From partners to populations:A hierarchical Bayesian account of coordination and convention

Languages are powerful solutions to coordination problems: they provide stable, shared expectations about how the words we say correspond to the beliefs and intentions in our heads. Yet language use in a variable and non-stationary social environment requires linguistic representations to be flexible: old words acquire new ad hoc or partner-specific meanings on the fly. In this paper, we introduce CHAI (Continual Hierarchical Adaptation through Inference), a hierarchical Bayesian theory of coordination and convention formation that aims to reconcile the long-standing tension between these two basic observations. We argue that the central computational problem of communication is not simply transmission, as in classical formulations, but continual learning and adaptation over multiple timescales. Partner-specific common ground quickly emerges from social inferences within dyadic interactions, while community-wide social conventions are stable priors that have been abstracted away from interactions with multiple partners. We present new empirical data alongside simulations showing how our model provides a computational foundation for several phenomena that have posed a challenge for previous accounts: (1) the convergence to more efficient referring expressions across repeated interaction with the same partner, (2) the gradual transfer of partner-specific common ground to strangers, and (3) the influence of communicative context on which conventions eventually form.Comment: In press at Psychological Revie

Colour Communication Within Different Languages

For computational methods aiming to reproduce colour names that are meaningful to speakers of different languages, the mapping between perceptual and linguistic aspects of colour is a problem of central information processing. This thesis advances the field of computational colour communication within different languages in five main directions. First, we show that web-based experimental methodologies offer considerable advantages in obtaining a large number of colour naming responses in British and American English, Greek, Russian, Thai and Turkish. We continue with the application of machine learning methods to discover criteria in linguistic, behavioural and geometric features of colour names that distinguish classes of colours. We show that primary colour terms do not form a coherent class, whilst achromatic and basic classes do. We then propose and evaluate a computational model trained by human responses in the online experiment to automate the assignment of colour names in different languages across the full three-dimensional colour gamut. Fourth, we determine for the first time the location of colour names within a physiologically-based cone excitation space through an unconstrained colour naming experiment using a calibrated monitor under controlled viewing conditions. We show a good correspondence between online and offline datasets; and confirm the validity of both experimental methodologies for estimating colour naming functions in laboratory and real-world monitor settings. Finally, we present a novel information theoretic measure, called dispensability, for colour categories that predicts a gradual scale of basicness across languages from both web- and laboratory- based unconstrained colour naming datasets. As a result, this thesis contributes experimental and computational methodologies towards the development of multilingual colour communication schemes

Motion Event Expression in Bilingual First Language Acquisition

The thesis explores the implications of Talmy’s typology of motion expression (Talmy 1985, 2000a,b) for bilingual first language acquisition of English (satellite-framing) and French (verb-framing), addressing the following question: How does the expression of motion develop in simultaneous bilingual children in comparison to monolinguals? The particular focus of this study is on the role of crosslinguistic interactions and the extent to which their occurrence and directionality are affected by language-specific properties, children’s age and the factor of task complexity. The thesis pursues two goals. First, it aims to contribute to the growing understanding of the role of languagespecific factors in the acquisition process (e.g. Allen et al. 2007, Choi and Bowerman 1991, Hickmann et al. 2009a). Secondly, by testing various proposals regarding crosslinguistic interactions (Gawliĵek-Maiwald and Tracy 1996, Müller and Hulk 2001, Toribio 2004), it endeavours to shed light on bilingual speech production processes. Oral event descriptions elicited by means of short video clips from bilingual and monolingual children aged 4 to 10 years are analysed and compared across two production tasks of varying semantic complexity: a simpler voluntary motion task, showing agents performing spontaneous movements along various paths, and a more complex caused motion task, portraying a human agent causing the displacement of various objects in different manners along various paths. Bilinguals’ event descriptions are analysed quantitatively and qualitatively in relation to monolingual English and French control groups across various aspects of verbalisation: (i) the linguistic devices used for information encoding (information packaging), (ii) the number of information components expressed (semantic density), and (iii) their syntactic complexity and compactness (utterance architecture). The results indicate both parallels and differences to monolingual performance patterns. Although bilinguals’ event descriptions generally follow the typological tendencies characterising monolinguals’ English and French verbalisation tendencies, they also exhibit significant departures from the monolingual range in both languages, at all tested ages and in both production tasks. However, these differences are most prominent in children’s French and in the caused motion task. In this context, bilinguals display a striking preference for satellite-framing encoding options, resulting both in the overuse of crosslinguistically overlapping packaging strategies and in qualitatively idiosyncratic extensions of French locative satellites. Syntactically, bilinguals show a strong tendency to use compact and simple structures (lacking subordination) compared to French monolinguals. An unexpected finding concerns the occurrence of a number of divergent production phenomena that are shared by bilinguals’ productions in both languages and tasks, and suggest a bilingual-specific pattern of use. The findings are discussed in the context of recent proposals regarding crosslinguistic interactions in simultaneous bilingualism. The persistence of bilingual-specific effects even at age 10 suggests that cross-linguistic interactions characterise bilinguals’ verbal behaviour throughout language development. This supports the notion that the bilingual is a unique speaker-hearer in his own right (Grosjean 1985, 2008). With regard to the impact of typological and general determinants, the findings indicate that bilinguals’ verbalisation choices are guided by a complex interplay of event-specific factors and the perceived overlap of language-specific properties of both languages

