This paper presents a decision theory model of the perceptual processes by which an observer compares two visual stimuli presented at different points in time and at different locations in the visual field. The model specifies how information about the first stimulus is lost during the interstimulus delay and over the spatial translation required for the comparison. Emphasis is placed on the manner in which the effect of temporal separation combines with the effect of spatial separation in determining the observer's sensitivity. Two experiments are reported. The observer was required to discriminate a difference in vertical position between two laterally separated points of light presented successively in the dark. The progressive loss in sensitivity with increasing temporal and spatial separations is consistent with the predictions of the model. / Thesis / Doctor of Philosophy (PhD)

The human brain is considered to be the most complex and powerful information-processing device in the known universe. The fundamental concepts behind the physics of complex systems motivate scientists to investigate the human brain as a collective property emerging from the interaction of thousand agents. In this dissertation, I investigate the emergence of cooperation-induced properties in a system of interacting units. I demonstrate that the neural network of my research generates a series of properties such as avalanche distribution in size and duration coinciding with the experimental results on neural networks both in vivo and in vitro. Focusing attention on temporal complexity and fractal index of the system, I discuss how to define an order parameter and phase transition. Criticality is assumed to correspond to the emergence of temporal complexity, interpreted as a manifestation of non-Poisson renewal dynamics. In addition, I study the transmission of information between two networks to confirm the criticality and discuss how the network topology changes over time in the light of Hebbian learning.

Temporal representation in the brain has been recently acknowledged as a fundamental mechanism underlying short-term memory (STM). Nonetheless, the existing body of research presents conflicting results on the extent of this relationship. Some studies propose that rhythmic disruption adversely affects perception and comprehension, and regular rhythm has been associated with the facilitative impact on STM tasks, while others suggest that its influence on STM tasks might not be as substantial. This thesis delves into rhythmic irregularity's impact on STM, particularly when an internally established rhythm is disrupted. Through two verbal STM tasks – the jabberwocky memory task and the Urdu memory task – conducted with thirty participants (31 females), involving the repetition of sentences in native English or foreign Urdu, this experiment investigates whether manipulating the speed of target sentences in relation to prime phrases affects the accuracy of sentence repetition in the assigned tasks. Our hypothesis posited that STM for sentences presented at altered speeds, either slower or faster, would be compromised compared to sentences at a normal pace. However, the outcomes of our study did not reveal any significant differences in repetition accuracy across the three speed conditions within the two STM tasks. Interestingly, our investigation uncovers two noteworthy findings. Firstly, variations in repetition accuracy among the three speed conditions appear to be influenced by participants' bilingual or multilingual backgrounds. Bilingual and multilingual individuals exhibited better performance under slow speed conditions at the syllable level, while monolingual participants displayed enhanced recall accuracy for whole words in the normal speed condition. Secondly, a discrepancy emerges between participants' self-perceived performance across the three speech conditions and their actual performance. These findings emphasize the potential roles of linguistic background and metacognition in shaping both temporal representation and STM performance, thereby prompting further exploration of these intricate interactions. / Thesis / Master of Science (MSc) / Our ability to remember spoken language, or phonological content, is closely tied to how we perceive its rhythm and timing. When we hear speech, our brain processes not just the words but also the temporal structure of the context. This temporal organization helps to retain spoken information, and our ability to remember speech in turn predicts how well we can learn new words in a foreign language. This suggests that the rhythmic patterns of words and their sentence contexts might play a crucial role in how we organize and remember linguistic content. The brain’s rhythms naturally synchronize with the rhythms of speech, influencing comprehension. However, when this synchronization is disrupted – for instance, when a speaker changes their pace suddenly – comprehension may be impeded. On the other hand, while studies have shown that memory for digits is not affected by their presentations at different rhythmic regularities, the way the brain processes disruption of internally driven rhythms might differ from how it processes externally driven rhythms. This thesis explores these rhythmic influences on memory by conducting tasks involving repeating sentences in native English and the foreign Urdu language to see how sudden changes in rhythm impact memory. This sheds light on the mechanisms by which the brain handles different time-related aspects of language and how this affects the memory retention, which ultimately shapes language skills and learning abilities.

