Contact inhibition of locomotion (CIL), a migratory mechanism, first introduced by Abercrombie and Heaysman in 1953 is now a fundamental driving force in developmental, repair and disease biology. Much of what we know of CIL stems from studies done on 2D substrates which are unable to provide the essential biophysical cue of fibrous extracellular matrix curvature. Here we inquired if the same rules are applicable for cells attached to and migrating persistently on suspended and aligned ECM-mimicking nanofibers. Using two elongated cell shapes (spindle attached to one fiber, and parallel attached to two fibers), we quantitate CIL rules for spindle-spindle, parallel-parallel and spindle-parallel collisions. Two approaching spindles do not repolarize upon contact but rather continue to migrate past one another. Contrastingly, approaching parallel cells establish distinct CIL, with only one cell repolarizing upon contact followed by migration of both cells as a cohesive unit in the repolarization direction. Interestingly, for the case of spindle and parallel cell collision, we find the parallel cell to shift the morphology to that of spindle and continue persistent movement without repolarization. To account for effect of cell speed, we also quantitate CIL collisions between daughter and non-dividing cells. While spindle-spindle collisions result in cells still walking by, for parallel-parallel collisions, we capture rare events of a daughter cell pushing the non-dividing cell. With increasing population numbers, we observe formation of cell streams that collapse into spheroids. Single cells are able to invade along fibers from the spheroids and are then subject to same CIL conditions, thus providing a platform with cyclic CIL. The presented coupling of experimental and analytical framework provides new insights in contextually relevant CIL and predictive capabilities in cell migration decision steps. / Master of Science / Contact inhibition of locomotion (CIL) is a migratory process that can lead to a change in migration direction through protrusion inhibition of single cells. First described in 1953, the traditional model of CIL shows that on a 2D substrate, two migrating cells experience a decrease in protrusive behavior upon contacting each other, followed by repolarization, and migration away from one another. However, a cell's extracellular matrix (ECM) is fibrous in nature, and how cells maintain standard CIL rules in fibrous environments remains unclear. Here, using suspended, aligned nanofibers created using a non-electrospinning Spinneret based Tunable Engineered Parameters (STEP) method, we investigate CIL decision steps of two fibroblast cells approaching each other in two shapes: spindle cells attached to single fibers, and parallel cells attached to two fibers. Most spindle cells approaching each other do not switch direction upon contact, but rather continue to migrate past each other, termed a walk past. Contrastingly, approaching parallel cells display unique CIL whereby only one cell repolarizes and reverses its migration direction. Subsequently, both cells remain in contact while migrating in the repolarization direction. Interestingly, we report that both spindle and parallel CIL are also affected by speed post cell division. Altogether, for the first time, we introduce a platform to understand cell shape driven CIL geometrical rules in ECM mimicking environments.

The Virtual Reality (VR) industry has experienced growth in recent years with companies such as HTC, Meta, and Valve releasing more consumer-grade headsets. While certain companies such as Meta are pushing for more productivity focused applications of VR, VR remains a primary target for games. Locomotion is still a fundamental problem in games and other applications. Over the years, many researchers have examined application-agnostic and domain-specific techniques. However, few studies have been conducted on techniques specific for the environments and challenges found in first-person games. This thesis contributes with the design and evaluation of new locomotion techniques for VR games. We conducted a user study with 27 participants to evaluate one novel techniques (Repeated Short-Ranged Teleports (RSRT)), a node-based technique (Continuous Movement Pads (CMP)), and a grabbing metaphor (World Grab) with popular techniques (Smooth Locomotion, Teleport). Most preferred by participants, we found that CMP could be a suitable alternative for games compared to Smooth Locomotion and Teleport based on performance data such as time, damage taken, overall usability from System Usability Scale Questionnaires, and overall workload measured from the NASA Task-Load Index Questionnaire. We also found that RSRT and World Grab were least preferred overall and performed measurably worse in terms of time, number of falls in a section designed to measure precision and accuracy, usability, and overall workload. / Master of Science / The Virtual Reality (VR) industry has experienced growth in recent years with companies such as HTC, Meta, and Valve releasing more consumer-grade headsets. While certain companies such as Meta are pushing for more productivity focused applications of VR, VR remains a primary target for games. Locomotion or movement within VR is a problem that does not just have one answer. There are many ways to move around in VR, with many researchers having examined the topic. This thesis explores the different methods of VR locomotion and provides information about a user study conducted regarding several novel techniques. We conducted a user study with 27 participants to evaluate one novel techniques (Repeated Short-Ranged Teleports), a node-based technique (Continuous Movement Pads), and a method (World Grab) based on a metaphor for moving in VR with more traditional techniques (Smooth Locomotion, Teleport). Based on the results of the study, we found that Continuous Movement Pads could be a suitable alternative for games compared to Smooth Locomotion and Teleport based on performance data and qualitative analysis of participants' preferences. However, we also found that Repeated Short-Ranged Teleports and World Grab were least preferred overall.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / Cette étude a pour but de mieux comprendre la contribution des faisceaux descendants des quadrants ventraux et ventrolatéraux de la moelle épinière, telles que les voies réticulo- et vestibulospinales, dans le contrôle de la locomotion chez le chat adulte. Des études antérieures (Eidelberg 1981 et Afelt 1974) suggéraient que ces faisceaux étaient "essentiels et nécessaires" à la locomotion. Leur conclusion était cependant basée principalement sur des lésions spinales ne laissant que de petites parties de tissus intacts dans les portions ventrales et ventrolatérales. Ce protocole ne permettait donc pas de déterminer l'habilité et la capacité de marcher en l'absence de ces voies descendantes. La première phase de cette étude a pour but de clarifier l'apport de ces voies descendantes en utilisant une nouvelle approche qui consiste à pratiquer des lésions des quadrants ventraux et ventrolatéraux au niveau thoracique en laissant intactes les voies dorsolatérales, telles que les voies rubrospinales et corticospinales. Ce type de lésion a permis de cerner l'apport des voies ventrales et ventrolatérales dans le contrôle de la locomotion. De plus, il a été possible d'évaluer si les voies descendantes encore présentes dans les quadrants dorsolatéraux étaient suffisantes pour maintenir un rythme locomoteur en l'absence de ces voies ventrales et ventrolatérales si importantes dans le contrôle de la locomotion.

