In bioinformatics there exist research topics that cannot be uniquely characterized by a set of key words because relevant key words are (i) also heavily used in other contexts and (ii) often omitted in relevant documents because the context is clear to the target audience. Information retrieval interfaces such as entrez/Pubmed produce either low precision or low recall in this case. To yield a high recall at a reasonable precision, the results of a broad information retrieval search have to be filtered to remove irrelevant documents. We use automated text categorization for this purpose. In this study we use the topic of conserved secondary RNA structures in viral genomes as running example. Pubmed result sets for two virus groups, Picornaviridae and Flaviviridae, have been manually labeled by human experts. We evaluated various classifiers from the Weka toolkit together with different feature selection methods to assess whether classifiers trained on documents dedicated to one virus group can be successfully applied to filter literature on other virus groups. Our results indicate that in this domain a bibliographic search tool trained on a reference corpus may significantly reduce the amount of time needed for extensive literature recherches.

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no / In three experiments we investigated the dynamics of impression formation when perceivers encounter unsurprising (e.g. male mechanic) versus surprising (e.g. female mechanic) social category conjunctions. In Experiment 1, participants took longer to form an impression of targets described using a surprising versus an unsurprising conjunction of categorizations. In Experiment 2, we investigated the stages during which impressions of category conjunctions are formed. While unsurprising category combinations were characterized with reference to ‘constituent’ stereotypic traits, surprising combinations were characterized initially by stereotypic traits but later by ‘emergent’ impressions. In Experiment 3, we investigated motivational states that drive the dynamics of category conjunction. We found that higher Personal Need for Structure (PNS) predicted the use of more emergent and fewer constituent attributes in the impressions formed of surprising combinations. Across all three experiments, more ‘causal attributes’ were used in descriptions of the surprising combination. We discuss the implications of these findings for developing a model of the dynamics and composition of social category conjunctions.

No / There has been an increased interest in video indexing and retrieval in recent years. In this work, indexing and retrieval system of the visual contents is based on feature extracted from the compressed domain. Direct possessing of the compressed domain spares the decoding time, which is extremely important when indexing large number of multimedia archives. A fuzzy-categorizing structure is designed in this paper to improve the retrieval performance. In our experiment, a database that consists of basketball videos has been constructed for our study. This database includes three categories: full-court match, penalty and close-up. First, spatial and temporal feature extraction is applied to train the fuzzy membership functions using the minimum entropy optimal algorithm. Then, the max composition operation is used to generate a new fuzzy feature to represent the content of the shots. Finally, the fuzzy-based representation becomes the indexing feature for the content-based video retrieval system. The experimental results show that the proposal algorithm is quite promising for semantic-based video retrieval.

Perceptual categorization involves integrating bottom-up sensory information with top-down knowledge which is based on prior experience. Bottom-up information comes from the external world and visual saliency is a type of bottom-up information that is calculated on the differences between the visual characteristics of adjacent spatial locations. There is currently a related debate in municipal law enforcement communities about which are more ‘visible’: white police cars or black and white police cars. Municipalities do not want police cars to be hit by motorists and they also want police cars to be seen in order to promote a public presence. The present study used three behavioral experiments to investigate the effects of visual saliency on object detection and categorization. Importantly, the results indicated that so-called ‘object detection’ is not a valid construct. Rather than identifying objectness or objecthood prior to categorization, object categorization is an obligatory process, and object detection is a postcategorization decision with higher salience objects being categorized easier than lower salience objects. An additional experiment was conducted to examine the features that constitute a police car. Based on salience alone, black and white police cars were better categorized than white police cars and light bars were slightly more important police car defining components than markings.

published_or_final_version / Psychology / Doctoral / Doctor of Philosophy

This dissertation consists of a review of the N2 component of the ERP and five experiments investigating the role of complex visual object categorization in modulating the N2 and two other ERP components: the P300, and a late prefrontal positivity. In the review, we focus on paradigms that elicit N2 components with an anterior scalp distribution, namely cognitive control, novelty, and sequential matching, arguing that the anterior N2 should be divided into separate control- and mismatch-related subcomponents. The experiments manipulated categorical typicality and the presence of conflicting information as participants categorized multi-featured artificial animals. In Experiments 1 and 2, rule-irrelevant features were correlated with particular categories during training. During transfer, participants applied a one- dimensional rule to stimuli with category-congruent, category-incongruent, or novel rule-irrelevant features. Category-incongruent and novel features delayed RT and P300 latency, but had no effect on the N2. Experiment 3 used a two-dimensional rule to create conflict between rule-relevant features. Conflict resulted in prolonged RTs, P300 latency, and larger amplitudes of a prefrontal positive component, but had no impact on the N2. Novel features did enhance the N2 relative to frequent features. In Experiments 4 and 5, participants categorized stimuli using a more complex three dimensional rule. Conflicting stimuli shared two features with one prototype and one feature with a second prototype while prototypes contained no conflicting information. A third category contained stimuli with either common or novel features. Again, perceptual novelty, but not conflict, increased the amplitude of the N2. Compared to prototypes, stimuli with conflicting information slowed reaction times but had no effect on P300 latency, instead enhancing a late prefrontal positive component. These results suggest limitations on the generality of the N2's sensitivity to conflicting information, while confirming its sensitivity to attended visual novelty. We suggest that, while P300 latency tracks stimulus evaluation time, application of a complex categorization rule requires a later stage of evaluation involving prefrontal cortex. In very complex rules, computations indexed by the P3 may be terminated early in favor of computations in PFC.

