O sinal de entrada na retina é decomposto em termos de frequência espacial (FE), variações periódicas de luminância ao longo do espaço. Existe vasta literatura sobre o processamento de FE no córtex visual primário. No entanto, não se sabe ao certo como esta informação sensorial básica é processada e integrada numa visão de alto nível. Esta tese aborda este tema ao investigar lateralidade cerebral, tempo de processamento e contexto cognitivo em três diferentes seções com objetivos específicos. Estas seções investigaram comportamentalmente visão de alto nível tendo a face humana como estímulo, dado sua relevância biológica e social. Na primeira seção (Theoretical Review), uma revisão apresenta estudos clínicos e neuropsicológicos que mostram áreas cerebrais envolvidas na percepção de faces e como os hemisférios esquerdo e direito realizam um processamento holístico e analítico baseado em informações de FEs. A especialização hemisférica de FE no reconhecimento de faces é então revisada e discutida. Concluiu-se que assimetrias sensoriais podem ser a base para assimetrias cognitivas de alta ordem. Ademais, foi destacado a influência do tempo de processamento. Na segunda seção (Study 1), foi investigado por método psicofísico a lateralidade de baixas e altas FEs no reconhecimento de faces em diferentes tempos de exposição. Faces com filtragem de FE foram apresentadas em campo visual dividido em alta e baixa restrição temporal em duas tarefas: reconhecimento facial (Experimento 1) e reconhecimento do sexo facial (Experimento 2). No Experimento 1, informações faciais de baixas e altas FEs foram mais eficientemente processadas no hemisfério direito e esquerdo, respectivamente, sem efeito do tempo de exposição das faces. Os resultados do Experimento 2 mostraram uma assimetria do hemisfério direito para baixas FEs em baixa restrição temporal. Conclui-se que o processamento de altas e baixas FEs é lateralizado nos hemisférios cerebrais no reconhecimento de faces. No entanto, a contribuição de altas e baixas FEs é dependente da tarefa e do tempo de exposição. Na terceira seção (Study 2) foi investigado qual estratégia temporal, coarse-to-fine (de baixas para altas FEs) ou fine-to-coarse, cada hemisfério cerebral utiliza para integrar informação de FE de faces humanas numa tarefa de categorização facial homem-mulher. Sequências dinâmicas breves coarse-to-fine e fine-to-coarse de faces foram apresentadas no campo visual esquerdo, direito e central. Os resultados do tempo de resposta e do score de eficiência invertida mostraram uma prevalência geral de um processamento coarse-to-fine, independente do campo visual de apresentação. Ainda, os dados da taxa de erro ressaltam o processamento coarse-to-fine realizado pelo hemisfério direito. No geral, esta tese fornece insights sobre assimetria cerebral funcional, integração de alto nível e curso temporal do processamento de FEs, principalmente para aqueles interessados na percepção de faces. Também foi mostrado que operações lateralizadas, tarefa-dependente e coarse-to-fine podem coexistir e interagir no cérebro para processar informação de FE. / Retinal input is decomposed in terms of spatial frequency (SF), i.e., periodic variations of luminance through space. There is extensive literature on the processing of SF in the primary visual cortex. However, it is still unclear how SF information is processed and integrated in high-level vision. This thesis addressed this issue in terms of laterality effects, processing time-course, and the cognitive context in three different sections with specific purposes. These sections behaviorally tackle high-level vision using human faces as stimuli due to their biological and social relevance. In the first section (Theoretical Review) a literature review presented clinical and neurophysiological studies that show brain areas that are involved in face perception and how the right and left hemispheres perform holistic and analytic processing, depending on SF information. The SF hemispheric specialization in face recognition is then reviewed and discussed. Our conclusion is that functional sensorial asymmetries may be the basis for high-level cognitive asymmetries. In addition, we highlighted the role of the processing time. In the second section (Study 1), we psychophysically investigated laterality of low and high SF in face recognition at different exposure times. The SF filtered faces were presented in a divided visual field at high and low temporal constraint in two tasks: face recognition (Experiment 1) and face gender recognition (Experiment 2). In Experiment 1, low and high SF facial information were more efficiently processed in the right and in the left hemisphere, respectively, with no effect of exposure time. In Experiment 2, results showed a right hemisphere asymmetry for low SF faces at low temporal constraint. We concluded that the processing of low and high SF is lateralized in the brain hemispheres for face recognition. However, low and high SF contribution is dependent on the task and the exposure time. In the third section (Study 2), we aimed to investigate which temporal strategy, i.e., coarse-to-fine (from low to high SF) or fine-to-course, each brain hemisphere performs to integrate SF information of human faces in a male-female categorization task. Coarse-to-fine and fine-to-course brief dynamic sequences of faces were presented in the left, right and central visual field. Results of the correct response time and the inverse efficiency score showed an overall advantage of coarse-to-fine processing, irrespective of the visual field of presentation. Data of the error rate also highlights the role of the right hemisphere in the coarse-to-fine processing. All in all, this thesis provided some insights on functional brain asymmetry, high-level integration, and processing time-course of SF information, mainly for those interested in face perception. It was also shown that lateralized, diagnostic-oriented, and coarse-to-fine operations may coexist and interact in the human brain to process SF information.

