This thesis assesses the link between action and cognition early in development. Thus the notion of an embodied cognition is investigated by tying together two levels of action control in the context of reaching in infancy: prospective motor control and executive functions. The ability to plan our actions is the inevitable foundation of reaching our goals. Thus actions can be stratified on different levels of control. There is the relatively low level of prospective motor control and the comparatively high level of cognitive control. Prospective motor control is concerned with goal-directed actions on the level of single movements and movement combinations of our body and ensures purposeful, coordinated movements, such as reaching for a cup of coffee. Cognitive control, in the context of this thesis more precisely referred to as executive functions, deals with goal-directed actions on the level of whole actions and action combinations and facilitates directedness towards mid- and long-term goals, such as finishing a doctoral thesis. Whereas prospective motor control and executive functions are well studied in adulthood, the early development of both is not sufficiently understood. This thesis comprises three empirical motion-tracking studies that shed light on prospective motor control and executive functions in infancy. Study I investigated the prospective motor control of current actions by having 14-month-olds lift objects of varying weights. In doing so, multi-cue integration was addressed by comparing the use of visual and non-visual information to non-visual information only. Study II examined the prospective motor control of future actions in action sequences by investigating reach-to-place actions in 14-month-olds. Thus the extent to which Fitts’ law can explain movement duration in infancy was addressed. Study III lifted prospective motor control to a higher that is cognitive level, by investigating it relative to executive functions in 18-months-olds. Main results were that 14-month-olds are able to prospectively control their manual actions based on object weight. In this action planning process, infants use different sources of information. Beyond this ability to prospectively control their current action, 14-month-olds also take future actions into account and plan their actions based on the difficulty of the subsequent action in action sequences. In 18-month-olds, prospective motor control in manual actions, such as reaching, is related to early executive functions, as demonstrated for behavioral prohibition and working memory. These findings are consistent with the idea that executive functions derive from prospective motor control. I suggest that executive functions could be grounded in the development of motor control. In other words, early executive functions should be seen as embodied.

"Patient motion, which causes artifacts in reconstructed images, can be a serious problem in Single Photon Emission Computed Tomography (SPECT) imaging. If patient motion can be detected and quantified, the reconstruction algorithm can compensate for the motion. A real-time multi-threaded Visual Tracking System (VTS) using optical cameras, which will be suitable for deployment in clinical trials, is under development. The VTS tracks patients using multiple video images and image processing techniques, calculating patient motion in three-dimensional space. This research aimed to develop and implement an algorithm for feature matching and stereo location computation using multiple cameras. Feature matching is done based on the epipolar geometry constraints for a pair of images and extended to the multiple view case with an iterative algorithm. Stereo locations of the matches are then computed using sum of squared distances from the projected 3D lines in SPECT coordinates as the error metric. This information from the VTS, when coupled with motion assessment from the emission data itself, can provide a robust compensation for patient motion as part of reconstruction."

Natural human motion is highly demanded and widely used in a variety of applications such as video games and virtual realities. However, acquisition of full-body motion remains challenging because the system must be capable of accurately capturing a wide variety of human actions and does not require a considerable amount of time and skill to assemble. For instance, commercial optical motion capture systems such as Vicon can capture human motion with high accuracy and resolution while they often require post-processing by experts, which is time-consuming and costly. Microsoft Kinect, despite its high popularity and wide applications, does not provide accurate reconstruction of complex movements when significant occlusions occur. This dissertation explores two different approaches that accurately reconstruct full-body human motion from noisy and ambiguous input data captured by commercial motion capture devices. The first approach automatically generates high-quality human motion from noisy data obtained from commercial optical motion capture systems, eliminating the need for post-processing. The second approach accurately captures a wide variety of human motion even under significant occlusions by using color/depth data captured by a single Kinect camera. The common theme that underlies two approaches is the use of prior knowledge embedded in pre-recorded motion capture database to reduce the reconstruction ambiguity caused by noisy and ambiguous input and constrain the solution to lie in the natural motion space. More specifically, the first approach constructs a series of spatial-temporal filter bases from pre-captured human motion data and employs them along with robust statistics techniques to filter noisy motion data corrupted by noise/outliers. The second approach formulates the problem in a Maximum a Posterior (MAP) framework and generates the most likely pose which explains the observations as well as consistent with the patterns embedded in the pre-recorded motion capture database. We demonstrate the effectiveness of our approaches through extensive numerical evaluations on synthetic data and comparisons against results created by commercial motion capture systems. The first approach can effectively denoise a wide variety of noisy motion data, including walking, running, jumping and swimming while the second approach is shown to be capable of accurately reconstructing a wider range of motions compared with Microsoft Kinect.

