zipf’s law applies in all analyses. α
was
found to be significantly higher for aphasic speakers compared to
healthy speakers. For β,
Zipf’s law applies to all analyses for healthy speakers, but only
to content words in people with aphasia; for function words it was
found that Zipf’s law does not apply. In the content words
analysis, β
was
significantly lower for aphasic speakers compared to healthy
speakers. Interestingly, in the all-words analysis in healthy adults
both α
and β
were found to be lower than the typically reported values.
We
argue that β
is more sensitive than α
for mathematical reasons. We argue that our findings indicate that
the mental lexicon of non-fluent patients is not qualitatively
different from that of unimpaired populations. The deficit is due to
reduced processing capacities in these patients, which affects
lexical retrieval. The retrieval of function words is affected most.
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