This experiment investigated lateralized hemispheric regulation of the autonomic nervous system (ANS) among high anxious and nonanxious university undergraduate men using a novel laboratory paradigm. Specifically, this three phase paradigm entailed the administration of a verbal fluency (left frontal) and nonverbal fluency (right frontal) task with or without the threat of a painful stimulus (cold pressor) to high anxious and nonanxious participants. Thus, the cerebrums are hypothesized to be engaged in a dual-task experience requiring the regulation of the ANS and concurrent performance on the verbal or the nonverbal fluency measure. Given the literature which supports relative right hemisphere activation among anxious individuals, it was hypothesized that high anxious men would (1) demonstrate greater physiological arousal to the cold pressor, (2) perform relatively worse on nonverbal fluency measures and demonstrate greater difficulty regulating cardiovascular functioning, and (3) demonstrate relatively lower nonverbal fluency scores and increased physiological arousal when presented with the nonverbal fluency task and cold pressor stimulus simultaneously. The results are evaluated using three perspectives: Heller's (1993) hypothesis, Kinsbourne's Functional Cerebral Distance principle, and lateralized regulation of the sympathetic and parasympathetic nervous system. The results only partially supported the right hemisphere activation hypothesis for anxious individuals, as many of the significant results were counter to hypotheses. Specifically, high anxious men demonstrated lower verbal fluency scores and greater heart rate during the combined stimulus of the cold pressor and verbal fluency task. The data are supportive of relative anterior deactivation among high anxious men. The discussion extends the findings to present questions regarding cerebral regulation of the ANS. Future experiments which may add to the current understanding of lateralized regulation of the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) are suggested. / Ph. D.

No description available.

This study investigated the functional significance of cerebral asymmetries. Width measurements of the human brain were derived from computerized tomographic (CT) films and related to intellectual variables as determined by the Wechsler Adult Intelligence Scale Revised (WAIS-R). Subjects were adults of both sexes who had been referred for neurologic examination and were diagnosed as having no abnormalities (N=28). Reasons for referral included headache, dizziness, or to rule out central nervous system damage following various types of trauma. The asymmetry of hemispheric widths (left minus right) in the frontal, temporoparietal, and occipital areas was correlated with Verbal IQ minus Performance IQ scores within subjects. The difference between verbal and performance IQ scores was used because it reflected an IQ imbalance (IQ-I). Correlations obtained were -.30, -.26, and .06 (respectively). None of these correlations were significant by means of a two-tailed test. There were relationships between particular width asymmetries and individual subtest scores (p≤.05). The Verbal 1 (V1) subtest (Information) was correlated -.50, -.39 and -.47 with brain width asymmetries at 25%, 33% and 50% of the AP distance respectively. V1 correlated .39 with width asymmetry at 80%. Verbal 3 (Vocabulary), verbal 4 (Arithmetic) and verbal 5 (Comprehension) correlated .53 .38, and .39 with width asymmetry at 60% of the AP distance. Performance 1 (Picture Completion) correlated .46 with the width asymmetry at 20% of the AP length. In summary, there does appear to be some specific correlation between individual variation in brain asymmetry and cognitive processing. Relative size of the area of the brain that is involved in a key aspect of a particular cognitive processing may be a factor in the effectiveness of that processing. Further research appears warranted to confirm and clarify a possible relation between anatomical asymmetry and patterns of intellectual ability.