The Multi-Appendage Robotic System (MARS) built for this research is a hexapod robotic platform capable of walking and performing manipulation tasks. Each of the six limbs of MARS incorporates a three-degree of freedom (DOF), kinematically spherical proximal joint, similar to a shoulder or hip joint; and a 1-DOF distal joint, similar to an elbow or knee joint. Designing walking gaits for such multi-limb robots requires a thorough understanding of the kinematics of the limbs, including their workspace. The specic abilities of a walking algorithm dictate the usable workspace for the limbs. Generally speaking, the more general the walking algorithm is, the less constricted the workspace becomes. However, the entire limb workspace cannot be used in a continuous, statically stable, alternating tripedal gait for such a robot; therefore a subset of the limb workspace is dened for walking algorithms. This thesis develops MARS limb workspaces in the knee up conguration, and analyzes its limitations for walking on planar surfaces. The workspaces range from simple 2D geometry to complex 3D volumes. While MARS is a hexapedal robot, the tasks of dening the workspace and walking agorthm for all six limbs can be abstracted to a single limb using the constraint of a tripedal, statically stable gait. Based on understanding the behavior of an individual limb, a walking algorithm was developed to allow MARS to walk on level terrain. The algorithm is adaptive in that it continously updates based on control inputs. Open Tech developed a similar algorithm, based on a 2D workspace. This simpler algorithm developed resulted in smooth gait generation, with near-instantaneous response to control input. This accomplishment demonstrated the feasibility of implementing a more sophisticated algorithm, allowing for inputs of all six DOF: x and y velocity, z velocity or walking height, yaw, pitch and roll. This latter algorithm uses a 3D workspace developed to aord near-maximum step length. The workspace analysis and walking algorithm development in this thesis can be applied to the further advancement of walking gait generation algorithms. / Master of Science

This thesis explores the dynamics of two bipedal, passive-walker models that are free to move in a three-dimensional environment. Specifically, two rigid-bodied walkers that can sustain anthropomorphic gait down an inclined plane with gravity being the only source of energy were studied using standard dynamical systems methods. This includes calculating the stability of periodic orbits and varying the system parameter to create bifurcation diagrams and to address the persistence of a periodic solution under specific parameter variations. These periodic orbits are found by implementing the Newton-Raphson root solving scheme. The dynamical systems associated with these periodic orbits are not completely smooth. Instead, they include discontinuities, such as those produced due to forces at foot contact points and during knee hyper-extension. These discontinuities are addressed in the stability calculations through appropriate discontinuity mappings. The difference between the two walker models is the number of degrees of freedom (DOF) at the hip. Humans possess three DOF at each hip joint, one DOF at each knee joint, and at least two DOF at each ankle joint. The first walker model studied had revolute joints at the hips and knees and completely locked ankles. To make the walking motion more anthropomorphic, additional degrees of freedom were added to the hip. Specifically, the second walker model has ball joints at the hips. Two control algorithms are used for controlling the local stability of periodic motions for both walker models. The methods, reference and delay feedback control, rely on the presence of discontinuities in the system. Moreover, it is possible to predict the effects of the control strategy based entirely on information from the uncontrolled system. Control is applied to both passive walker models to try and stabilize an unstable periodic gait by making small, discrete, changes in the foot orientation during gait. Results show that both methods are successful in stabilizing an unstable walking motion for a 3D model with one DOF in each hip and to reduce the instability of the walking motions for the model having more mobility in the hip joints. / Master of Science