This thesis investigated developmental changes in temporal perception of hearing and touch (audiotactile). Three empirical chapters provide converging evidence on the unique characteristics of this modality pairing. In Chapter 2, a simultaneity judgment task assessed temporal perception. Three groups of children (aged 7-, 9-, and 11-years-old) were compared to a group of adults, examining measures such as the temporal simultaneity window and the point of subjective simultaneity. By age 11, mature temporal perception between hearing and touch was observed. Chapter 3 investigated developmental changes in temporal-based integration using the fission and fusion illusions. The study involved comparing three groups of children to adults (aged 9-, 11-, and 13-years-old). The measure of illusion strength combined with a signal detection analysis demonstrated that children did not exhibit adult-like integration until around age 13. Chapter 4 explored the potential impact of short-term congenital visual deprivation on hearing and touch temporal perception. An audiotactile simultaneity task was used to test a group of adults who received treatment for congenital bilateral cataracts. The results of this final experiment are considered preliminary because of limitations imposed by the COVID-19 pandemic; instead of the planned age- and gender-matched control participants, we utilized the adult data from Chapter 2 for comparison. The General Discussion provides a comprehensive account of how these findings relate to one another and how they situate in the broader literature. Additionally, a novel hypothetical theory is presented, incorporating the established causal inference framework, to offer insights into observed changes in multisensory perception across development. / Thesis / Doctor of Philosophy (PhD) / Perception relies on combining information from our senses. Multiple cues determine whether we integrate or segregate sensory information. Timing provides one crucial cue. Children's timing perception requires development to reach the same precision as adults. Most studies on the development of time perception between the senses have included vision. However, this thesis investigated the development of time perception between hearing and touch. The first two empirical chapters explored typical development using complementary tasks, while the third empirical chapter investigated the impact of congenital cataracts on timing perception. By studying children with cataracts who underwent early cataract removal, we can observe the effects of visual deprivation on these senses. These chapters shed light on the development of audiotactile temporal perception and propose that different combinations of senses may develop independently.