All these four factors influence the degree of CP. In the discussion, both general auditory processing and language specific processing are suggested to be responsible for the various types of exhibition of CP, although they have different weights for different factors. Different patterns of CP were also observed in three temporal stages due to different weights of these two types of processing. In summary, a multistage model which includes both general auditory processing and language specific processing is proposed to explain the CP of lexical tones. This model improves previous models by proposing that the weights of these two types of processing in speech perception depend on the types of factors, and the temporal processing stages. / Finally, for the first time in the literature, the thesis also reported that even though a tone contrast (i.e., level vs. rising) is present in both tone systems, the same contrast is perceived differently by the two groups of subjects by virtue of their different language experiences. / Four factors were studied. They were (1) intrinsic acoustic properties of pitch contours by comparison between continua of level tones and contour tones; (2) positions of target syllables relative to context (without contextual sentence, at the beginning and at the end of the contextual sentence); (3) language backgrounds by comparison between listeners with different tone experiences; and (4) carrier syllables (real word, non word, and nonspeech). Three temporal stages were studied in the same experimental paradigm. They were (1) the preattentive stage investigated through the mismatch negativity (MMN); (2) the attentive stage investigated through the P300; and (3) the overt response stage investigated through the hit rate data. / Pitch contour or its acoustic correlate, fundamental frequency (F0), distinguishes lexical meanings in tone languages. Two topics on CP of lexical tones were studied in the thesis: (1) the factors influencing CP, and (2) the temporal process of CP. These two topics were investigated through both behavioral and event-related-potential (ERP) methods on Cantonese and Mandarin tones. / Speech sounds vary across different conditions and subjects; nevertheless, listeners perceive the phonemes without difficulties. Categorical perception (CP) occurs when listeners map the varying speech sounds into discrete phonemic categories. In CP, to discriminate a pair of stimuli that cross a category boundary is much easier than those that lie within the same category, even though both pairs are separated by an equal physical difference. CP is one of the important properties essential for speech perception. / Zheng, Hongying. / Adviser: William Shi-Yuan Wang. / Source: Dissertation Abstracts International, Volume: 72-04, Section: A, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 179-194). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese; appendix 2 in Chinese.

This experiment investigated the processes underlying similarity-based free categorization. Of particular interest was how temporal distance between similar objects affects the likelihood that people will put them into the same novel category. Participants engaged in a free categorization task referred to as binomial labeling. This task required participants to generate a two-part label (A1, B1, C1, etc.) indicating family (superordinate) and species (subordinate) levels of categorization for each object in a visual display. Participants were shown the objects one at a time in a sequential presentation; after labeling each object, they were asked to describe the similarity between that object and previous objects by selecting one of five choices from a drop down menu. Our main prediction was that temporal distance should affect categorization, specifically, that people should be less likely to give two identical objects the same category label the farther apart they are shown in the display. The primary question being addressed in this study was whether the effects of distance are due to a decreased likelihood of remembering the first object when labeling the second (what we refer to as a stage 1 or sampling effect) or to factors during the actual comparison itself (a stage 2 or decision effect)? Our results showed a significant effect of distance on both the likelihood of giving identical objects the same label as well as on the likelihood of mentioning the first object when labeling the second object in an identical pair. Specifically, as the distance between two identical objects increased, the likelihood of giving them the same label, as well as mentioning their similarity, both decreased. Importantly, the decreased probability of giving the second object the same label seemed entirely due to the decreased probability of remembering (sampling) the first object, as indicated by the menu responses. These results provide strong support for the idea that the effect of temporal distance on free categorization is mainly due to stage 1 factors, specifically to its effect on the availability of the first instance in memory when labeling the second. No strong evidence was found in this experiment supporting a separate distance effect at the comparison-decision stage (i.e., stage 2).