In this thesis we use the method of Semantic Mirrors to create a graph of words that are semantically related to a seed word. Spectral graph partitioning methods are then used to partition the graph into subgraphs, and thus dividing the words into different word senses. These methods are applied to a bilingual lexicon of English and Swedish adjectives. A panel of human evaluators have looked at a few examples, and evaluated consistency within the derived senses and synonymy with the seed word.

O fenômeno da ambiguidade lexical foi o tópico central desta pesquisa, especialmente no que diz respeito às relações entre acepções de formas gráficas ambíguas e aos padrões de distribuição de acepções de palavras polissêmicas na língua, isto é, de palavras cujas acepções são semanticamente relacionadas. Este trabalho situa-se como uma proposta de interface entre explorações computacionais da ambiguidade lexical, especificamente de processamento de linguagem natural, e investigações de cunho teórico sobre o fenômeno do significado lexical. Partimos das noções de polissemia e de homonímia como correspondentes, respectivamente, ao caso de uma palavra com múltiplas acepções relacionadas e ao de duas (ou mais) palavras cujas formas gráficas coincidem, mas que apresentam acepções não relacionadas sincronicamente. Como objetivo último deste estudo, pretendia-se confirmar se as palavras mais polissêmicas teriam acepções menos uniformemente distribuídas no corpus, apresentando acepções predominantes, que ocorreriam com maior frequência. Para analisar esses aspectos, implementamos um algoritmo de desambiguação lexical, uma versão adaptada do algoritmo de Lesk (Lesk, 1986; Jurafsky & Martin, 2000), escolhido com base nos recursos linguísticos disponíveis para o português. Tendo como hipótese a noção de que palavras mais frequentes na língua tenderiam a ser mais polissêmicas, selecionamos do corpus (Mac-Morpho) aquelas com maiores ocorrências. Considerando-se o interesse em palavras de conteúdo e em casos de ambiguidade mais estritamente em nível semântico, optamos por realizar os testes apresentados neste trabalho apenas para substantivos. Os resultados obtidos com o algoritmo de desambiguação que implementamos superaram o método baseline baseado na heurística da acepção mais frequente: obtivemos 63% de acertos contra 50% do baseline para o total dos dados desambiguados. Esses resultados foram obtidos através do procedimento de desambiguação de pseudo-palavras (formadas ao acaso), utilizado em casos em que não se tem à disposição corpora semanticamente anotados. No entanto, em razão da dependência de inventários fixos de acepções oriundos de dicionários, pesquisamos maneiras alternativas de categorizar as acepções de uma palavra. Tomando como base o trabalho de Sproat & VanSanten (2001), implementamos um método que permite atribuir valores numéricos que atestam o quanto uma palavra se afastou da monossemia dentro de um determinado corpus. Essa medida, cunhada pelos autores do trabalho original como índice de polissemia, baseia-se no agrupamento de palavras co-ocorrentes à palavra-alvo da desambiguação de acordo com suas similaridades contextuais. Propusemos, neste trabalho, o uso de uma segunda medida, mencionada pelos autores apenas como um exemplo das aplicações potenciais do método a serem exploradas: a clusterização de co-ocorrentes com base em similaridades de contextos de uso. Essa segunda medida é obtida de forma que se possa verificar a proximidade entre acepções e a quantidade de acepções que uma palavra exibe no corpus. Alguns aspectos apontados nos resultados indicam o potencial do método de clusterização: os agrupamentos de co-ocorrentes obtidos são ponderados, ressaltando os grupos mais proeminentes de vizinhos da palavra-alvo; o fato de que os agrupamentos aproximam-se uns dos outros por medidas de similaridade contextual, o que pode servir para distinguir tendências homonímicas ou polissêmicas. Como exemplo, temos os clusters obtidos para a palavra produção: um relativo à ideia de produção literária e outro relativo à de produção agrícola. Esses dois clusters apresentaram distanciamento considerável, situando-se na faixa do que seria considerado um caso de polissemia, e apresentaram ambos pesos significativos, isto é, foram compostos por palavras mais relevantes. Identificamos três fatores principais que limitaram as análises a partir dos dados obtidos: o viés político-jornalístico do corpus que utilizamos (Mac-Morpho) e a necessidade de serem feitos mais testes variando os parâmetros de seleção de coocorrentes, uma vez que os parâmetros que utilizamos devem variar para outros corpora e, especialmente, pelo fato de termos realizados poucos testes para definir quais valores utilizaríamos para esses parâmetro, que são decisivos para a quantidade de palavras co-ocorrentes relevantes para os contextos de uso da palavra-alvo. Considerando-se tanto as vantagens quanto as limitações que observamos a partir dos resultados da clusterização, planejamos delinear um método sincrônico (que prescinde da documentação histórica das