Exercise is emerging as a promising low-cost intervention to mitigate age-related memory decline and promote successful aging. Aerobic exercise training enhances cardiorespiratory fitness (CRF) and improves integrity of the medial temporal lobe (MTL) memory system. The hippocampus, a brain region located within the MTL, is critically involved in episodic and spatial memory formation, including spatial navigation, and demonstrates subfield-specific plasticity in response to aerobic exercise among both animals and young adult humans. Yet it remains unclear whether hippocampal subfield-specific exercise training and CRF effects also extend to older adults. Another modulator of structural and functional integrity of the MTL is chronic stress. Importantly, chronic stress was shown to predominantly impact brain regions such as the hippocampus and associated cognitive functions, including episodic memory, that are highly vulnerable to the effects of chronic stress and decline with age. Allostatic load (AL), or the integrative biological dysregulation of multiple biological systems resulting from chronic stress, is associated with poorer cognition, and reduced structural brain integrity. Black Americans were shown to have high burden of AL compared to non-Hispanic White Americans, and this was associated with reports of greater perceived discrimination, a salient psychosocial stressor, among the former group. Although race is a sociocultural construct, Black-White disparities exist in cognitive task performance, and risk of Alzheimer’s disease (AD) and dementia, with Black Americans displaying significantly worse cognitive task performance scores, and a greater likelihood to be diagnosed with AD and dementia compared to non-Hispanic White Americans. Thus, greater AL and discriminatory experiences in Black compared to non-Hispanic White older adults may underlie the racial disparity in neurocognitive aging. The goal of this dissertation was to examine the opposing impact of chronic stress and exercise on neurocognitive aging. This was accomplished by 1) investigating aerobic exercise intervention effects on hippocampal subfield volume and fMRI activity during spatial navigation, a complex cognitive function that declines with age and that is, in part, supported by the MTL (Project 1), 2) examining the effect of AL as a cumulative, physiological stress measure on neurocognitive aging (Project 2), and 3) examining the effect of chronic psychosocial stress through the lens of social discrimination on the functional connectivity of the MTL subsystem of the default mode network, a resting state network that has been linked to episodic memory (Project 3). The secondary aim of this dissertation was to look at the effect of AL (Project 2) and social discrimination (Project 3) on racial neurocognitive disparities in cognitively intact older Black and non-Hispanic White adults. In the first project, data from two randomized controlled clinical trials of aerobic exercise intervention targeting healthy, initially sedentary adults aged 55-85 years were used to examine the effect of exercise training and exercise-related CRF on the hippocampal integrity on the subfield level. Both randomized controlled trials randomly assigned participants to either: aerobic exercise group or active control group and underwent baseline and end-of-study fitness testing, cognitive testing, and high resolution structural and functional MRI. The first objective of this project aimed to test whether aerobic exercise training increases CRF level, which, in turn, increases anterior hippocampal subfield volume and/or attenuates volumetric decline among older adults undergoing aerobic exercise training compared to those in the active control group. Partially supporting our prediction, results displayed that following the period of the 12-week exercise intervention, the active control group but not the aerobic exercise group showed a right dentate gyrus (DG) head volumetric decline that was trending toward statistical significance. Additionally, a positive significant association between changes in CRF and left subiculum (SUB) head volume following the exercise intervention among women was found. The second objective sought to examine whether aerobic exercise intervention modulates the activation in the hippocampus in a subfield-specific manner during virtual reality navigation task performance, particularly modulating activation in the SUB subfield. Consistent with our structural results an increase in CRF was associated with a decrease fMRI activity in the left SUB. Whole-brain analysis during virtual reality navigation task performance showed that an increase in CRF was associated with a decrease in fMRI activity in the cuneus and right middle frontal gyrus, both brain regions that repeatedly display activation during virtual navigation. In the second project, existing data from the Framingham Heart Study (FHS) was used. Cognitively intact men and women, who identified as either Black or African American from the first multiracial Omni group 1 cohort (OMNI1), or White non-Hispanic from the second-generation cohort (Gen2), and were native English speakers, were included in the study. AL was calculated using the values for 10 biomarkers available in the FHS database for the two cohorts studied that are biomarkers for immune, metabolic, and cardiovascular system function. The objective of this project sought to test the prediction that AL correlates with cognitive function and brain structures, particularly hippocampal volume. We additionally sought to examine the secondary prediction that AL mediates the relationship between race and cognitive task performance and structural brain integrity, in age- sex- and education matched racial groups of cognitively intact older adults after controlling for quality of education, cardiovascular-related comorbidities and depression in the FHS cohorts. Results demonstrated that there was no significant correlation between AL and cognitive and brain volumetric measures, however there were significant Black-White disparities in cognitive task performance in verbal and visual learning and memory, abstract reasoning and attention span. These Black-White cognitive task performance disparities existed even after controlling for quality of education, and cardiovascular-related comorbidities. Although there was no significant racial disparity in the mean score of AL index, our physiological stress measure, AL partially explained the observed Black-White disparity in cognitive task performance in verbal learning and memory. Importantly the observed AL effect was not driven by the cardio-metabolic component biomarkers that are part of the AL index, known to overlap with cardiovascular risk factors, but rather, the AL index drove this effect as a whole. There were no racial disparities in brain volumetric measures after controlling for cardiovascular-related comorbidities. Furthermore, there were no sex differences in the effect of AL in any of our neurocognitive outcome measures. In the third project, cognitively intact older Black and White adults (aged 55-80 years) were recruited from the greater Boston area. To measure perceived social discrimination, participants were asked to complete the Experiences of Discrimination questionnaires. Additionally, participants underwent fMRI scanning to examine the functional connectivity of resting-state brain networks. This project sought to test the prediction that greater perceived everyday discrimination would be associated with alteration of resting state functional connectivity, particularly in the MTL subsystem. Results showed that greater perceived everyday discrimination predicted stronger resting-state connectivity between the MTL subsystem, and a cluster located in the right control network, suggesting that perceived discrimination, a psychosocial stressor, may cause functional alteration in brain networks supporting memory and cognitive control in older adults. In conclusion, findings of these studies suggest a neuroprotective effect of exercise, where exercise may attenuate aging-related decline in the structure and function of hippocampal subfields, especially among women, and possibly by targeting the SUB. Furthermore, findings of these studies suggest stress related mechanisms underlying neurocognitive integrity, particularly in the MTL memory system.

