Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Search Results

Now showing 1 - 10 of 25

Relative Salience of Envelope and Fine Structure Cues in Zebra Finch Song
(2010) Vernaleo, Beth A.; Dooling, Robert J.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This dissertation examines the perceptual salience of several acoustic cues in zebra finch song. Birdsong has long served as an animal model of speech development. Both are learned during a sensitive period, and require auditory feedback for learning and maintenance. Zebra finch song is commonly studied due to its stereotyped nature. Song syllables are complex, containing multiple cues that are modulated over millisecond time scales. Using psychoacoustic methods, male zebra finches were tested on discrimination of changes to their own and conspecific songs. Females and budgerigars were also tested, since they have auditory experience with song, but do not sing. Three types of synthetic songs were created to determine which acoustic cues in song were most salient to birds. Same-seed noise songs were made of syllable envelopes filled with the same piece of random Gaussian noise. This removed spectral structure but kept song envelope cues intact. Random noise songs were made of each syllable envelope filled with a unique piece of noise. This provided more complex fine structure to the same song envelope. Lastly, Schroeder songs were made of Schroeder harmonic waveforms with the same duration as song syllables. In Schroeder waveforms, spectrum and envelope are constant, but phase changes occur across frequencies. Two types of song changes were tested: single interval duration doublings and single syllable reversals. All birds were much more sensitive to syllable changes than to interval changes. For natural song, there was a duration effect on performance for male zebra finches only. Performance on syllable reversals shorter than 100 milliseconds was positively correlated with syllable duration. In Schroeder song, where only fine temporal structure changes with reversal, all three groups showed a duration effect. Thus, females and budgerigars may focus less on fine structure in natural song than males. In the absence of song spectral structure, birds relied on syllable envelope cues for reversal discrimination. Thus, removal of a single cue from song did not greatly affect reversal discrimination. However, birds performed best when all cues were present. This is reminiscent of human speech, in which multiple redundant cues are used for speech recognition.
The structure and perception of budgerigar (Melopsittacus undulatus) warble songs
(2009) Tu, Hsiao-Wei; Dooling, Robert J; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The warble song of male budgerigars (Melopsittacus undulatus) is an extraordinarily complex, multi-syllabic, learned vocalization that is produced continuously in streams lasting from a few seconds to a few minutes without obvious repetition of particular patterns. As a follow-up of the warble analysis of Farabaugh et al. (1992), an automatic categorization program based on neural networks was developed and used to efficiently and reliably classify more than 25,000 warble elements from 4 budgerigars. The relative proportion of the resultant seven basic acoustic groups and one compound group is similar across individuals. Budgerigars showed higher discriminability of warble elements drawn from different acoustic categories and lower discriminability of warble elements drawn from the same category psychophysically, suggesting that they form seven perceptual categories corresponding to those established acoustically. Budgerigars also perceive individual voice characteristics in addition to the acoustic measures delineating categories. Acoustic analyses of long sequences of natural warble revealed that the elements were not randomly arranged and that warble has at least a 5th-order Markovian structure. Perceptual experiments provided convergent evidence that budgerigars are able to master a novel sequence between 4 and 7 elements in length. Through gradual training with chunking (about 5 elements), birds are able to master sequences up to 50 elements. The ability of budgerigars to detect inserted targets taken in a long, running background of natural warble sequences appears to be species-specific and related to the acoustic structure of warble sounds.
Cognitive and Motivational Parameters in Motivated Biases in Human Judgment
(2009) Chen, Xiaoyan; Kruglanski, Arie W.; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Motivational and cognitive factors can determine the extent and direction of information processing in judgment. When biasing motives are present, information can be distorted and judgment biased. The extent of this bias can be determined by the nature of the information, the relative magnitude of competing goals, and the individual's cognitive resources. Studies 1, 2 and 3 explored the effect of resource depletion on motivated distortions in judgment. Studies 4 and 5 examined the role of relative goal magnitude (of a biasing goal vs. a specific judgment goal) in the phenomena. I departed from the assumption that human knowledge is malleable, and that its alteration in a motivationally desirable direction may vary in difficulty across instances. It was assumed that overcoming the difficulty requires cognitive and/or motivational resources hence under certain circumstances resource-depletion should diminish individuals' ability to motivationally bias judgments. I also hypothesized when information is clear-cut (rather than ambiguous) making distortion difficult, a sufficient amount of biasing motivation could overcome the "reality constraints," holding the cognitive resources constant. In my first two studies participants' resources were depleted either via complex or simple presentational format of the information given (Study 1), or via engagement in a fatiguing prior activity (Study 2). In the third study (Study 3), I measured participants' stable cognitive capacity as a proxy for their available cognitive resources. All three studies provided supportive evidence for the hypothesis that motivated distortion is resource dependent. In Study 4 I manipulated the relative goal magnitude by experimentally increasing goal importance for either an academic success goal in line with the specific judgment task or a social wellbeing goal as the biasing goal. In Study 5 I altered relative goal magnitude through enhancing either a neutral goal or health concerns as the biasing goal. In both Study 4 and 5, orthogonal to the relative goal magnitude manipulation, stimulus ambiguity was made either high or low. Findings from Study 4 and 5 supported the hypothesis that sufficient magnitude of biasing goal could overcome distortion difficulty even in highly constraining circumstances.