palavras) e computacional que permita distinguir casos de polissemia e de homonímia de forma mais sistemática e abrangendo uma maior quantidade de dados. Entendemos que um método dessa natureza pode ser de grade valia para os estudos do significado no nível lexical, permitindo o estabelecimento de um método objetivo e baseado em dados de uso da língua que vão além de exemplos pontuais. / The phenomenon of lexical ambiguity was the central topic of this research, especially with regard to relations between meanings of ambiguous graphic forms, and to patterns of distribution of the meanings of polysemous words in the language, that is, of words whose meanings are semantically related. This work is set on the interface between computational explorations of lexical ambiguity, specifically natural language processing, and theoretical investigations on the nature of research on the lexical meaning phenomenon. We assume the notions of polysemy and homonymy as corresponding, respectively, to the case of a word with multiple related meanings, and two (or more) words whose graphic forms coincide, but have unrelated meanings. The ultimate goal of this study was to confirm that the most polysemous words have meanings less evenly distributed in the corpus, with predominant meanings which occur more frequently. To examine these aspects, we implemented a word sense disambiguation algorithm, an adapted version of Lesk algorithm (Lesk, 1986; Jurafsky & Martin, 2000), chosen on the basis of the availability of language resources in Portuguese. From the hypothesis that the most frequent words in the language tend to be more polysemic, we selected from the corpus (Mac-Morpho) those words with the highest number occurrences. Considering our interest in content words and in cases of ambiguity more strictly to the semantic level, we decided to conduct the tests presented in this research only for nouns. The results obtained with the disambiguation algorithm implemented surpassed those of the baseline method based on the heuristics of the most frequent sense: we obtained 63% accuracy against 50% of baseline for all the disambiguated data. These results were obtained with the disambiguation procedure of pseudowords (formed at random), which used in cases where semantically annotated corpora are not available. However, due to the dependence of this disambiguation method on fixed inventories of meanings from dictionaries, we searched for alternative ways of categorizing the meanings of a word. Based on the work of Sproat & VanSanten (2001), we implemented a method for assigning numerical values that indicate how much one word is away from monosemy within a certain corpus. This measure, named by the authors of the original work as polysemy index, groups co-occurring words of the target noun according to their contextual similarities. We proposed in this paper the use of a second measure, mentioned by the authors as an example of the potential applications of the method to be explored: the clustering of the co-occurrent words based on their similarities of contexts of use. This second measurement is obtained so as to show the closeness of meanings and the amount of meanings that a word displays in the corpus. Some aspects pointed out in the results indicate the potential of the clustering method: the obtained co-occurring clusters are weighted, highlighting the most prominent groups of neighbors of the target word; the fact that the clusters aproximate from each other to each other on the basis of contextual similarity measures, which can be used to distinguish homonymic from polysemic trends. As an example, we have the clusters obtained for the word production, one referring to the idea of literary production, and the other referring to the notion of agricultural production. These two clusters exhibited considerable distance, standing in the range of what would be considered a case of polysemy, and both showed significant weights, that is, were composed of significant and distintictive words. We identified three main factors that have limited the analysis of the data: the political-journalistic bias of the corpus we use (Mac-Morpho) and the need for further testing by varying the selection parameters of relevant cooccurent words, since the parameters used shall vary for other corpora, and especially because of the fact that we conducted only a few tests to determine the values for these parameters, which are decisive for the amount of relevant co-occurring words for the target word. Considering both the advantages and the limitations we observe from the results of the clusterization method, we plan to design a synchronous (which dispenses with the historical documentation of the words) and, computational method to distinguish cases of polysemy and homonymy more systematically and covering a larger amount of data. We understand that a method of this nature can be invaluable for studies of the meaning on the lexical level, allowing the establishment of an objective method based on language usage data and, that goes beyond specific examples.

