UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Information Uncertainty Influences Learning Strategy from Sequentially Delayed Rewards(2023) Maulhardt, Sean Richard; Charpentier, Caroline; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The problem of temporal credit assignment has long been posed as a nontrivial obstacle to identifying signal from data. However, human solutions in complex environments, involving repeated and intervening decisions, as well as uncertainty in reward timing, remain elusive. To this end, our task manipulated uncertainty via the amount of information given in their feedback stage. Using computational modeling, two learning strategies were developed that differentiated participants’ updates of sequentially delayed rewards: eligibility trace whereby previously selected actions are updated as a function of the temporal sequence - and tabular update - whereby additional feedback information is used to only update systematically-related rather than randomly related past actions. In both models, values were discounted over time with an exponential decay. We hypothesized that higher uncertainty would be associated with (i) a switch from tabular to eligibility strategy and (ii) higher rates of discounting. Participants’ data (N = 142) confirmed our first hypothesis, additionally revealing an effect of the starting condition. However, our discounting hypothesis had only weak evidence of an effect and remains an open question for future studies. We explore potential explanations for these effects and possibilities of future directions, models, and designs.Item Development of Motivational Influences on Monitoring and Control Recruitment in the Context of Proactive and Reactive Control in Adolescent Males(2020) Bowers, Maureen; Fox, Nathan A; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Adolescence and the onset of puberty is a time period of physiological and behavioral changes that include a heightened reward sensitivity, but underdeveloped cognitive control. Cognitive control involves monitoring for salient stimuli and recruiting control to adapt behavior advantageously to reach a specific goal and is supported by the three domains of executive functioning (EF): inhibitory control, set-shifting, and working memory. Proactive control is engaged after an informative cue in preparation for an upcoming stimulus, while reactive control can be employed when preparation is not possible and you need to respond to a stimulus. Oscillations in the theta frequency (4-8Hz) during both cue presentation and stimulus presentation are implicated in proactive and reactive control processes. While reward has been shown to upregulate proactive control in adults, little work has assessed how reward influences theta oscillations during both proactive and reactive control throughout adolescence and pubertal development. Further, no work has sought to understand how EF abilities bolster reward-related changes in proactive or reactive control. Here, 68 adolescent males (Meanage=13.61, SDage=2.52) aged 9 – 17 years old completed a rewarded cued flanker paradigm while electroencephalogram (EEG) was collected. They also completed tasks from the NIH toolbox that tap the three EF domains. Behaviorally, reward hindered performance on proactive trials, particularly in mid-puberty, while enhancing performance on reactive trials. Reward was associated with increases in cue-locked theta power, but with overall reductions in cue-locked theta ICPS. Stim-locked theta power increased on reactive trials with increasing age, while stim-locked theta ICPS peaked in mid-adolescence for rewarded trials. Increased cue theta power was associated with worse performance on proactive trials. On proactive trials, adolescents with low levels of inhibitory control experience more reward-related interference, while reward-related interference was mitigated by better set-shifting abilities only in younger and older adolescents. In conclusion, reward differentially impacts proactive and reactive control throughout adolescent development and EF influences the impact of reward on proactive control throughout adolescence.Item Motivation and Effort in Individuals with Social Anhedonia(2012) McCarthy, Julie; Blanchard, Jack J; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The current study sought to better understand differences in motivation and effort in individuals with social anhedonia. Social anhedonia is a core negative symptom and one of the strongest predictors for the development of schizophrenia-spectrum disorders. Because current research examining motivation and effort deficits has focused on self-report questionnaires and behavioral tasks, little is known about possible underlying mechanisms of social anhedonia. Thus, the current study examined effortful decision making (monetary reward task) and physiological measures of effort mobilization (cardiovascular reactivity) and investigated whether findings were specific to social anhedonia or were shared with positive symptoms of schizophrenia spectrum disorders (e.g., perceptual aberrations and magical ideation, together referred to as `PerMag') and healthy controls. Results indicated that elevated social anhedonia was related to more effortful decision making in the context of uncertain probability of reward, but there were no group differences with respect to physiological measures of effort.