Οι καρδιαγγειακές παθήσεις αποτελούν σήμερα την πρώτη αιτία θανάτου στις αναπτυγμένες χώρες. Οι αιτίες που τις προκαλούν συνδέονται πολύ συχνά με τις ιδιότητες και την γενική κατάσταση των τοιχωμάτων των μεγάλων αρτηριών. Η υπερηχητική απεικόνιση των τελευταίων είναι εξαιρετικά σημαντική για τη διάγνωση πιθανών παθολογικών καταστάσεων, καθώς χαρακτηρίζεται από χαμηλό κόστος και ελάχιστη επιβάρυνση για τον οργανισμό του ασθενούς, ενώ μπορεί να πραγματοποιείται σε πραγματικό χρόνο. Επιπλέον, οι υπερηχητικές τεχνικές απεικόνισης επιτρέπουν την παρακολούθηση της κίνησης των αρτηριακών τοιχωμάτων, από την οποία μπορούν να εξαχθούν αρκετά ασφαλή συμπεράσματα για την κατάστασή τους. Για την παρακολούθηση της κίνησης των αρτηριακών τοιχωμάτων έχουν χρησιμοποιηθεί διάφορες μέθοδοι, με κυριότερες αυτές που βασίζονται στο φαινόμενο Doppler (Tissue Doppler Imaging), τις διαφορικές μεθόδους οπτικής ροής και τις μεθόδους ταύτισης περιοχών (block matching). Οι μέθοδοι Doppler είναι εξαιρετικά ακριβείς, μόνο όμως κοντά στη διεύθυνση της υπερηχητικής δέσμης. Οι μέθοδοι οπτικής ροής μπορούν να χρησιμοποιηθούν σε διδιάστατες απεικονίσεις με αρκετά ικανοποιητική ακρίβεια, αδυνατούν ωστόσο να παρακολουθήσουν μεγάλες μετατοπίσεις. Από την άλλη πλευρά, οι μέθοδοι ταύτισης περιοχών δεν παρουσιάζουν τα παραπάνω προβλήματα, υστερούν όμως σε ακρίβεια. Μια σχετικά νέα τεχνική με ευρεία εφαρμογή στην ιατρική απεικόνιση είναι τα ενεργά περιγράμματα (active contours). Πρόκειται για παραμετρικές καμπύλες που κινούνται στο επίπεδο της εικόνας έτσι ώστε να ελαχιστοποιείται ένα ενεργειακό συναρτησιακό και επιτρέπουν την ανίχνευση αντικειμένων στην εικόνα. Στις κλασικές μεθόδους των ενεργών περιγραμμάτων, η αρχική καμπύλη πρέπει να ορίζεται κοντά στο προς ανίχνευση αντικείμενο. Για την αντιμετώπιση του προβλήματος αυτού έχουν προταθεί διάφορες βελτιώσεις του κλασικού μοντέλου των ενεργών περιγραμμάτων, όπως η εισαγωγή της λεγόμενης «δύναμης μπαλονιού». Τα ενεργά περιγράμματα μπορούν να χρησιμοποιηθούν και για παρακολούθηση κίνησης σε ακολουθίες εικόνων, καθώς μπορούν να προσαρμόζονται στα εξέχοντα χαρακτηριστικά των κινούμενων δομών. Ωστόσο, στην υπερηχητική απεικόνιση των αρτηριακών τοιχωμάτων, η περιπλοκότητα της κίνησής τους και ο έντονος θόρυβος καθιστούν ιδιαίτερα δύσκολη την άμεση εφαρμογή των ενεργών περιγραμμάτων για την παρακολούθηση κίνησης. Στόχος της παρούσας εργασίας είναι ο συνδυασμός των ενεργών περιγραμμάτων και των μεθόδων ταύτισης περιοχών για την αυτοματοποίηση της παρακολούθησης κίνησης σε ακολουθίες εικόνων των τοιχωμάτων αρτηριών (συγκεκριμένα της καρωτιδικής και της βραχιακής) και για τη βελτίωση της επαναληψιμότητας των σχετικών μετρήσεων. Αρχικά, εφαρμόστηκαν οι μέθοδοι ταύτισης περιοχών ενός επιπέδου (Single Level Block Matching) και πολλών επιπέδων (Multilevel Block Matching) για την παρακολούθηση της κίνησης των αρτηριακών τοιχωμάτων από ακολουθίες εγκάρσιων τομών της καρωτιδικής και της βραχιακής αρτηρίας. Μια κλειστή καμπύλη ορίστηκε από το χρήστη στο πρώτο πλαίσιο της ακολουθίας, έτσι ώστε να αντιστοιχεί κατά προσέγγιση στο περίγραμμα των ορίων του αρτηριακού τοιχώματος και καταγράφηκε η επιφάνεια που περικλείεται από την καμπύλη αυτή κατά τη διάρκεια ενός καρδιακού κύκλου. Η μετατόπιση των σημείων της καμπύλης από πλαίσιο σε πλαίσιο εκτιμήθηκε με τις μεθόδους ταύτισης περιοχών. Η μορφή της γραφικής παράστασης της επιφάνειας αυτής σε συνάρτηση με το χρόνο (δηλαδή τον αριθμό του πλαισίου) αποτελεί έναν πολύ καλό δείκτη της κατάστασης της αρτηρίας. Η αυτοματοποίηση της διαδικασίας λήψης των παραπάνω μετρήσεων μπορεί να επιτευχθεί αν η επιλογή της αρχικής κλειστής καμπύλης δεν βασίζεται στην εκτίμηση του χρήστη αλλά στην ανίχνευση των τοιχωμάτων με ενεργά περιγράμματα. Το κλασικό μοντέλο των ενεργών περιγραμμάτων και το μοντέλο της «δύναμης μπαλονιού» εφαρμόστηκαν για αυτό το σκοπό στο πρώτο πλαίσιο των ακολουθιών εικόνων των αρτηριών. Διαπιστώθηκε ότι το μοντέλο της δύναμης μπαλονιού δίνει ικανοποιητικά αποτελέσματα ανίχνευσης των αρτηριακών τοιχωμάτων και μάλιστα με