Monocular 6DoF pose tracking has many applications in augmented reality, robotics and other areas and because of the rise of deep learning new approaches such as category-level models are successful. The temporal information in sequential data is essential for both online and offline tasks, which can help boost the quality of predictions while encountering some unexpected influences like occlusions and vibration. In 2D object detection and tracking, substantial research has been done in leveraging temporal information to improve the performance of the model. Nevertheless, it is challenging to lift the temporal processing to 3D space because of the ambiguity of the visual data. In this thesis, we propose a method to calculate the temporal difference of points and pixels assuming that the K nearest points share similar features. The extracted features from the difference are learned to weigh the relevant points in the temporal sequence and aggregate them to provide support to the current frame's prediction. We propose a novel difference-based temporal module to incorporate both RGB and 3D points data in a temporal sequence. This module can be easily integrated with any category-level 6DoF pose tracking model which uses RGB and 3D points as input. We evaluate this module on two state-of-the-art category-level 6D pose tracking models and the result shows that it can increase the model's accuracy and robustness in complex scenarios.

Samtidigt som universitetsstudier förutsätts av att förhålla sig till deadlines visar uppskattningar att 80 till 95 procent av universitetsstudenter prokrastinerar, förhalar studierna, vilket kan påverka både studieprestation och välbefinnande negativt. Syftet med denna studie var att undersöka om faktorerna i Temporal Motivational Theory (TMT): förväntan, värde, känslighet för fördröjning och fördröjning kunde predicera prokrastinering hos studenter. Detta utifrån hypotesen om att hög förväntan och högt värde leder till minskad prokrastinering, samtidigt som hög känslighet för fördröjning och hög fördröjning leder till ökad prokrastinering. En enkät genomfördes av 165 studenter vid Linnéuniversitetet. Multipel regressionsanalys användes där faktorerna tillsammans kunde visa 54,9 procent förklarad varians, där känslighet för fördröjning och fördröjning hade störst effekt. Sammantaget hade dels värde betydelse, där sådant som väckte känslor av olust eller obehag förhalades. Känslighet för fördröjning och fördröjning hade också betydelse, där egenskaperna impulsivitet, distraherbarhet och bristande självkontroll ledde till mer förhalning desto längre bort en deadline var i tid. Däremot hade förväntan, en individs tro på den egna förmågan, ingen signifikant effekt på prokrastinering. / University studies implies a need for students to meet deadlines. At the same time, estimates indicate that 80 to 95 percent of university students procrastinate, postpone studies, which can negatively affect both academic performance and well-being. The aim of this study was to investigate whether the factors of Temporal Motivational Theory (TMT): expectancy, value, sensitivity to delay and delay could predict procrastination in students. This is based on the hypothesis that high expectancy and high value results in reduced procrastination, while high sensitivity to delay and high delay lead to increased procrastination. A survey was completed by 165 students at Linnaeus University. Multiple regression analysis was used where the factors together showed 54.9 percent explained variance, where sensitivity to delay and delay had the greatest effect. Overall, value was important, where tasks that aroused feelings of displeasure or discomfort were postponed. Sensitivity to delay and delay also mattered, with the traits of impulsivity, distractibility and lack of self-control leading to more procrastination the further away a deadline was in time. In contrast, expectancy, an individual's belief in one's own ability, had no significant effect on procrastination.

Spatio-temporal satellite image analysis is a technique for monitoring spatial and temporal changes of land cover and oceanic locations on earth. Temporal Map Algebra (TMA) is a novel technique developed by Jeremy Mennis and Roland Viger for analyzing a time series of satellite imagery using simple algebraic operators that treats time series of imagery as a threedimensional data set, where two dimensions encode planimetric position on earth surface and the third dimension encodes time. The high dimensionality of raster data leads to high computational cost, which is why parallel computation is attractive. This thesis describes the design, implementation, andmperformance evaluation of parallel compositing of vegetation indices derived from MODIS datasets using TMA.

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