O fenômeno da ambiguidade lexical foi o tópico central desta pesquisa, especialmente no que diz respeito às relações entre acepções de formas gráficas ambíguas e aos padrões de distribuição de acepções de palavras polissêmicas na língua, isto é, de palavras cujas acepções são semanticamente relacionadas. Este trabalho situa-se como uma proposta de interface entre explorações computacionais da ambiguidade lexical, especificamente de processamento de linguagem natural, e investigações de cunho teórico sobre o fenômeno do significado lexical. Partimos das noções de polissemia e de homonímia como correspondentes, respectivamente, ao caso de uma palavra com múltiplas acepções relacionadas e ao de duas (ou mais) palavras cujas formas gráficas coincidem, mas que apresentam acepções não relacionadas sincronicamente. Como objetivo último deste estudo, pretendia-se confirmar se as palavras mais polissêmicas teriam acepções menos uniformemente distribuídas no corpus, apresentando acepções predominantes, que ocorreriam com maior frequência. Para analisar esses aspectos, implementamos um algoritmo de desambiguação lexical, uma versão adaptada do algoritmo de Lesk (Lesk, 1986; Jurafsky & Martin, 2000), escolhido com base nos recursos linguísticos disponíveis para o português. Tendo como hipótese a noção de que palavras mais frequentes na língua tenderiam a ser mais polissêmicas, selecionamos do corpus (Mac-Morpho) aquelas com maiores ocorrências. Considerando-se o interesse em palavras de conteúdo e em casos de ambiguidade mais estritamente em nível semântico, optamos por realizar os testes apresentados neste trabalho apenas para substantivos. Os resultados obtidos com o algoritmo de desambiguação que implementamos superaram o método baseline baseado na heurística da acepção mais frequente: obtivemos 63% de acertos contra 50% do baseline para o total dos dados desambiguados. Esses resultados foram obtidos através do procedimento de desambiguação de pseudo-palavras (formadas ao acaso), utilizado em casos em que não se tem à disposição corpora semanticamente anotados. No entanto, em razão da dependência de inventários fixos de acepções oriundos de dicionários, pesquisamos maneiras alternativas de categorizar as acepções de uma palavra. Tomando como base o trabalho de Sproat & VanSanten (2001), implementamos um método que permite atribuir valores numéricos que atestam o quanto uma palavra se afastou da monossemia dentro de um determinado corpus. Essa medida, cunhada pelos autores do trabalho original como índice de polissemia, baseia-se no agrupamento de palavras co-ocorrentes à palavra-alvo da desambiguação de acordo com suas similaridades contextuais. Propusemos, neste trabalho, o uso de uma segunda medida, mencionada pelos autores apenas como um exemplo das aplicações potenciais do método a serem exploradas: a clusterização de co-ocorrentes com base em similaridades de contextos de uso. Essa segunda medida é obtida de forma que se possa verificar a proximidade entre acepções e a quantidade de acepções que uma palavra exibe no corpus. Alguns aspectos apontados nos resultados indicam o potencial do método de clusterização: os agrupamentos de co-ocorrentes obtidos são ponderados, ressaltando os grupos mais proeminentes de vizinhos da palavra-alvo; o fato de que os agrupamentos aproximam-se uns dos outros por medidas de similaridade contextual, o que pode servir para distinguir tendências homonímicas ou polissêmicas. Como exemplo, temos os clusters obtidos para a palavra produção: um relativo à ideia de produção literária e outro relativo à de produção agrícola. Esses dois clusters apresentaram distanciamento considerável, situando-se na faixa do que seria considerado um caso de polissemia, e apresentaram ambos pesos significativos, isto é, foram compostos por palavras mais relevantes. Identificamos três fatores principais que limitaram as análises a partir dos dados obtidos: o viés político-jornalístico do corpus que utilizamos (Mac-Morpho) e a necessidade de serem feitos mais testes variando os parâmetros de seleção de coocorrentes, uma vez que os parâmetros que utilizamos devem variar para outros corpora e, especialmente, pelo fato de termos realizados poucos testes para definir quais valores utilizaríamos para esses parâmetro, que são decisivos para a quantidade de palavras co-ocorrentes relevantes para os contextos de uso da palavra-alvo. Considerando-se tanto as vantagens quanto as limitações que observamos a partir dos resultados da clusterização, planejamos delinear um método sincrônico (que prescinde da documentação histórica das palavras) e computacional que permita distinguir casos de polissemia e de homonímia de forma mais sistemática e abrangendo uma maior quantidade de dados. Entendemos que um método dessa natureza pode ser de grade valia para os estudos do significado no nível lexical, permitindo o estabelecimento de um método objetivo e baseado em dados de uso da língua que vão além de exemplos pontuais. / The phenomenon of lexical ambiguity was the central topic of this research, especially with regard to relations between meanings of ambiguous graphic forms, and to patterns of distribution of the meanings of polysemous words in the language, that is, of words whose meanings are semantically related. This work is set on the interface between computational explorations of lexical ambiguity, specifically natural language processing, and theoretical investigations on the nature of research