ικανοποιητική επαναληψιμότητα, καθώς το αποτέλεσμα της ανίχνευσης δεν διαφοροποιούνταν σημαντικά από την επιλογή της αρχικής κλειστής καμπύλης του ενεργού περιγράμματος, αρκεί η ακτίνα της τελευταίας να είναι τέτοια ώστε η καμπύλη να βρίσκεται εξ ολοκλήρου στο εσωτερικό της αρτηρίας. Στη συνέχεια, η καμπύλη που προέκυψε από την ανίχνευση των τοιχωμάτων χρησιμοποιήθηκε ως αρχική καμπύλη για την παρακολούθηση κίνησης με τις μεθόδους ταύτισης περιοχών. Τα αποτελέσματα που προέκυψαν δεν διαφέρουν σημαντικά σε σχέση με την περίπτωση όπου ο ορισμός της καμπύλης στο πρώτο πλαίσιο γίνεται από το χρήστη. Συνεπώς, η ανίχνευση των αρτηριακών τοιχωμάτων με ενεργά περιγράμματα μπορεί να χρησιμοποιηθεί για να βελτιώσει την επαναληψιμότητα των μετρήσεων για την παρακολούθηση κίνησης και να συμβάλει στην αυτοματοποίηση της διαδικασίας λήψης τους. / Cardiovascular diseases are the leading cause of death today in developed countries. Their causes are very frequently related with the status of artery walls. Ultrasonic imaging is very important for the diagnosis of possible arterial pathology, because it is of low cost, safe for the patient and can be performed in real time. Ultrasonic imaging also allows arterial wall motion tracking, which can provide critical diagnostic information. Motion tracking methods include Tissue Doppler Imaging (TDI), differential optical flow methods and block matching. Tissue Doppler Imaging offers excellent accuracy, restricted however to directions close to the direction of the ultrasonic beam. Optical flow methods can be used in two dimensions with considerable accuracy, but they fail in cases of fast moving structures. In the case of block matching, no such problems have to be dealt with, however with significant cost in accuracy. Active contours, a relatively new technique widely used in medical imaging, are parameterized curves moving on the image plane in order to minimize an energy functional and allowing object detection. Classical active contour methods require that the initial curve of the model is defined close to the object to be detected. In order to avoid this, several techniques have been proposed, such as the so-called “balloon force”. Active contours can also be used for motion tracking in series of image frames, provided that they can fit to salient features of moving structures. In arterial wall ultrasonic imaging however, motion complexity and noise obstruct motion tracking with active contours. In the current study active contours and block matching methods are combined to improve reproducibility of motion tracking measurements in series of artery wall images (namely for the carotid and brachial artery). Single level and multilevel block matching methods were used for artery wall motion tracking. A closed curve was defined by the user in the first frame of the image series, both for the carotid and brachial artery. This curve is a rough estimation of the arterial wall contour. The area enclosed by the curve is recorded throughout a cardiac cycle. Curve movement is estimated with block matching methods. The graph pattern of enclosed area versus time (i.e. frame number) is a very good indicator for the status of the artery. The above process can be automatized if the initial closed curve is produced by object detection with active contours and not by estimation. The active contours classical model and the balloon force model were used for artery wall detection in the first frame of the artery image series. The balloon force model yielded satisfactory wall detection results with considerable reproducibility. The choice of the dimensions of the initial contour of the model did not affect the final result considerably, provided that the initial contour is fully placed inside the arterial lumen. The curve that resulted from object detection was used to initialize the motion tracking process with block matching methods. In this way, similar motion tracking results can be obtained for the artery image series, but with much improved reproducibility.

