Three-dimensional kinematic analysis was used to precisely quantify alterations in gait and compensatory behaviors in rat performance on beamwalk and treadmill tasks following moderate traumatic brain injury. Measures included limb height, joint angles, adduction, flexion, and swing/stance phase duration. Injury-associated changes on the treadmill included postural and hip angle change, and increases in hip height and adduction. The beamwalk presented as a more sensitive measure when coupled with kinematic analysis, as differences between injury groups were evident on measures including knee, ankle, elbow, and mid hip height. Animal response was diverse, possibly reflecting individual compensatory strategies which varied among injured animals. Kinematic analysis was ultimately shown to be a useful tool in characterizing and dissociating initial impairment, compensation, and recovery.

The general aim of this thesis was to examine variations in the word decoding skills of reading disabled children. These variations were related to possible cognitive, developmental, and environmental causes of reading disability. Possible implications for educational interventions were also analysed. The thesis critically examines the inclusion of the concept of intelligence in the definition of developmental dyslexia. It is suggested that variations in word decoding skills should offer a more solid basis for a study of varieties of reading disability. The empirical studies showed that a) in young children there was a shift from phonological to orthographic word decoding; b) phonological type children (weak in phonological decoding) were characterised by specific phonological deficits; c) surface type children (weak in orthographic decoding) showed more global cognitive deficits suggesting a general developmental delay; d) surface type children showed impaired visual implicit memory for words, which might be associated with limited print exposure; e) an improvement in phonological awareness only transferred to an improved text reading ability for some reading disabled children; f) children who did not benefit from a phonological intervention seemed to rely on orthographic word decoding in text reading. Thus, the thesis suggests that variations in phonological and orthographic word decoding skills offer a useful basis for the study of varieties of reading disability and that educational interventions should pay regard to what the child is already attempting to do when reading. / On the day of the defence date the status of article IV was: Manuscript.

Previous research has indicated that meaningful background speech affects individuals reading comprehension performance differently and that this difference is related to working memory capacity. But what mechanism in working memory that is involved is not well understood. The present study’s main purpose was to investigate if individual differences in susceptibility to effects of speech on reading comprehension are moderated by working memory capacity as measured by the number updating task and two different mechanisms within this construct; delayed suppression (i.e. the inhibition of information that once was task-relevant but no longer is) and immediate suppression (i.e. the inhibition of processed but irrelevant information, while withholding attention focused on the to-be-recalled task-relevant items). Forty participants performed a number updating task and a reading comprehension task in silence and with meaningful background speech. The results indicated that the immediate suppression mechanism moderates the effects of background speech on reading comprehension. Those who can’t handle the interference from the background speech let the task-irrelevant information interfere with the ongoing cognitive task and therefore are more likely to be distracted by the background speech while reading a text.

Executive control allows us to ignore distraction and switch between tasks in a flexible, yet organized fashion. While a hallmark of controlled behavior, distinctions among executive control processes are not thoroughly agreed upon. The present work explored the organization of two of these executive control processes, inhibition and shifting, and their relationship to each other. There were two primary goals. The first goal was to investigate the distinction among inhibitory control processes, as “inhibition” has oftentimes been considered a unitary construct. For example, there is evidence that response-distractor inhibition, which involves resolving interference from dominant responses or distractors in the external environment, is different from resistance to proactive interference (PI), which involves overcoming interference from previously relevant representations in memory. Using aging, neuropsychology, and individual differences methodologies, I investigated the unity and diversity of inhibitory control mechanisms. The healthy aging and neuropsychological evidence supported a distinction between response-distractor inhibition and resistance to proactive interference. However, when controlling for processing speed, the individual differences work suggested a need for further specification, as only a subset of these tasks emerged in the single factor model that provided the best fit to the data. The second goal was to explore how inhibitory control processes interact with task switching, as some theoretical accounts of task switching have suggested that switch costs result from the need to overcome interference from the previously relevant task. Inconsistent with these theories, I found little relation between inhibitory control and measures of global and local task switching, and instead, working memory served as the best predictor of these shifting measures. In contrast, inhibitory control was related to the backward inhibition abilities of older adults. These findings are discussed within a theory of working memory that accounts for the patterns of results found across the different methodologies.

Executive control allows us to ignore distraction and switch between tasks in a flexible, yet organized fashion. While a hallmark of controlled behavior, distinctions among executive control processes are not thoroughly agreed upon. The present work explored the organization of two of these executive control processes, inhibition and shifting, and their relationship to each other. There were two primary goals. The first goal was to investigate the distinction among inhibitory control processes, as “inhibition” has oftentimes been considered a unitary construct. For example, there is evidence that response-distractor inhibition, which involves resolving interference from dominant responses or distractors in the external environment, is different from resistance to proactive interference (PI), which involves overcoming interference from previously relevant representations in memory. Using aging, neuropsychology, and individual differences methodologies, I investigated the unity and diversity of inhibitory control mechanisms. The healthy aging and neuropsychological evidence supported a distinction between response-distractor inhibition and resistance to proactive interference. However, when controlling for processing speed, the individual differences work suggested a need for further specification, as only a subset of these tasks emerged in the single factor model that provided the best fit to the data. The second goal was to explore how inhibitory control processes interact with task switching, as some theoretical accounts of task switching have suggested that switch costs result from the need to overcome interference from the previously relevant task. Inconsistent with these theories, I found little relation between inhibitory control and measures of global and local task switching, and instead, working memory served as the best predictor of these shifting measures. In contrast, inhibitory control was related to the backward inhibition abilities of older adults. These findings are discussed within a theory of working memory that accounts for the patterns of results found across the different methodologies.

