Psychophysical Studies Of Motion Perception In Autism Spectrum Disorders

Introduction Studies have shown considerable evidence of visual dysfunction in Autism Spectrum Disorders (ASD). Motion perception research in ASD reports a superior performance in processing motion information of fine details and neglects global information. However, there are many variabilities in these experimental results, particularly in adults with autism. Several theories have been put forward as the underlying cause(s) of motion deficits in autism. These include: enhanced local domain information processing at early visual area V1; abnormal processing at the higher visual cortical area MST including V5/MT; and/or abnormal functional and structural connectivity between and within cortical networks that are recruited during different motion processing tasks. In this study, we used multiple motion perception tasks in order to activate different visual neural networks that may contribute to perception of specific motion domains in order to understand visual perception abnormalities in autism. The specific aims of each experiment included in this thesis are as follow: • Chapter 3: To investigate the theory of enhanced local details and neglected global picture, using- for the first time- local/global motion coherence stimuli in autism. • Chapter 4: To investigate the neural response biased found in autism in response to radial optic flow. We used optic flow stimuli in self-heading direction discrimination tasks. • Chapter 5: To investigate whether speed parameter is normal in autism-based on the previous outcome- using drifting grating stimuli in a speed discrimination task. Participants and Methods This study recruited two groups of subjects –one with ASD (n = 14), and another with Typical Development (TD) (n= 14), age range (16- 40 years). • Chapter 3 : We used Random Dot Kinatogram (RDK) as global coherence stimuli and employed it in two tasks : (1) Coherent Motion (CM) task, where coherence levels were varied and the subjects had to detect the global direction of the coherent dots, (2) CM with Form From Motion (FfM) stimulus where the FfM consisted of one of four different shapes embedded in the global RDK task. • Chapter 4: We used RDK with optic flow stimuli, which investigated self-direction discrimination in two tasks: angle of eccentricity, and contrast sensitivity. In both tasks we randomized the dot density (15, 80 dots) and speed (4, 10 deg/sec) of the moving stimulus dots. • Chapter 5: We used a pair of drifting gratings with a spatial frequency 2 cycle/ degree, oriented vertically and drifting perpendicular to the direction of orientation, and varied the speed (2, 6 deg/ sec) and the stimuli presentation (250 – 500ms) Results • Chapter 3: Although adults with autism showed comparable performance in reporting global direction similar to the control group, their ability to process global properties, when FfM shape was embedded, declined ( Mean threshold ASD: MC= 13.58, CM-FfM= 30.65) In addition, ASD required more time to respond to global coherence even when their performance was comparable to that of the control group. • Chapter 4: No significant group differences were found for low dot density (15 dots), while high dot (80 dots) density showed low sensitivity to OF motion in the ASD group compared to the TD. Contrast sensitivity task, however, showed lower sensitivity in the ASD group for detecting OF motion when dot density was low (15 dots) and no differences at higher dot density (80 dots) was found. Both tasks showed no group differences in the dot speed changing and no significant differences in response time were observed. • Chapter 5: No group differences (p = 0.226) in sensitivity to speed-discrimination task were found between the ASD and control group in all parameters used in this experiment. The response times were also comparable between both groups (p = 0.855). Conclusions • Chapter 3: Motion perception in ASD found enhanced to local details particularly when motion stimuli involve both local/global information segregation at the same time. We suggest increased internal neural noise and worse external noise filtering as cause of poor global performance in this type of task. • Chapter 4: There were selective impairments in OF processing that may related to altered neural connectivity between the activated visual areas in ASD. Another suggestion might be related to long neural trajectory within higher visual areas, ex. MST. • Chapter 5: Normal motion processing may be found in ASD, however, it this might triggered by task complexity and the visual neural areas that are involved in processing motion information. The overall results suggest selective impairments in visual motion perception in ASD. These impairments would depend upon the task requirements and therefore on the activated visual networks that contribute to different aspects of motion information processing. The present studies provide novel findings in defining deficits in motion perception in autism, which thereby may contribute in understanding disturbed visual function in ASD