Referring Expression Generation in Situated Interaction

While most current frameworks for reference handling are based on binary truth-theoretic knowledge representation, in this thesis I argue for a perspective on reference which emphasises the collaborative nature of reference. I present the Probabilistic Reference And GRounding mechanism (PRAGR) which uses flexible concept assignment based on vague property models and situational context in order to maximise the chance of communicative success. I demonstrate that PRAGR is capable of dealing with several property domains with different internal structures, such as graded adjectives, colour, shape, projective terms, and projective regions. Further, I show that PRAGR is fit to handle in an integrated fashion the most relevant challenges of Referring Expression Generation, in particular graded properties, spatial relations, and salience effects. In three empirical evaluation studies, I demonstrate the usefulness of PRAGR for situated referential communication

The salience of the hues: colour cognition from an indigenous Australian perspective

Does natural language determine the way we think? If the so-called Sapir-Whorf hypothesis of linguistics were true then colour categorization would be an entirely arbitrary process dependant entirely on the language that we speak. For a while in academic circles this was the received wisdom: The fact that English had 11 colour terms and Dugum Dani (from Papua New Guinea) had only two was a factor attributed to the language in use. In 1969, Brent Berlin and Paul Kay ushered in the paradigm shift of Basic Colour Terms, a theory that defined the structure and evolution of colour terms in cultures (Berlin and Kay, 1969). According to this theory there was a neurophysiological basis for colour categorization, which implied that all human beings had the potential to see the same colours but naming the categories was an evolutionary process tied into the technological sophistication of a society. Language in other words played little or no part in colour perception. The initial theory was highly controversial with the demand growing for verification of the initial findings. To address the contentious issues surrounding Berlin and Kay’s theory, a project entitled the World Colour Survey was initiated with the goal of determining colour categorization patterns within 110 pre-literate cultures across the globe. This project has spanned more than 30 years with a definitive publication of the results still in the works. The current PhD project, which has been in progress since the dawn of time, involves an independent analysis and interpretation of the indigenous Australian component of the World Colour Survey raw data on colour categorization. It is both an exercise in secondary analysis as a research method and a tangential meditation on the ambiguity of knowledge that can be derived from extant data sets

Language production in Parkinson’s disease : an investigation into the characteristics and underlying cognitive and linguistic mechanisms

Research into language alteration in Parkinson’s Disease (PD) remains relatively limited. Findings to date indicate that both a specific verb processing deficit and altered sentence construction can present as part of the symptom profile. However, questions regarding the underlying nature of the verb processing deficit observed remain and, as far as can be established, no studies have explicitly explored whether the altered verb processing evidenced may be underpinning the observed alteration in measures of sentence construction. This thesis reports on the findings from four component studies, each addressing an identified gap within the current literature relating to verb and sentence processing. Of interest within the first two experimental research questions was the influence of the verbs semantic and grammatical characteristics on retrieval within both a single word and sentence context, and on various measures of sentence construction. In the main, the pattern of performance did not vary between individuals with PD and controls. Average pause length was found to be longer in sentences produced by individuals with PD, however, was not influenced by the verb’s characteristics. The third experimental question was concerned with investigating sentence production within tasks which varied in their nature and linguistic demands. Again, performance was largely comparable between groups, with the exception of average pause length. Whilst pauses were found to be longer in PD, this was not influenced by the demands of the task. Finally, exploratory correlational analyses were conducted to explore the relationship between the linguistic measures taken, and measures of various cognitive abilities. Patterns of association varied between the groups, indicating a complex relationship between language and cognitive measures. The majority of findings went against the predictions made. Collectively, findings indicate that, when verb processing is unimpaired in PD and cognitive functioning of a comparative level to controls, sentence construction is largely unimpaired.Research into language alteration in Parkinson’s Disease (PD) remains relatively limited. Findings to date indicate that both a specific verb processing deficit and altered sentence construction can present as part of the symptom profile. However, questions regarding the underlying nature of the verb processing deficit observed remain and, as far as can be established, no studies have explicitly explored whether the altered verb processing evidenced may be underpinning the observed alteration in measures of sentence construction. This thesis reports on the findings from four component studies, each addressing an identified gap within the current literature relating to verb and sentence processing. Of interest within the first two experimental research questions was the influence of the verbs semantic and grammatical characteristics on retrieval within both a single word and sentence context, and on various measures of sentence construction. In the main, the pattern of performance did not vary between individuals with PD and controls. Average pause length was found to be longer in sentences produced by individuals with PD, however, was not influenced by the verb’s characteristics. The third experimental question was concerned with investigating sentence production within tasks which varied in their nature and linguistic demands. Again, performance was largely comparable between groups, with the exception of average pause length. Whilst pauses were found to be longer in PD, this was not influenced by the demands of the task. Finally, exploratory correlational analyses were conducted to explore the relationship between the linguistic measures taken, and measures of various cognitive abilities. Patterns of association varied between the groups, indicating a complex relationship between language and cognitive measures. The majority of findings went against the predictions made. Collectively, findings indicate that, when verb processing is unimpaired in PD and cognitive functioning of a comparative level to controls, sentence construction is largely unimpaired