Rural inhabitants of developing countries face extraordinarily risky environments, and decision-making under risk has crucial implications for the welfare of the rural poor. Therefore, obtaining a better understanding of the behaviour under risk of low-income populations is a vital step in the comprehension of human behaviour, and is important for effective policy design and evaluation, as well as for shedding light on production, investment and technology adoption decisions. In Chapter One, I analyze data collected from a laboratory experiment involving poor subjects in rural Ethiopia, in order to determine which decision models (and corresponding risk preferences) best describe the decision-making under risk of inhabitants. I find that expected utility theory (EUT) does not provide a good overall description of the decisions made by participants in the experiment; instead, there is evidence of probability weighting and loss aversion, implying that rank-dependent and reference-dependent choice models are more likely to represent the true latent decision-making process of subjects. In Chapter Two, I analyze combined experimental and survey data from rural Ethiopia in order to evaluate the determinants of risk preferences as well as assess the degree of asset integration in experimental decisions. Analyzing both EUT and non-EUT decision models and using an instrumental variable strategy, I find that household wealth negatively affects both risk aversion and loss aversion, but independent background risk has no effect on risk preferences. Further, I find evidence of narrow framing, as opposed to asset integration, suggesting that participants make decisions in the experiment in isolation from outside wealth. In Chapter Three, I analyze experimental data from Brazil to evaluate whether subjects understand decision problems that use the complex Multiple Price List (MPL) elicitation procedure, and to determine which decision models best describe observed choices. I find that the MPL decision problems of the experiment enable a finer characterization of risk preferences as compared to Ordered Lottery Selection problems (used in the Ethiopian experiment). However, I find that a significant fraction of choice patterns in the MPL problems are intransitive, and the evidence indicates that subjects did not properly understand the decision problems and thus observed choices do not reveal true risk preferences. Therefore, the relatively complex MPL procedure may not be suitable for experiments conducted with poorly-educated subjects in developing country settings. Chapter Four presents a theory outlining the relationship between rational demand for index insurance – for which the net transfer between insurer and policyholders depends only on a publicly verifiable index – and wealth. Further, the validity of this theory is tested using the experimental data from Ethiopia. In line with the theoretical model presented, due to basis risk and actuarially unfair premiums, demand for index insurance is hump-shaped – first increasing then decreasing – in wealth. The results indicate that the low take-up of this product observed among the poorest (and most risk averse) individuals in recent field studies may result from rational choice rather than credit constraints or poor decision-making.

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Despite the burgeoning literature documenting the effects of breast-feeding on cognition and educational attainment over the past several decades, there remains important gaps in our knowledge regarding whether this relationship is dictated by sociodemographic factors. The current investigations, which examined the literature on the effects of breast-feeding on cognition and educational attainment in children, adolescents, and older adults addressed these gaps. Chapter 2 was an up-to-date global systematic review of population studies in individuals ≤ 25 years and ≥ 25 years of age. Results indicate that the majority of published studies conducted by researchers demonstrated a positive relationship between the effect of breast-feeding on cognitive outcomes and educational attainment. Additionally, findings highlighted the importance of possible confounders and how adjusting for them can change the relationship between breast-feeding and cognition and educational attainment. Chapter 3 investigated the breast-feeding-cognition/educational attainment relationship across race, as well as whether mother-child stimulation might mediate this relationship. The National Longitudinal Study of Adolescent to Adult Health (Add Health) was used to examine the effect of being breast-fed or not, and duration on cognitive outcomes and grade point average (GPA). Results indicate that individuals who were breast-fed had slightly higher GPAs and performance on both a vocabulary test and a number recall test compared to adolescents who were not breast-fed. There was an effect for race, but no interaction between race and breast-feeding. Mother-child stimulation had a limited effect on the relationship between breast-feeding and cognitive outcomes and GPA. Chapter 4 explored whether the effect observed in adolescence persists into older adulthood. The Reasons for Geographic and Racial Differences in Stroke (REGARDS) Cohort was used to examine this relationship in adults age ≥ 45 years. The covariates included sex of adolescent, race (Black or White), maternal education, paternal education, maternal smoking history, number of other children mother has, resident location (urban/not-urban), and a financial adversity index. This was a composite score consisting of yes or no responses to (1) do you have health insurance, (2) have you been employed within the past 12 months, (3) are you on public assistance, and (4) do you have enough money to pay your bills? Results show that self-report history of being breast-fed did not current predict performance on cognitive tests. Additionally, neither race nor sex moderated this relationship between breast-feeding and cognition. Overall, evidence from the review and two studies highlight the important of assessing the effect of breast-feeding on cognition and educational attainment in populations with varying confounding factors, however, while some of the results are inconsistent with our hypothesis, replication is clearly essential to further explore the possible underlying mechanism.