Numerical evaluation of the soil behavior during impact driving of pipe-piles

During the impact driving of pipe-piles, the soil is influenced in different ways including the void ratio, stress distribution, and plugging formation. Such effects may play an important role in structural design criteria such as the pile’s lateral support provided by the soil. Hence, this work is focused on investigating the change in the mechanical characteristics of the soil during impact driving using an advanced numerical analysis tool which is validated against an experiment. The investigation includes the pile penetration behavior, plugging formulation inside the pile, and the change of the lateral stress in the soil during the pile installation. The proposed numerical model is shown to provide similar results compared to experimental measurements. The void ratio of the soil is influenced due to pile driving up to a lateral and vertical distance of 2D and 1D, respectively, where D is the pile diameter. Compared to the initial void ratio, the soil inside the pile experienced loosening about 20% while the soil outside is densified about 30% during driving. Moreover, the induced lateral stress inside is more than the one outside the pile, indicating the formation of plugging. Compared to the initial lateral stress state, the pile installation increased the lateral stress up to four times inside and two times outside the pile. Based on the findings of this work, the effects of driving on soil mechanical properties are not minimal and may affect the pile performance including the lateral resistance of the pile. By using the numerical approaches such as one in this study, the evaluation of the various effects on the soil due to pile driving and gaining a better understanding of the such complex problems are possible

Numerical evaluation of the pipe-pile buckling during vibratory driving in sand

The buckling of steel pipe piles during vibratory driving is numerically studied using the Multi-Material Arbitrary Lagrangian-Eulerian (MMALE) method. This method handles the large soil deformations that occur during pile driving and other geotechnical installation processes. The Mohr-Coulomb and an elastic-perfectly plastic material model are used to model the soil and the pile mechanical behavior, respectively. The result of a small-scale pile driving experiment is used to validate the numerical model. The penetration trend agrees well with the experimental measurements. Thereafter, four case scenarios and their possible effects on pile buckling, namely the presence of heterogeneity in the soil (a rigid boulder inside the soil) and the existence of geometrical imperfection modes in the pile (ovality, out-of-straightness, flatness) are investigated. This study shows that a combination of local and global buckling initiates at the pile tip and the pile shaft, respectively. During the initiation of buckling, a decrease in the penetration rate of the pile is observed compared to the case where no or minimal buckling occurs. It is shown that a less portion of the driving energy is spent on the pile penetration and the rest is spent on other phenomena such as buckling, resulting in less pile penetration. The cross section of the pile tip after buckling takes a form of a “peanut”, yet with a different geometry for each case. In cases where the model was initially symmetric, an asymmetric shape in cross section of the pile tip was obtained at the final stage which can be attributed to complex soil-structure interaction. The results of the numerical approach provide promising results to be used as an evaluation tool to reach reliable predictions in pile installation practice

Investigation of Mesh Improvement in Multimaterial ALE Formulations Using Geotechnical Benchmark Problems

This material may be downloaded for personal use only. Any other use requires prior permission of the American Society of Civil Engineers. This material may be found at https://doi.org/10.1061/(ASCE)GM.1943-5622.0001723.Two of the mesh-based numerical approaches suitable for geotechnical large deformation problems, the multimaterial arbitrary Lagrangian–Eulerian (MMALE) and the coupled Eulerian–Lagrangian (CEL) methods are investigated. The remeshing step in MMALE was claimed to hold advantages over CEL, but its effects on application problems are not studied in detail. Hence, the possible capabilities and improvements of this step are studied in three large deformation geotechnical problems with soil–structure interaction. The problems are validated and verified using experimental and analytical solutions, respectively. By using the remeshing step in MMALE, a smoother material interface, lower remap related errors, and better computation costs are achieved

Numerical evaluation of the soil behavior during pipe-pile installation using impact and vibratory driving in sand

Pipe-piles are installed using impact or vibratory driving which influences the soil in different ways including the void ratio and stress distribution. Such complex problems are hard to investigate on the field as well as using numerical methods. Here, a sophisticated numerical approach is employed to evaluate the soil behavior during pile installation. Also, a sensitivity analysis on the frequency and the impact duration is done for vibratory and impact driving, respectively. The investigation includes the required force of the pile installation, pile penetration behavior, plugging formation inside the pile, and the change of the soil state including the change in the horizontal stress and density around the pile during the installation. Results of the numerical model show several advantages of vibratory driving over impact driving in the dense sand including, reaching the designated depth using less momentum and work as well as more soil compaction

Numerical evaluation of buckling in steel pipe piles during vibratory installation