BEYOND STATISTICAL LEARNING IN THE ACQUISITION OF PHRASE STRUCTURE
(2009) Takahashi, Eri; Lidz, Jeffrey; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The notion that children use statistical distributions present in the input to acquire various aspects of linguistic knowledge has received considerable recent attention. But the roles of learner's initial state have been largely ignored in those studies. What remains unclear is the nature of learner's contribution. At least two possibilities exist. One is that all that learners do is to collect and compile accurately predictive statistics from the data, and they do not have antecedently specified set of possible structures (Elman, et al. 1996; Tomasello 2000). On this view, outcome of the learning is solely based on the observed input distributions. A second possibility is that learners use statistics to identify particular abstract syntactic representations (Miller & Chomsky 1963; Pinker 1984; Yang 2006). On this view, children have predetermined linguistic knowledge on possible structures and the acquired representations have deductive consequences beyond what can be derived from the observed statistical distributions alone. This dissertation examines how the environment interacts with the structure of the learner, and proposes a linking between distributional approach and nativist approach to language acquisition. To investigate this more general question, we focus on how infants, adults and neural networks acquire the phrase structure of their target language. This dissertation presents seven experiments, which show that adults and infants can project their generalizations to novel structures, while the Simple Recurrent Network fails. Moreover, it will be shown that learners' generalizations go beyond the stimuli, but those generalizations are constrained in the same ways that natural languages are constrained. This is compatible with the view that statistical learning interacts with inherent representational system, but incompatible with the view that statistical learning is the sole mechanism by which the existence of phrase structure is discovered. This provides novel evidence that statistical learning interacts with innate constraints on possible representations, and that learners have a deductive power that goes beyond the input data. This suggests that statistical learning is used merely as a method for mapping the surface string to abstract representation, while innate knowledge specifies range of possible grammars and structures.
Caffeine Abstinence during the Menstrual Cycle: An Evaluation of Mood, Somatic, Cognitive, and Psychomotor Effects of Withdrawal
(2008) Vo, Hoa Thi; Smith, Barry D; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The purpose of the present study was to extend our understanding of caffeine withdrawal symptoms and of potentially differing symptom patterns across phases of the menstrual cycle. Forty-eight moderate habitual caffeine consumers, age 18 to 25 years, were recruited from the University of Maryland. Exclusion criteria included current or past psychiatric conditions (within six months) and premenstrual syndrome (PMS). In addition to daily diaries (including the caffeine intake survey, premenstrual syndrome questionnaires, LH surge test, and the caffeine withdrawal checklist), the effect of caffeine abstinence on psychomotor tasks was assessed during the follicular (around day 5 of the cycle) and luteal phases (approximately 4 days after the LH surge) of the menstrual cycle. Data analyses focused on withdrawal symptom ratings and psychomotor performance one day during the follicular phase and one day during the luteal phase of the cycle after 24 hours of caffeine abstinence. A series of repeated measures ANOVAs were used to assess caffeine withdrawal effects and differences in these effects between the follicular and luteal phases. Results confirmed the presence of certain withdrawal symptoms, but did not provide support for phase-differentiated effects of self-reported withdrawal symptoms or of psychomotor and cognitive performance differentials across the menstrual cycle. However, withdrawal, as a result of caffeine abstinence, did impact self-report symptom ratings during select days of abstinence, as compared with days of non-abstinence, during the both the follicular and the luteal phase. The present study is the first multi-method study to examine the effects of caffeine abstinence on habitual consumers across the menstrual cycle.
HEAD-EYE COORDINATION DURING A NATURAL TAPPING TASK
(2009) Herst, Andrew Neal; Dougherty, Michael R; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This thesis describes the research of Herst et al. (2001) who examined the coordination of head and eye movements while participants searched for targets under natural conditions in which the head was free to move. This investigation was done because, while the technical difficulties in measuring these patterns of head-eye coordination in humans have been overcome, the results obtained over the last 35 years have yet to show what the typical pattern of head-eye coordination looks like. Herst et al. (2001) described the `natural' temporal coordination of head and eye of four participants who tapped a sequence of targets arranged in 3D on a worktable in front of them. The results were not expected based on prior studies of head-eye coordination performed under less natural conditions. This thesis reinterprets the original (2001) findings and draws new conclusions in the light of new research on head-eye coordination conducted since then.
THE EFFECT OF GOAL DISTANCE ON GOAL VALUE AND ESCALATION OF COMMITMENT
(2009) Ting, Hsuchi; Wallsten, Thomas S; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Escalation of commitment describes individuals' tendencies to persist in a chosen course of action. The traditional account of escalation of commitment assumes that sunk cost is the primary antecedent for this behavior. However, it has been noted that high sunk costs are confounded with progress made toward a goal and hidden payoff information. Thus, the apparent escalation tendency may be a consequence of goal proximity and information search rather than of sunk costs. Experiments 1 and 2 show that individuals' tendencies to escalate reflect the classical goal-gradient effect after controlling for the sunk costs. Moreover, Experiment 1 also shows that controlling for progress toward the goal, increased sunk costs decreases escalation. In addition, Experiment 2 shows that individuals attribute more value to the goal as they get closer to it, thus providing an alternative explanation for escalation of commitment. Experiments 3a and 3b demonstrate that individuals committed to a course also devalue other course of actions not chosen. These results suggest a new interpretation for escalation of commitment and new approaches to guiding people to avoid it.