Yes / Although gaze during adaptive gait involving obstacle crossing is typically directed two or more steps ahead, visual information of the swinging lower-limb and its relative position in the environment (termed visual exproprioception) is available in the lower visual field (lvf). This study determined exactly when lvf exproprioceptive information is utilised to control/update lead-limb swing trajectory during obstacle negotiation. 12 young participants negotiated an obstacle wearing smart-glass goggles which unpredictably occluded the lvf for certain periods during obstacle approach and crossing. Trials were also completed with lvf occluded for the entirety of the trial. When lvf was occluded throughout, footplacement distance and toe-clearance became significantly increased; which is consistent with previous work that likewise used continuous lvf occlusion. Both variables were similarly affected by lvf occlusion from instant of penultimate-step contact, but both were unaffected when lvf was occluded from instant of final-step contact. These findings suggest that lvf (exproprioceptive) input is typically used in an online manner to control/update final foot-placement, and that without such control, uncertainty regarding foot placement causes toe-clearance to be increased. Also that lvf input is not normally exploited in an online manner to update toe-clearance during crossing: which is contrary to what previous research has suggested.

No / We often complete step downs in the absence of visual feedback of the lower-limbs, and/or of the area on the ground where we intend to land (e.g. when descending a step whilst carrying a laundry basket). Therefore, the present study examined whether information from lower visual field (lvf) provides any advantage to the control of step descent. Ten healthy subjects (age 24.4 ± 9.4 years) completed repeated step downs over three-step heights with visual information available from either full or upper visual fields (lvf occluded), and for specific intervals relative to step initiation. Visuomotor control of step descent was assessed by determining pre-landing kinematic measures and landing mechanic variables for the initial landing period. Findings indicate that whilst there were only limited effects on pre-landing kinematic measures under lvf occlusion, individual’s ability to plan/control landing mechanics was significantly different in such conditions compared to when they had access to full field vision. These changes were consistent with participants being uncertain regarding precise floor height when access to lvf was restricted, and consequently led them to adapt their landing behaviour but without fundamentally altering their stepping strategy. Compared to when vision was available throughout, the occlusion of vision (full or upper visual field) from toe-off or mid-swing onwards caused very few differences in landing behaviour. This suggests that the contribution of information from lvf to the control of landing behaviour occurs predominantly prior to or during movement initiation and that ‘online’ vision is used only in the latter portion of the descent phase to subtly ‘fine tune’ landings.

This dissertation addresses the question, how and why do 'flying' snakes (Chrysopelea) undulate through the air? Instead of deploying paired wings or wing-like surfaces, flying snakes jump, splay their ribs into a bluff-body airfoil, and undulate through the air. Aerial undulation is the dominant feature of snake flight, but its effects on locomotor performance and stability are unknown. Chapter 2 describes a new non-equilibrium framework to analyze gliding animals and how the pitch angle affects their translational motion. Chapter 3 combines flying snake glide experiments and detailed dynamic modeling to address what is aerial undulation and how each kinematic component affects rotational stability and translational performance. Chapter 4 combines the kinematic data of Chapter 3, with elements of the non-equilibrium framework of Chapter 2, to examine the kinematics of snake flight in greater detail. This chapter also tests if our current understanding of flying snake aerodynamics is sufficient to explain the observed center of mass motion. / Ph. D. / Flying snakes can move unlike any other flying or slithering animal. Flying snakes have evolved the ability to glide safely to the ground by undulating through the air. Flapping flyers, like birds, bats, and insects, move through the air using wings and powerful flight muscles. In contrast, gliding animals fall through the air, using gravity to increase their speed, and air resistance to produce lift and drag forces such that they move over the ground. Flying snakes glide by jumping, flattening their bodies (similar to a cobra hooding), and undulating through the air using an ‘S’-shaped body. This dissertation addresses the question, how and why do flying snakes undulate through the air? First, I describe a new mathematical analysis of gliding animals, which provides a framework to understand how an animal’s size and orientation to the oncoming airflow affect its glide performance. Second, I describe glide experiments where the bodies of flying snakes were measured as they flew through a large indoor glide arena. From these measurements, we quantified how the body bends in the horizontal and vertical directions. Next, I describe a detailed mathematical model used to test how the different body configurations we measured affect glide performance and flight stability. The model result indicate that flying snakes likely use aerial undulation to stabilize their rotational motion. Third, I tested if our current measurements of the lift and drag properties of flying snakes, based on the quasi-steady assumption, can account for the trajectories we recorded. The force analysis suggests that flying snakes produce more force than the quasi-steady assumption can account for, and that future work is needed to understand unsteady aerodynamic mechanisms relevant for snake flight.