Visual working memory (WM) is the ability to hold information in mind for a short time before acting on it. The capacity of WM is strikingly limited. To make the most of this precious resource, humans exhibit a high degree of cognitive flexibility: We can prioritize information that is relevant to behavior, and inhibit unnecessary distractions. This thesis examines some behavioral and neural correlates of flexibility in WM. When information is of particular importance, anticipatory attention can be directed to where it will likely appear. Oscillations in visual cortex, in the 10-Hz range, play an important role in regulating excitability of such prioritized locations. Chapter 4 describes how even spontaneous fluctuations in 10-Hz synchronization (measured by electroencephalography, EEG) before encoding influence WM. Chapters 2 and 3 describe how attention can be directed retrospectively to items even if they are already stored in WM. Chapter 3 discusses how retrospective cues change neural synchronization similarly to anticipatory cues. Behavioral and neural measures additionally indicate that the boosting of an item through retrospective cues does not require prolonged deployment of attention: rather, it may be a transient process. The second half of this thesis additionally examines how items are represented in visual WM. Chapter 5 summarizes a study using pattern analysis of magnetoencephalographic (MEG) and EEG data to decode features of visual templates stored in WM. Decoding appears transiently around the time when potential target stimuli are expected, in line with a flexible reactivation mechanism. Chapter 6 further examines separate cortical networks involved in protecting vs. updating items in WM, and tests whether task relevance changes how well WM contents can be decoded. Finally, Chapter 7 summarizes the thesis and discusses how attentional flexibility can merge WM with a wider range of sources of behavioral control.

Distraction during driving is one of the leading contributors to injury and mortality rates in traffic accidents. The aim of this current thesis was to consider 1) whether oculomotor and electrophysiological metrics could act as markers of cognitive distraction; 2) whether decrements in hazard perception performance caused by secondary cognitive task demand are to some extent due to cognitive load interfering with processes of alerting, orienting, inhibitory control and visual search; 3) what elements of secondary cognitive tasks have the greatest impact on hazard perception performance; and 4) whether the susceptibility of previously identified markers of cognitive distraction are affected by primary task difficulty. Over the course of four Experiments we recorded the effects of secondary cognitive task demand on behavioural, oculomotor and electrophysiological metrics during a variety of low-level and complex visual tasks. Taken together the experiments of this thesis have demonstrated that secondary cognitive task demand interferes with not just one but every component process of hazard perception performance that was examined. Next, this research has demonstrated that measures such as blink rates, saccade peak velocities, the spread of fixations along the horizontal axis as well as reductions in alpha and beta power output may be reliable indicators of secondary cognitive task demand regardless of the type of primary task. Finally we have shown that the co-registration of eye movements, EEG and ERP measures is a viable method with which to study the cognitive processes involved in visual processing within low level and complex visual tasks.

According to the perception-action perspective of development, human tool use is the result of object-to-surface affordance discovery subsequent to self-guided object and surface explorations (Gibson & Pick; Lockman, 2000; Siegler, 1996; Smitsman, 1997). However, because tools are often made with a specific purpose, learning to use them is also largely influenced by culture, suggesting that social learning is as valuable to meaningful affordance discovery as teaching oneself (Tomasello, 1999). In line with the perception-action view, with the attainment of greater physical and cognitive capability, infants are expected to better approximate and better understand the value of imitating the actions of others. Because meaningful tool use emerges around the start of the second year, the current study investigated how 14- and 18-month-old Chinese and American infants differ in their exploration strategy, whether self- or other-guided, when presented with a simple tool use task. The findings suggest that important developmental gains are made between 14 and 18 months of age, particularly in social-cognition, as older infants are more likely to imitate an adult demonstration compared to younger infants / acase@tulane.edu

This study addressed the effects of background music on preschool children during block play. Music was manipulated to examine its observed effects on children's movement and dramatic play, as well as on the occurrence of group play. The tempo in the background music was manipulated to produce equal and counterbalanced days of slow, fast, and no background music While significant differences in the active/quiet qualities of play themes relative to music conditions were expected, no differences were noted. This is possibly due to the low frequency of identifiable play themes and to the redundancy of themes that were identified. It was noted, however, that the emergence of active versus quiet themes coincided with the tempo of music on the day the theme emerged. (Abstract shortened with permission of author.) / acase@tulane.edu

Some studies of stroke patients with semantic deficits have found no effect of word frequency on semantic tasks, as well as inconsistent performance across items and tasks. A deficit in semantic control has been suggested as the source of the deficit - i.e., an inability to focus on semantic features appropriate to the task. In the present study, two stroke patients performed significantly better in single-distractor versions (low semantic control) than multiple-distractor versions of semantic tasks (high semantic control) of comprehension tasks, which appears consistent with the semantic control hypothesis. On the other hand, two aphasic patients showed substantially better performance for auditory than visual presentation of words in comprehension tasks – a finding that is not expected on the basis of semantic control. Experiment 1 evaluated whether performance on a multiple-distractor comprehension task could be predicted solely on the basis of performance on a single-distractor version using Luce’s choice axiom. Single distractor performance significantly predicted performance and no convincing evidence was obtained for a role for semantic control. Experiment 2, which examined the modality effect, showed that for one of the patients, worse performance with auditory presentation was most likely due to rapid decay of phonological representations. For the other, worse performance was most likely due to a disruption to phonological representations of words or to their connection to semantic representations. In all, the results suggest that word comprehension deficits in aphasia can result from a variety of sources and not all are due to semantic control deficits.