No description available.

Handedness is a widely studied behavioral asymmetry that is commonly measured as a preference for using one hand over the other. Right hand preference in humans occurs at a ratio of 9:1, whereas left hand preference in rhesus monkeys has been estimated at 2:1. Despite differences in the direction and degree of hand preference, this dissertation investigated whether primates share common underlying factors for the development of handedness. Previous work in human infants has identified a predictive relationship between rightward supine head orientation and later right hand preference. Experiment 1 examined the relationship between neonatal head orientation and later hand use in rhesus monkey infants (N=16). A leftward supine head orientation bias was found that corresponded to greater left hand activity for hand-to-face movements while supine; however, neonatal head positioning did not predict later hand use preference for reaching or manipulation on a coordinated bimanual task. A supine posture is common for human infants, but not for rhesus monkey infants, indicating that differences in early posture experience may differentially shape the development of hand use preference. Movement quality is an additional factor that may affect how the hands are used in addition to neonatal experience. 2-D and 3-D kinematic analyses were used to examine the quality of reaching movements in rhesus monkey infants (N=16), human infants (N=73) and human adults (N=12). In rhesus monkey infants, left hand reaches were characterized as ballistic as compared to right hand reaches independent of hand use preference (Experiment 2). Left hand ballistic reaching in rhesus monkeys may be a carryover from earlier primates that relied on very fast reaches to capture insect prey. Unlike monkey infants, reach quality was a function of hand preference in human infants (Experiment 3). By contrast, a right hand advantage for reaching was observed in human adults regardless of left or right hand preference (Experiment 4). Differential hand experience due to hand preference in early infancy may in part be responsible for the hand preference effects on movement quality observed in human infants but not monkey infants. Motor control may become increasingly lateralized to the left hemisphere over human development leading to the right hand advantage for reaching observed in human adults, as well as over primate evolution leading to right hand use preferences in higher primates like chimpanzees. An underlying mechanism such as a right shift factor in humans and a left shift factor in rhesus monkeys may be a common basis for primate handedness. Environmental and experiential factors then differentially shape this mechanism, including species-typical development. Further work examining the ontogeny of hand preference and hemispheric specialization in various primate infants will lead to a greater understanding of how different factors interact in the development of hand use across primate species.

The current research project consists of three experiments on motor asymmetry tasks. Electroencephalogram (EEG) was applied to examine neural activation patterns in coincidence with motor performance across ages. A total of 48 right-handed participants were recruited and conducted the Purdue Pegboard test, graphic test, and aiming test. The three motor tasks were designed to assess functional asymmetry at behavioral level. Brain activities were acquired through EEG while performing the tasks. Measures of EEG signals were mean relative power of 12 electrodes. To examine movement-related brain activity, Mu rhythm within a frequency band of 8 Hz to 12 Hz was filtered with a high-pass of 1 Hz and a low-pass of 50 Hz. Statistical analyses aimed to examine effects of aging on motor asymmetry and hemispheric asymmetry. One-way repeated ANOVA was first conducted on each age group separately to identify motor asymmetry characterized by a significant difference between left hand and right hand. In addition, two-way (Age × Hand) mixed design ANOVA was implemented to examine whether age-related changes in motor asymmetry were significant. The three motor tasks indicated significant motor asymmetry in young adults, with the dominant (right) hand having an advantage over the nondominant (left) hand. However, no significant results were identified in the manual performance of older adults, suggesting reduction of motor asymmetry in aging population. In addition, the two-way ANOVA identified a significant interaction effect between age and hand, which further confirmed the significant changes in motor asymmetry over the life span. Hemispheric activation indicated consistent pattern of changes with motor performance. Hemispheric activation of young adults was strongly lateralized during motor performance, with the frontal regions in the contralateral hemisphere being more activated than the corresponding regions in the ipsilateral hemisphere. On the other hand, hemispheric activation of older adults indicated increased ipsilateral activation which resulted in bilateral and symmetric patterns. The current research substantiated hypothesis proposed in previous motor behavior research that reduced motor asymmetry linked with less hemispheric lateralization in older adults. Based on evidence from motor behavior and neural connectivity, we concluded that aging reduces asymmetries at both behavioral and neural levels.