on the lexical meaning phenomenon. We assume the notions of polysemy and homonymy as corresponding, respectively, to the case of a word with multiple related meanings, and two (or more) words whose graphic forms coincide, but have unrelated meanings. The ultimate goal of this study was to confirm that the most polysemous words have meanings less evenly distributed in the corpus, with predominant meanings which occur more frequently. To examine these aspects, we implemented a word sense disambiguation algorithm, an adapted version of Lesk algorithm (Lesk, 1986; Jurafsky & Martin, 2000), chosen on the basis of the availability of language resources in Portuguese. From the hypothesis that the most frequent words in the language tend to be more polysemic, we selected from the corpus (Mac-Morpho) those words with the highest number occurrences. Considering our interest in content words and in cases of ambiguity more strictly to the semantic level, we decided to conduct the tests presented in this research only for nouns. The results obtained with the disambiguation algorithm implemented surpassed those of the baseline method based on the heuristics of the most frequent sense: we obtained 63% accuracy against 50% of baseline for all the disambiguated data. These results were obtained with the disambiguation procedure of pseudowords (formed at random), which used in cases where semantically annotated corpora are not available. However, due to the dependence of this disambiguation method on fixed inventories of meanings from dictionaries, we searched for alternative ways of categorizing the meanings of a word. Based on the work of Sproat & VanSanten (2001), we implemented a method for assigning numerical values that indicate how much one word is away from monosemy within a certain corpus. This measure, named by the authors of the original work as polysemy index, groups co-occurring words of the target noun according to their contextual similarities. We proposed in this paper the use of a second measure, mentioned by the authors as an example of the potential applications of the method to be explored: the clustering of the co-occurrent words based on their similarities of contexts of use. This second measurement is obtained so as to show the closeness of meanings and the amount of meanings that a word displays in the corpus. Some aspects pointed out in the results indicate the potential of the clustering method: the obtained co-occurring clusters are weighted, highlighting the most prominent groups of neighbors of the target word; the fact that the clusters aproximate from each other to each other on the basis of contextual similarity measures, which can be used to distinguish homonymic from polysemic trends. As an example, we have the clusters obtained for the word production, one referring to the idea of literary production, and the other referring to the notion of agricultural production. These two clusters exhibited considerable distance, standing in the range of what would be considered a case of polysemy, and both showed significant weights, that is, were composed of significant and distintictive words. We identified three main factors that have limited the analysis of the data: the political-journalistic bias of the corpus we use (Mac-Morpho) and the need for further testing by varying the selection parameters of relevant cooccurent words, since the parameters used shall vary for other corpora, and especially because of the fact that we conducted only a few tests to determine the values for these parameters, which are decisive for the amount of relevant co-occurring words for the target word. Considering both the advantages and the limitations we observe from the results of the clusterization method, we plan to design a synchronous (which dispenses with the historical documentation of the words) and, computational method to distinguish cases of polysemy and homonymy more systematically and covering a larger amount of data. We understand that a method of this nature can be invaluable for studies of the meaning on the lexical level, allowing the establishment of an objective method based on language usage data and, that goes beyond specific examples.

Word sense disambiguation (WSD) is the process of computationally identifying and labeling poly- semous words in context with their correct meaning, known as a sense. WSD is riddled with various obstacles that must be overcome in order to reach its full potential. One of these problems is the aspect of the representation of word meaning. Traditional WSD algorithms make the assumption that a word in a given context has only one meaning and therfore can return only one discrete sense. On the other hand, a novel approach is that a given word can have multiple senses. Studies on graded word sense assignment (Erk et al., 2009) as well as in cognitive science (Hampton, 2007; Murphy, 2002) support this theory. It has therefore been adopted in a novel, paraphrasing system which performs word sense disambiguation by returning a probability distribution over potential paraphrases (in this case synonyms) of a given word. However, it is unknown how well this type of algorithm fares against the traditional one. The current study thus examines if and how it is possible to make a comparison of the two. A method of comparison is evaluated and subsequently rejected. Reasons for this as well as suggestions for a fair and accurate comparison are presented.