The buckling of steel pipe piles during installation is numerically studied. Generally, numerical simulation of installation processes is challenging due to large soil deformations. However, by using advanced numerical approaches like Multi-Material Arbitrary Lagrangian-Eulerian (MMALE), such difficulties are mitigated. The Mohr-Coulomb and an elastic-perfectly plastic material model is used for the soil and pile respectively. The pile buckling behavior is verified using analytical solutions. Furthermore, the model is validated by an experiment where a pipe pile is driven into sand using vibratory loading. Several case scenarios, including the effects of heterogeneity in the soil and three imperfection modes (ovality, out-of-straightness, flatness) on the pile buckling are investigated. The numerical model agrees well with the experimental measurements. As a conclusion, when buckling starts, the penetration rate of the pile decreases compared to the non-buckled pile since less energy is dedicated to pile penetration given that it is spent mainly on buckling

Einsatz der Multi-Material-ALE-Methode unter Verwendung eines nichtlinearen Stoffgesetzes zur Simulation der großen Verformungen in geotechnischen Installationsproblemen

Numerical simulation of geotechnical installation problems, specifically offshore pile installation problems pose several challenges including the treatment of large deformation using the conventional finite element method (FEM), capturing the non-linear behavior of the soil, and the presence of pore water in the porous medium. In this work, a clear and straightforward approach for modeling large deformation problems is developed which addresses the three aforementioned considerations. During the last decades, efforts have been made to tackle the problems associated with large deformation during the simulation of pile installation. In this thesis, the Multi-Material Arbitrary Lagrangian-Eulerian (MMALE) is employed to address the large deformation problem. Briefly, the method consists of three sub-steps, a Lagrangian step, a remeshing step, and a remapping step, which are performed sequentially owing to the operator-split scheme. The advantage of the MMALE with a special focus on the remeshing step is discussed thoroughly using various benchmarks. Beside a robust element formulation, a sophistical constitutive equation is required to capture the soil realistic behavior in large strains due to penetration. The mechanical behavior of granular materials like sand is highly nonlinear due to the presence of an evolving internal structure formed by the grains. The strength and stiffness are generally a function of the stress and density state and the loading history. A constitutive equation based on hypoplastic framework is chosen and defines evolution equations for the effective stress, void ratio, and the so-called intergranular strain tensor suitable for simulating cyclic loading effects. Interfaces are implemented in two hydrocodes to employ hypoplastic constitutive equation. Additionally, the presence of water is inevitable in offshore projects and needs to be considered in the numerical evaluation. Hence, a simplified coupled formulation is introduced to the developed code to consider the presence and effects of pore water in the soil behavior. Finally, the approach is verified and validated by various analytical and experimental geotechnical benchmarks, respectively. Also, the method is used to study the pile buckling during pile installation under different boundary conditions.Die numerische Simulation von geotechnischen Installationsproblemen, beispielsweise von Offshore-Pfählen, ist mit mehreren Herausforderungen verbunden, darunter die Behandlung großer Verformungen mit der Finite-Elemente-Methode (FEM), die Erfassung des nichtlinearen Verhaltens des Bodens und die Berücksichtigung des Vorhandenseins von Porenwasser im Boden. In den letzten Jahren wurden einige Anstrengungen unternommen, um diese Fragestellungen bei der Simulation von Pfahlinstallationsproblemen in geeigneter Weise zu behandeln. In der vorliegenden Arbeit wird ein Ansatz zur Modellierung großer Verformungsprobleme entwickelt, der die zuvor genannten Punkte berücksichtigt. Als Grundlage wird eine Multi-Material Arbitrary Lagrangian-Eulerian (MMALE) Methode verwendet, um die großen Verformungen bei der Pfahlinstallation numerisch zu simulieren. Das Verfahren besteht aus drei Teilschritten - einem Lagrange-Schritt, einem Remeshing-Schritt und einem Remapping-Schritt, die aufgrund des Operator-Split-Schemas nacheinander durchgeführt werden. Der Vorteil der MMALE Methode mit besonderem Fokus auf den Remeshing-Schritt wird anhand verschiedener Benchmarks diskutiert. Neben einer robusten Elementformulierung ist eine nichtlineare Stoffgesetzgleichung erforderlich, um das Bodenverhalten bei großen Verformungen realitätsnah zu erfassen. Das mechanische Verhalten von körnigen Materialien wie Sand ist vor allem aufgrund des Vorhandenseins seiner inharenten von den Körnern gebildeten Struktur stark nichtlinear. Die Festigkeit und die Steifigkeit eines Sandbodens sind im Allgemeinen eine Funktion des Spannungs und Dichtezustands und der Belastungsgeschichte. Es wird eine auf der Hypoplastizität basierende Konstitutivgleichung gewählt, die Evolutionsgleichungen fur die effektive Spannung, die Porenzahl und den sogenannten intergranularen Dehnungstensor, der zur Simulation von zyklischen Belastungen geeignet ist, enthält. Über Schnittstellen wird dieses Stoffgesetz in zwei FE-Programme implementiert. Darüber hinaus wird eine vereinfachte gekoppelte Formulierung zur Simulation von Porenwasserdruckentwicklung in den Code implementiert. Die Modellansätze werden durch verschiedene analytische und experimentelle geotechnische Benchmarks verifiziert und validiert. Das entwickelte numerische Modell wird schließlich verwendet, um das Verhalten eines offenen Stahlrohrpfahls während der Einbringung unter verschiedenen Randbedingungen zu untersuchen