In virtual worlds, designers often consider "real walking" to be the gold standard when it comes to locomotion, as shown by attempts to incorporate walking techniques within tasks. When real walking is not conceivable due to several different limitations of virtual interactions (space, hardware, tracking, etc.) a walking simulation technique is sometimes used. We call these moderate interaction fidelity techniques and based upon literature, we can speculate that they will often provide an inferior experience if compared to a technique of high or low fidelity. We believe that there is an uncanny valley which is formed if a diagram is created using interaction fidelity and user effectiveness. Finding more points on this graph would help to support claims we have made with our hypothesis. There are several studies done previously in the field of virtual reality, however a vast majority of them considered interaction fidelity as a single construct. We argue that interaction fidelity is more complex involving independent components, with each of those components having an effect of the actual effectiveness of an interface. In addition, the intention of the designer can also have influence on how effective an interface can be. In this study we are going to be doing a deeper look into devices which attempt to overcome the limitations of physical space which we will call semi-natural interfaces. Semi-natural interfaces are sometimes difficult to use at first due to mismatch of cues or possibly due to a lack of fidelity, but training has been shown to be beneficial to overcome this difficulty. As of today, designers have not yet found a fully general solution to walking in large virtual environments. / Master of Science / When a user enters a virtual world, they expect it to be as realistic as possible. They expect to be able to move around an interact with objects exactly how they would in real life. This expectation is, at times, met with dismay when there are limitations between what the user expects to be able to do and what is possible for the experience to achieve. The level of realism in a virtual world is something that we call fidelity, and this comes in different levels ranging from low to high. An interaction in virtual reality which is far from how you would make that same interaction in the real world is called a low fidelity technique and this can be compared to a standard game controller being used to move a character forward. On the other spectrum, a technique in virtual reality with high similarities to the real-world interaction is call high fidelity. An example of a high-fidelity technique would be similar to having a user physically walk from one point to another to move the virtual character. In several studies it has been said that both high fidelity and low fidelity techniques have a positive effect on users and they perform well using them, but if the fidelity of the technique falls in between, it will have a negative effect on user experience. The studies in this document test several different fidelity levels of techniques in an attempt to add evidence to the hypothesis that medium fidelity devices currently do not improve user experience and in fact, are creating a negative one.

Initier la marche vient naturellement pour tout être vivant qui se déplace. Malgré cette apparente facilité, cet acte nécessite une interaction complexe entre différentes régions du cerveau et la moelle épinière. Une de ces régions a été découverte dans le mésencéphale et a été identifiée il y a maintenant 50 ans comme la région locomotrice mésencéphalique. En effet, la stimulation électrique de cette région engendre de manière systématique l’initiation de la locomotion dans de nombreuses espèces animales. Malgré tout, la localisation anatomique précise et l’identification des populations neuronales de cette région sont un sujet de débat encore aujourd’hui. Dans notre projet, nous avons utilisé les outils optogénetiques accessibles chez la souris afin de stimuler spécifiquement les populations glutamatergiques ou cholinergiques des deux noyaux qui constituent la région locomotrice mésencéphalique, le noyau cunéiforme (CnF) et le noyau pedonculopontin (PPN). Nous avons découvert que nous ne pouvions initier la marche en stimulant seulement les neurones glutamatergiques du noyau cunéiforme, indiquant ainsi que ces neurones constituent le corrélat anatomique de la région locomotrice mésencéphalique. Étant donné l’intérêt clinique de la stimulation profonde chez des patients parkinsoniens, épileptiques ou médullaires, il paraît d’autant plus urgent de définir la localisation et les fonctions précises des populations neuronales contribuant à cette région fonctionnelle. / The act of initiating locomotion comes naturally to every living and moving the animal. Despite this apparent easiness, this act relies upon a complex neuronal interaction between brain regions and the spinal cord. One of those regions was found in the brainstem and has been identified 50 years ago as the mesencephalic locomotor region. Indeed, electrical stimulation of this region consistently leads to the initiation of locomotion in many species. However, the precise anatomical location and neuronal composition responsible for this effect on locomotion remained a matter of debate for years. Here, using neuronal specific optogenetic stimulation in mice, we stimulated either the glutamatergic or the cholinergic population in the two proposed nuclei that form the MLR (cuneiform and pedunculopontine nuclei, CnF and PPN). We simultaneously recorded kinematics and EMG activity and found that we could only reliably induce locomotion when stimulating the glutamatergic neurons of the CnF, therefore establishing those neurons as the correlates of the MLR. Considering that the MLR is being tested as a deep brain stimulation target for disease ranging from Parkinson to epilepsy and spinal cord injury, it seems even more urgent to ascertain precisely its anatomical location and physiological role.