Testing the Bayesian brain hypothesis in visual perception

Dissertation supervisor: Dr. Jeffrey N. Rouder.Includes vita.Bayesian ideal observer theory describes perception as an ideal integration of sensory information with prior knowledge to produce optimal responses. Bayesian ideal perception models are popular in sensory domains; however, these models often prove unfalsifiable because of excessive distributional assumptions and post-hoc estimation of participant beliefs. Three visual perception tasks were designed to test Bayesian ideal observer theory under minimal assumptions using the Bayesian Decision Theory framework. Prior distributions of stimuli were specified, likelihoods were manipulated across four stimulus reliability levels, and loss functions were established so that participants could choose posterior point estimates which minimize loss. In each experiment, a Bayesian ideal observer model was fit against a Bayesian posterior matching model (adapted from the probability matching phenomenon) and one or more non-Bayesian mixture models. Results from two experiments in which participants were making location-based judgments overwhelmingly supported the posterior matching models. Data from a third experiment in which participants made estimations about the number of items in an array were fit best by a non-Bayesian mixture model. Overall, Bayesian ideal observer theory was not supported in three experiments of visual perception.Includes bibliographical references (pages 128-134)

Exploring the structure of cognitive processes: discrete and continuous theories of memory and perception

Title from PDF of title page (University of Missouri--Columbia, viewed on September 12, 2013).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Thesis advisor: Dr. Jeffrey N. RouderIncludes bibliographical references.M.A. University of Missouri--Columbia 2013.Dissertations, Academic -- University of Missouri--Columbia -- Psychology."May 2013"Cognitive psychologists often debate whether cognitive processes such as recognition memory and visual perception are better described as continuous or discrete. Much of the literature is dominated by continuous latent-strength models such as signal detection theory. Here the author sought to test the effectiveness of discrete-state models at predicting performance on cognitive tasks. Thirty-nine participants completed Experiment 1, which analyzed recognition memory and visual word identification performance in two-alternative forced choice tasks. Fifty participants completed Experiment 2, which focused on word identifi cation in both two-choice and one-choice designs. Data were analyzed via maximum likelihood estimation for comparable discrete-state and latent-strength models for all participants. The discrete-state models outperformed latent-strength models for the majority of participants in both tasks of both experiments. Evidence for discrete states was especially strong in two-choice word identification tasks. The results indicate that discrete-state models should not be ignored in cognitive processing, as they provide a good account of data in recognition memory and word identification tasks

Metacognition of intentions in mindfulness and hypnosis

In a famous series of experiments, Libet investigated the subjective timing of awareness of an intention to move, a task that can be considered a metacognitive judgement. The ability to strategically produce inaccurate metacognitions about intentions has been postulated to be central to the changes in judgements of agency common to all hypnotic responding. Therefore, differences in hypnotisability may be reflected in Libet’s measure. Specifically, the ability to sustain inaccurate judgements of agency displayed by highly hypnotisable people may result from their having coarser higher order representations of intentions. They therefore should report a delayed time of intention relative to less hypnotisable individuals. Conversely, mindfulness practice aims at accurate metacognition, including of intentions, and may lead to the development of finer grained higher order representations of intending. Thus, the long-term practice of mindfulness may produce an earlier judgement of the time of an intention. We tested these groups using Libet’s task, and found that, consistent with predictions, highly hypnotisable people reported a later time of intention than less hypnotisable people and meditators an earlier time than non-meditators. In a further two studies we replicated the finding that hypnotisable people report later awareness of a motor intention and additionally found a negative relationship between trait mindfulness and this measure. Based on these findings, we argue that hypnotic response and meditation involve opposite processes

FIJAc: Fright and illness in highland Yemen

Sudden fright, 'fijac', has played an important role in the traditional explanatory models of illness experiences in highland Yemen. Fijac is quite similar to other examples of the fright illness taxon in that it is a folk-illness category that is attributed to a wide variety of underlying conditions. It is argued that given the extremely labile symptomatology, fijac, like other examples of the fright illness taxon, does not constitute a culture-bound psychiatric syndrome. Based on analysis of case studies and preliminary survey data, fijac appears to be much more common among folk etiologies offered by Yemeni women than men. It is suggested that this social profile might be explained by changes in the distribution of medical knowledge in Yemen. With the rapid rate of social change and the increased exposure to cosmopolitan medicine resulting from internal development of cosmopolitan health care and international labor migration, men have supplemented their traditional explanatory models with alternatives drawn from cosmopolitan medicine. Succumbing to illness as a result of fright is contradictory to the male ideal of the courageous tribesman; alternative explanatory models that do not challenge this ideal self predominate. By contrast, the Yemeni value system defines women and children as vulnerable and weak; therefore, being subject to the impact of fright is consistent with youth and the cultural definition of the female self.Middle East Yemen folk illness medical anthropology

Language Names and Norms in Bosnia and Herzegovina.

The institutionalization of separate standard varieties for Bosnian, Croatian, and Serbian in the 1990s was hailed by many Bosnians as the long-denied recognition of the Bosnian idiom as distinct from the Serbian and Croatian varieties it had so often been subordinated under. Yet the accompanying codification of Bosnian standard language forms has been highly controversial in Bosnia, and debates continue today about how to define the Bosnian language. My dissertation explores the paradox that while many Bosnians support the Bosnian language as a name, they often do not support it as a norm. To explore this paradox, I undertook 12 months of fieldwork in four different middle schools in Bosnia. Education is a domain in which linguistic norms are highlighted. In Bosnia, it is also an area in which language variation is deemed to be particularly problematic by observers, participants, and commentators both locally and abroad. The decentralized nature of education in Bosnia means that classrooms are often ethnically segregated and curricula in use across the country are not harmonized. Language standardization has often been analyzed as a state-sponsored process that works through official institutions to reduce heterogeneity and promote uniform understandings of linguistic forms and their semiotic meanings. This dissertation explores ongoing language standardization campaigns in Bosnia and Herzegovina and argues that traditional ways of understanding the role of institutions in language standardization don’t explain why standardization has been so unsuccessful in the post-war Bosnian state. My research challenges the idea that institutions must be engaged in drawing rigid us/them boundaries to be thought of as representative or legitimate, instead pointing to the possibility that ambiguity can be a marker of legitimacy rather than a threat to it. This dissertation explores how ideologies of heterogeneity and choice in language work against the imposition of a standard norm at the same time as European aspirations and ideas about post-socialist normalcy push many Bosnians to believe their country should have such a standard. The resulting tension is the space in which choice between standard variants takes on social meaning and contributes to emerging definitions of what it means to be Bosnian.Ph.D.AnthropologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/86415/1/kirstisw_1.pd

Bayesian analysis of factorial designs

This article provides a Bayes factor approach to multiway analysis of variance (ANOVA) that allows researchers to state graded evidence for effects or invariances as determined by the data. ANOVA is conceptualized as a hierarchical model where levels are clustered within factors. The development is comprehensive in that it includes Bayes factors for fixed and random effects and for within-subjects, between-subjects, and mixed designs. Different model construction and comparison strategies are discussed, and an example is provided. We show how Bayes factors may be computed with BayesFactor package in R and with the JASP statistical package