This study investigated the effects of multiple textual encounters of words and textual encounters of words supplemented with pictorial glosses upon the ability of a learner of French to infer additional word senses—senses of target words that were not previously encountered. Twenty-nine participants were randomly divided into two groups, Groups A and B, and were subjected to two treatments, one in which the subjects encountered target words textually twice (Repeated Textual Encounters, RTE) and one in which the subjects encountered target words once textually and once pictorially (Pictorial Encounter, PE). Before the administration of the two vocabulary-learning treatments the participants completed a vocabulary pretest on the target words to establish a baseline of knowledge. At the conclusion of the vocabulary pretest, Group A read a French fairy tale encountering half of the target words using the RTE treatment while encountering the other half of the target words using the PE treatment. Although Group B read the same French fairy tale, they did not receive the same treatment for the same words. Specifically, the target words that those in Group A encountered using the RTE treatment were encountered by those in Group B using the PE treatment, and vise versa for the other treatment. Immediately following the treatments the participants completed a vocabulary recall test wherein the participants demonstrated their ability to infer additional senses of the target words in addition to recall original senses of target words as encountered in the text. Vocabulary gains were used as data to determine the participants' ability to infer additional word senses and recall original word senses. Results from t tests indicate that both treatments have a significant impact upon the learner's ability to infer additional word senses as well as recall original senses. Furthermore, results from analysis on the data gathered for individual words show that the treatments had a significant effect on learners inferring and recalling the senses of certain words over others. Results did not determine, however, which treatment was more effective than the other for learners to infer additional senses of words or to recall original word senses.

Semantic distance is a measure of how close or distant in meaning two units of language are. A large number of important natural language problems, including machine translation and word sense disambiguation, can be viewed as semantic distance problems. The two dominant approaches to estimating semantic distance are the WordNet-based semantic measures and the corpus-based distributional measures. In this thesis, I compare them, both qualitatively and quantitatively, and identify the limitations of each. This thesis argues that estimating semantic distance is essentially a property of concepts (rather than words) and that two concepts are semantically close if they occur in similar contexts. Instead of identifying the co-occurrence (distributional) profiles of words (distributional hypothesis), I argue that distributional profiles of concepts (DPCs) can be used to infer the semantic properties of concepts and indeed to estimate semantic distance more accurately. I propose a new hybrid approach to calculating semantic distance that combines corpus statistics and a published thesaurus (Macquarie Thesaurus). The algorithm determines estimates of the DPCs using the categories in the thesaurus as very coarse concepts and, notably, without requiring any sense-annotated data. Even though the use of only about 1000 concepts to represent the vocabulary of a language seems drastic, I show that the method achieves results better than the state-of-the-art in a number of natural language tasks. I show how cross-lingual DPCs can be created by combining text in one language with a thesaurus from another. Using these cross-lingual DPCs, we can solve problems in one, possibly resource-poor, language using a knowledge source from another, possibly resource-rich, language. I show that the approach is also useful in tasks that inherently involve two or more languages, such as machine translation and multilingual text summarization. The proposed approach is computationally inexpensive, it can estimate both semantic relatedness and semantic similarity, and it can be applied to all parts of speech. Extensive experiments on ranking word pairs as per semantic distance, real-word spelling correction, solving Reader's Digest word choice problems, determining word sense dominance, word sense disambiguation, and word translation show that the new approach is markedly superior to previous ones.

Semantic distance is a measure of how close or distant in meaning two units of language are. A large number of important natural language problems, including machine translation and word sense disambiguation, can be viewed as semantic distance problems. The two dominant approaches to estimating semantic distance are the WordNet-based semantic measures and the corpus-based distributional measures. In this thesis, I compare them, both qualitatively and quantitatively, and identify the limitations of each. This thesis argues that estimating semantic distance is essentially a property of concepts (rather than words) and that two concepts are semantically close if they occur in similar contexts. Instead of identifying the co-occurrence (distributional) profiles of words (distributional hypothesis), I argue that distributional profiles of concepts (DPCs) can be used to infer the semantic properties of concepts and indeed to estimate semantic distance more accurately. I propose a new hybrid approach to calculating semantic distance that combines corpus statistics and a published thesaurus (Macquarie Thesaurus). The algorithm determines estimates of the DPCs using the categories in the thesaurus as very coarse concepts and, notably, without requiring any sense-annotated data. Even though the use of only about 1000 concepts to represent the vocabulary of a language seems drastic, I show that the method achieves results better than the state-of-the-art in a number of natural language tasks. I show how cross-lingual DPCs can be created by combining text in one language with a thesaurus from another. Using these cross-lingual DPCs, we can solve problems in one, possibly resource-poor, language using a knowledge source from another, possibly resource-rich, language. I show that the approach is also useful in tasks that inherently involve two or more languages, such as machine translation and multilingual text summarization. The proposed approach is computationally inexpensive, it can estimate both semantic relatedness and semantic similarity, and it can be applied to all parts of speech. Extensive experiments on ranking word pairs as per semantic distance, real-word spelling correction, solving Reader's Digest word choice problems, determining word sense dominance, word sense disambiguation, and word translation show that the new approach is markedly superior to previous ones.