This study explored external and internal factors and their effect on childrens memory of a naturalistic, potentially stressful event, namely, a dental procedure. Specifically, question format (yes/no questions versus multiple choice questions) and temporal delay (short delay versus long delay) were the external factors examined, while anxiety, temperament, distress level, working memory and previous experience were the internal factors examined. Children (N=68) aged 4-12 years and their parents participated. Prior to the procedure, children provided ratings of their current anxiety on an anxiety rating scale. Following the procedure, children provided pain ratings and were given 24 forced choice questions regarding the dental event. Parents responded to questions regarding their childs previous dental experiences and temperament via a questionnaire. The findings suggest that: (a) multiple-choice questions are more problematic than yes/no questions, (b) that younger children are more suggestible than older children, especially when asked no and absent feature questions; (c) children who report more pain and anxiety, and whose parents describe them as less sociable, evidence higher rates of suggestibility; and (d) after a two month delay, on average, children accurately recalled their pain for the dental event, however, higher trait anxiety scores were associated with higher recollection of experienced pain. The findings are discussed with respect to implications for interviewing children and for management of pain in clinical settings.

This study explored external and internal factors and their effect on childrens memory of a naturalistic, potentially stressful event, namely, a dental procedure. Specifically, question format (yes/no questions versus multiple choice questions) and temporal delay (short delay versus long delay) were the external factors examined, while anxiety, temperament, distress level, working memory and previous experience were the internal factors examined. Children (N=68) aged 4-12 years and their parents participated. Prior to the procedure, children provided ratings of their current anxiety on an anxiety rating scale. Following the procedure, children provided pain ratings and were given 24 forced choice questions regarding the dental event. Parents responded to questions regarding their childs previous dental experiences and temperament via a questionnaire. The findings suggest that: (a) multiple-choice questions are more problematic than yes/no questions, (b) that younger children are more suggestible than older children, especially when asked no and absent feature questions; (c) children who report more pain and anxiety, and whose parents describe them as less sociable, evidence higher rates of suggestibility; and (d) after a two month delay, on average, children accurately recalled their pain for the dental event, however, higher trait anxiety scores were associated with higher recollection of experienced pain. The findings are discussed with respect to implications for interviewing children and for management of pain in clinical settings.

The belief bias effect – the finding that prior beliefs influence judgments of logic and evidence – has been a topic of much empirical investigation in both deductive and causal reasoning. However, to date, no research has examined the degree to which such biases are the result of common or distinct mechanisms in these two domains. By using common scales of measurement, I examine the degree to which individuals show common biases in these two domains in two experiments. Surprisingly, although the belief bias effect was observed in both paradigms, biases in one domain were unreliably associated with biases in the other domain. Experiment 2 included 6 measures of individual differences in an attempt to uncover the observation of differential biases in these domains. Dogmatism was found to be the single most predictive measure of belief bias, but only in deductive reasoning. These data are discussed in terms of dual process theories of reasoning.

The belief bias effect – the finding that prior beliefs influence judgments of logic and evidence – has been a topic of much empirical investigation in both deductive and causal reasoning. However, to date, no research has examined the degree to which such biases are the result of common or distinct mechanisms in these two domains. By using common scales of measurement, I examine the degree to which individuals show common biases in these two domains in two experiments. Surprisingly, although the belief bias effect was observed in both paradigms, biases in one domain were unreliably associated with biases in the other domain. Experiment 2 included 6 measures of individual differences in an attempt to uncover the observation of differential biases in these domains. Dogmatism was found to be the single most predictive measure of belief bias, but only in deductive reasoning. These data are discussed in terms of dual process theories of reasoning.

Our laboratory has previously shown that exposure to social disruption (SDR) the week prior to Theiler’s murine encephalomyelitis virus (TMEV) infection exacerbates disease course, resulting in increased infection-related sickness behaviors, motor impairment, CNS viral titers, and CNS inflammation. These adverse effects of SDR were prevented by ICV infusion of a neutralizing antibody to IL-6 during the stress exposure period. These findings suggest that stress-induced increases in IL-6 are necessary to exacerbate acute TMEV infection, but the exact mechanism remains unknown. This thesis tested the hypotheses that SDR up-regulates central cytokine expression, exacerbates TMEV infection through cross-sensitization of virus-induced cytokine expression, and that social rank modulates the effect of SDR. In Experiment 1, Balb/cJ mice underwent the 0, 1, or 6 SDR sessions and were then sacrificed 0, 2, or 12 hours post SDR. Experiment 2 subjects received ICV infusions of either IL-6 neutralizing antibody or its vehicle before each of six 2 h SDR sessions or the control condition, the week prior to infection. In Experiment 3 mice were tested for pre-existing social rank prior to SDR and infection. Results indicate that (1) SDR increases virus-induced IL-6, IL-1B, and CD11b mRNA expression in brain,that these SDR-induced increases and acute TMEV exacerbation are prevented by ICV infusion of the IL-6 neutralizing antibody during the stress exposure period, and that (2) social rank does not modulate affects of SDR but baseline anxiety does. These findings suggest that SDR exacerbates acute TMEV infection through cross-sensitization of virus-induced cytokine expression and that baseline anxiety is a significant modulator of SDR.