Do different experimental tasks affect psychophysical measurements of motion perception in autism-spectrum disorder? An analysis

Asmaa Bakroon,1 Vasudevan Lakshminarayanan1–3 1Theoretical and Experimental Epistemology Laboratory, School of Optometry and Vision Science, University of Waterloo, Waterloo, ON, Canada; 2Departments of Physics and Systems Design Engineering, University of Waterloo, Waterloo, ON, Canada; 3Department of Computer Engineering, University of Waterloo, Waterloo, ON, Canada Abstract: There is a rapid increase in the number of individuals with high-functioning autism (HFA). Research on motion perception in HFA has shown deficits in processing motion information at the higher visual cortical areas (V5/middle temporal). Several hypotheses have been put forth to explain these deficits as being due to enhanced processing of small details at the expense of the global picture or as a global integration abnormality. However, there is a lot of variability in the results obtained from experiments designed to study motion in adults with autism. These could be due to the inherent diagnostic differences within even the same range of the autism spectrum and/or due to comparison of different experimental paradigms whose processing by the same visual neural areas could be different. In this review, we discuss the various results on motion processing in HFA, as well as the theories of motion perception in autism. Keywords: autism-spectrum disorder, high-functioning autism, motion perception, biological motion, form perception, random-dot kinematogram, local motion, global motion&nbsp

Dataset of CM and CM-FfM tasks

Our Hypothesis was to study whether global motion perception in autism decline if Form-from motion (FfM) details embedded in the global picture. We conducted data from 14 adults with autism IQ> 75 and 14 adults with same age, gender, and academic level from a control group. We used the RDK stimulus to generate different levels of coherent motion, and we measured the threshold ( minimum number of dots that run in one direction are required to define the direction of the coherent dots), in on task of coherent motion (CM) and compared with the threshold with the same task but with embedding a Form-from motion shape that moved in the center of the stimulus and in 45 degree from the direction of the coherent dots. We collected the following data: the threshold of CM and CM-FfM tasks, the average response time for both tasks, and the percentage of correct responses to the shape at each coherent levels. Results showed that in CM task, both groups showed similar performance, however, when the FfM shape was embedded, the autism group performance declined dramatically. In our publication of " Is Global Motion Perception Affected in Adults with Autism When Form-from Motion Stimulus is Embedded ?" we explained more about what could be behind this global/local biased of motion perception in autism

Threshold and mean response time taken from psychophysical optic flow motion experiments to determine eccentricity discrimination and contrast sensitivity in adults with autism compared to control group.

In Eccentricity task: threshold, is the minimum eccentricity angle measured by degrees from the central heading line. It indicates that participant was able to identify accurately the direction of heading of optic flow motion. A higher threshold means low sensitivity. This threshold was measured as a dependent value for each participant at each parametric value using adaptive staircase method. In Contrast task: threshold presents the minimum dots luminance that participant was able to identify accurately the direction of optic flow motion. Different contrast levels were achieved by changing the luminance of dots with respect to the uniform gray background using an adaptive staircase method. Higher threshold also indicate low sensitivity. Response time, is the time taken for the participants to response to the direction of optic flow motion at each parameter level and in both tasks. Time was taken from the stimulus end until the participant press the keypad to response. Time input is in millisecond