The predictive nature of language comprehension
(2009) Lau, Ellen Frances; Phillips, Colin; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
This dissertation explores the hypothesis that predictive processing--the access and construction of internal representations in advance of the external input that supports them--plays a central role in language comprehension. Linguistic input is frequently noisy, variable, and rapid, but it is also subject to numerous constraints. Predictive processing could be a particularly useful approach in language comprehension, as predictions based on the constraints imposed by the prior context could allow computation to be speeded and noisy input to be disambiguated. Decades of previous research have demonstrated that the broader sentence context has an effect on how new input is processed, but less progress has been made in determining the mechanisms underlying such contextual effects. This dissertation is aimed at advancing this second goal, by using both behavioral and neurophysiological methods to motivate predictive or top-down interpretations of contextual effects and to test particular hypotheses about the nature of the predictive mechanisms in question. The first part of the dissertation focuses on the lexical-semantic predictions made possible by word and sentence contexts. MEG and fMRI experiments, in conjunction with a meta-analysis of the previous neuroimaging literature, support the claim that an ERP effect classically observed in response to contextual manipulations--the N400 effect--reflects facilitation in processing due to lexical-semantic predictions, and that these predictions are realized at least in part through top-down changes in activity in left posterior middle temporal cortex, the cortical region thought to represent lexical-semantic information in long-term memory,. The second part of the dissertation focuses on syntactic predictions. ERP and reaction time data suggest that the syntactic requirements of the prior context impacts processing of the current input very early, and that predicting the syntactic position in which the requirements can be fulfilled may allow the processor to avoid a retrieval mechanism that is prone to similarity-based interference errors. In sum, the results described here are consistent with the hypothesis that a significant amount of language comprehension takes place in advance of the external input, and suggest future avenues of investigation towards understanding the mechanisms that make this possible.
Form, meaning and context in lexical access: MEG and behavioral evidence
(2009) Almeida, Diogo; Poeppel, David; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
One of the main challenges in the study of cognition is how to connect brain activity to cognitive processes. In the domain of language, this requires coordination between two different lines of research: theoretical models of linguistic knowledge and language processing on the one side and brain sciences on the other. The work reported in this dissertation attempts to link these two lines of research by focusing on one particular aspect of linguistic processing, namely lexical access. The rationale for this focus is that access to the lexicon is a mandatory step in any theory of linguistic computation, and therefore findings about lexical access procedures have consequences for language processing models in general. Moreover, in the domain of brain electrophysiology, past research on event-related brain potentials (ERPs) - electrophysiological responses taken to reflect processing of certain specific kinds of stimuli or specific cognitive processes - has uncovered different ERPs that have been connected to linguistic stimuli and processes. One particular ERP, peaking at around 400 ms post-stimulus onset (N400) has been linked to lexico-semantic processing, but its precise functional interpretation remains controversial: The N400 has been proposed to reflect lexical access procedures as well as higher order semantic/pragmatic processing. In a series of three MEG experiments, we show that access to the lexicon from print occurs much earlier than previously thought, at around 200 ms, but more research is needed before the same conclusion can be reached about lexical access based on auditory or sign language input. The cognitive activity indexed by the N400 and its MEG analogue is argued to constitute predictive processing that integrates information from linguistic and non-linguistic sources at a later, post-lexical stage.
Social Exclusion and the Choice of Important Groups
(2009) Fishman, Shira; Kruglanski, Arie W.; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Social connections are fundamental to our existence. As a result, social exclusion is a painful and distressing experience. When belonging is thwarted, people seek inclusion which can be achieved through group membership. Thus, excluded individuals and/or those whose need to belong is particularly strong will be particularly motivated to join groups. Moreover, to the extent that the need to belong is satisfied by closeness with other group members, and closeness is a feature of group cohesion, excluded individuals or ones with a strong need to belong are likely to be attracted to highly cohesive groups. Finally, the subjective importance of a group to its members should determine the degree of perceived cohesion. Importance of a group is defined as the group's centrality to individuals' social identity. The more central a given dimension is to one's identity, the greater the attraction to individuals sharing that dimension (Byrne, 1961). Hence, the more important the group, the greater the attraction of the members to each other, defining group cohesion. Ultimately then, the greater the individuals' prior experience of exclusion or the greater their need to belong, the greater their motivation should be to join important (vs. less important) groups. These notions are investigated in the present dissertation. A review of the literature on social exclusion and the similarity-attraction hypothesis is presented followed by two studies showing that, both in the lab and in the real world, individuals who have been socially excluded want to join and/or feel more connected to important groups.

Theses and Dissertations from UMD

Browse

Filters

Settings

Sort By

Results per page

Search Results