<p>Recent studies have linked expressive suppression to impairments in interpersonal functioning, but the mechanism underlying this relationship has not been well articulated. One possibility is that the individual who engages in expressive suppression is impaired in perceiving the emotions of others, a critical ability in successful interpersonal functioning. In the current study, participants were presented with a series of photographs of facial expressions that were manipulated so that they appeared to "morph" from neutral into full emotion expressions. As they viewed these images, participants were instructed to identify the expression as quickly as possible, by selecting one of the six emotion labels (happiness, sadness, fear, anger, surprise, and disgust) on the screen. Prior to this task, participants were randomized to one of three groups: instructed to mimic the expressions on the screen, instructed to suppress all emotion expressions, or not given specific instructions on how to control expressions (the control group). The speed with which participants accurately identified emotional expressions (emotion sensitivity) was the primary variable of interest. Overall, participants in the suppression condition were found to be slower to accurately identify emotions, while no statistically-significant differences were found between the mimicry and no-instructions conditions. The decreased emotion sensitivity in the suppression group could not be accounted for by impulsive responding, decreased sensitivity at full expression, or perceived difficulty of task.</p> / Dissertation

<p>Altered dietary availability of the vital nutrient choline during early development leads to persistent changes in brain and behavior throughout adulthood. Prenatal choline supplementation during embryonic days (ED) 12-17 of the rodent gestation period enhances memory capacity and precision and hippocampal plasticity in adulthood, and protects against spatial learning and memory deficits shortly after excitotoxic seizures, whereas prenatal choline deficiency can compromise hippocampal memory and plasticity in adulthood. Recent evidence from our laboratory has determined that lifelong proliferation of newborn neurons in the adult hippocampus, a feature of adult hippocampal plasticity that has been implicated in some aspects of learning and memory, is modulated by early choline availability. Prenatal choline's effects on adult neurogenesis may be one mechanism for diet-induced cognitive changes throughout life and in response to injury, although little is known about the mechanisms underlying how prenatal choline alters adult neurogenesis or the neural mechanisms underlying prenatal choline supplementation's protection against cognitive deficits after seizures. To address these issues, the present set of experiments investigated how prenatal choline availability modulates specific properties of neurogenesis in the adult brain (in the intact brain and in response to injury), as well as hippocampal markers known to change in response to excitotoxin-induced seizures, and sought to relate changes in neurogenesis and in neuropathological markers following injury to changes in performance on spatial learning and memory tasks. Subjects in each experiment were adult offspring from rat dams that received either a control diet or diet supplemented with choline chloride or deficient of choline on ED 12-17. To measure neurogenesis, rats were given injections of the mitotic marker bromodeoxyurdine to label dividing cells in the hippocampus. Prenatal choline supplementation enhanced several properties of basal adult hippocampal neurogenesis (cell division and survival, neural stem/progenitor cell phenotype and proliferative capacity, trophic support), and this increase was associated with improvements in spatial working memory retention in a delayed-matching-to-place water maze task. In contrast, prenatal choline deficiency had little effect on basal adult hippocampal neurogenesis, and no effect on spatial memory performance. Prenatal choline supplementation also enhanced olfactory bulb neurogenesis without altering cell proliferation in the subventricular zone, while prenatal choline deficiency had no effect on either measure, showing for the first time that prenatal choline's effects on adult neurogenesis is similarly expressed in another distinct neurogenic region of the adult brain. Altered prenatal choline availability also modulated the hippocampal response to kainic acid-induced seizures where supplementation attenuated while deficiency had no effect on the injury-induced proliferative response of the dentate gyrus shortly after injury. Prenatal choline supplementation also attenuated other markers of hippocampal neuropathology shortly after seizures and promoted the long-term hippocampal recovery from seizures months after injury, including rescuing declines in adult hippocampal neurogenesis and in spatial memory performance in a standard water maze task. Taken together, these findings demonstrate a robust neuroprotective effect of prenatal choline supplementation that may be driven by enhanced adult hippocampal plasticity and trophic support prior to injury, and shed light on the mechanisms underlying how prenatal choline availability alters adult hippocampal neurogenesis, which may contribute to changes in memory capacity and precision both throughout life and following neural assault.</p> / Dissertation