No description available.

Sixty right-handed men, half classified as anxious without depressive symptoms, the other half as nonanxious, participated in a tachistoscopic study of the influence of anxiety without depression on hemispheric processing of Ekman and Friesen's (1976) happy, angry, and neutral emotional faces. Results were counter to hypotheses, where anxious subjects' reaction times to affective valences were slower than nonanxious subjects. Additionally, anxious subjects failed to demonstrate a negative affective bias for neutral stimuli. Results are discussed in terms of arousal theory, where anxious subjects may be considered overaroused for the tachistoscopic task, thereby exhibiting slower reaction times to affective stimuli. More specific neuropsychological hypotheses for anxious individuals without depression versus nonanxious individuals in terms of concurrent anterior dysfunction and posterior hyperarousal are discussed. / Master of Science

The performance of most tasks requires some interaction between the cerebral hemispheres. Despite this fact, research has focused on demonstrating that each hemisphere is specialised for certain processes and has largely neglected this interaction. ¶ Recent research has recognised the need for a better understanding of how resources are shared between the cerebral hemispheres. While these studies have shed light on factors external to the participants being tested, such as the type of task and stimuli used, presentation times, and different measurement methods, they have neglected variables that differ between individuals. The studies reported here focused on factors internal to the participants. They include sex, age, handedness, functional lateralisation, practice, attention, and hemispheric activation, which vary between individuals or within individuals across time, and have been shown to influence the structure and morphology of the corpus callosum which is the main pathway for hemispheric interactions. ¶ This thesis examines the relationship of these variables to the efficiency of hemispheric interactions. ¶ A literature review of the factors affecting hemispheric interactions and interhemispheric transfer is presented in Chapter 1, and methodological issues relating to the measurement of these variables in Chapter 2. Based upon this research, two tasks, the Poffenberger paradigm and a letter-matching task, were selected to assess interhemispheric transfer time and hemispheric interactions, respectively, and to investigate the relationship between these two variables. ¶ Chapters 3 and 4 present the findings of the principal study, using a large sample of participants and regression analysis, which demonstrate that both faster interhemispheric transfer and more extreme left-handedness are associated with greater efficiency of hemispheric interaction. Surprisingly, other factors which were expected to influence hemispheric interactions (age, sex, functional lateralisation, and attention) did not have a significant effect on this variable. ¶ A strong practice effect found in the task used in Chapters 3 and 4 is analysed in Chapter 5. Contrary to previous findings, this practice effect seems not to be due to a shift from sequential, rule-based processing to memory-retrieval, but rather, is a more general practice effect consistent with progressively more efficient use of neural resources. ¶ Chapter 6 shows that individuals with dyslexia not only demonstrate an abnormally fast interhemispheric transfer, but also attentional deficits, due probably to decreased efficiency in hemispheric interactions. Because some clinical populations, such as individuals with dyslexia, have been shown to have hemispheric interaction deficits, the study of such clinical samples can provide valuable information about the relationship between hemispheric interactions and other individual variables. ¶ In Chapter 7 it is demonstrated that both latent and induced patterns of lateralised hemispheric activation affect hemispheric interactions. This suggests that assessment of hemispheric activation is important not only in this field, but probably also more generally in neuropsychological research. These findings highlight the need for a simple, inexpensive measure of hemispheric activation that can be applied routinely in cognitive experiments. ¶ Chapter 8 presents a new technique to measure lateralised brain activation in typical psychological experiments using functional tympanic membrane thermometry (fTMT). This measure relies on the measurement of ear membrane temperature as an index of hemispheric activation. The technique is simple and inexpensive, and is shown to be suitable for the assessment of hemispheric activation patterns during typical experiments. ¶ In conclusion, individual characteristics such as the efficiency of interhemispheric transfer, handedness, functional lateralisation, attention, and hemispheric activation are important factors to consider when researching hemispheric interactions in both normal and clinical populations. Furthermore, future research will benefit from this newly developed measure, fTMT, by allowing the systematic study of the effects of hemispheric activation in brain processes.