Container vessel motions need to be small when loading and offloading cargo while moored to wharfs. Waves and their reflections from structures can induce ship motions. These motions are characterized by six degrees of freedom, including translations of surge, sway, and heave and rotations of pitch, roll, and yaw. Monitoring and quantifying these motions offer a reference for design and selection of the mooring system and wharf types. To measure the six degrees of freedom motions of a container ship moored to a dock, a 1:50 scale model is moored to two types of dock, solid wall dock and pile supported dock. Irregular waves of TMA spectrum with various periods, heights, and directions are generated in the wave basin to induce the motions of the model container ship. Optical motion capturing cameras are used to measure and quantify the six degree of freedom motions. Results of the effects of wave period, significant wave height, and wave direction on the motion characteristics of the model container ship moored at the solid dock and a pile supported dock are described in detail. A numerical simulation called aNySIM is applied to numerically predict the motion characteristics of the container ship moored to a solid wall dock only. The physical model experimental results of solid dock are also compared with the numerical simulation. These comparisons indicate that the motion characteristics of the model container ship represent similar trends for both rotations and translations. The experimental and numerical prediction values of motions of the ship moored to a solid wall dock display the same tendencies while differing in magnitude.

A realtime wireless motion tracking system is developed. The system is capable of tracking the orientations of multiple wireless sensors, using a semi-distributed implementation to reduce network bandwidth and latency, to produce real-time animation of rigid body models, such as the human skeleton. The system has been demonstrated to be capable of full-body posture tracking of a human subject using fifteen devices communicating with a basestation over a single, low bandwidth, radio channel. The thesis covers the theory, design, and implementation of the tracking platform, the evaluation of the platform’s performance, and presents a summary of possible future applications.

The recent leaps in virtual reality (VR) technology have unleashed revolutionary potential for applications in a wide variety of areas, including education, training, psychological-therapy, etc. As part of the effort on understanding how users interact with VR, I focused on studying full-body joint action using a road crossing task which involves perception, decision-making, action, and joint action. I have been heavily involved in the design, implementation, and construction of two large-screen, room-like stereoscopic virtual environment (VE) simulators. Using this system, I developed a three-part research plan with a series of studies to examine how people engage in full-body joint-action with a partner under three scenarios: 1. two people who are physically present in a co-occupied virtual environment; 2. one person who shares a virtual environment with a computer-generated agent (CG agent); 3. two people who share the same virtual environment remotely in physically separate places where each person is motion tracked and presented in the environment as a graphic avatar. The behaviors of participants were recorded and processed through a customized pipeline that captures important performance metrics, such as how participants pick crossable gaps and time their movements. The VE system, user study designs, and findings are introduced in this dissertation.

The modern office environment requires employees to perform stationary work. This can cause them several health issues due to being sedentary for long periods of time. An exergame was developed with the aim to remedy these issues by encouraging short motion controlled game sessions during breaks. The game was a farming game developed using the Godot game engine and the ML based skeletal tracking software Mediapipe. The game was played for 86 two-minute sessions where data was collected to evaluate how to use farming game tropes within the design for more movement to yield better results. It was also used to evaluate how the game mechanics could be distributed throughout the game session to promote sustained exertion during an average session. It was concluded that for farming exergames, if the goal is to reward players who exert themselves more, the in-game rewards should not make the game easier to play effectively as they generally do in typical farming games. Furthermore, it was also concluded that interactions happening in a sporadic order help with keeping the average exertion consistent, in addition to the aspect that players always have something to do during the allotted game session time.

While lumbar kinematics can be measured in vivo, most measurements are invasive (such as percutaneous bone pins), provide high doses of radiation (such as biplane fluoroscopy), or are taken with the patient in a static position (such as MRIs). Recent work suggests that lumbar kinematics can be determined by dynamic measurements of epidermal strain in the lower back. This work aims to develop and examine a method of examining lumbar kinematics via optoelectronic motion capture utilizing skin-mounted markers in the lumbar region. Two studies were performed. One study examined lumbar epidermal strain in 28 asymptomatic subjects during diagnostic movements, while the second study used fresh/frozen cadavers to compare segmental lumbar kinematics as measured by both an optoelectronic motion capture system utilizing skin-mounted markers and an electromagnetic motion capture system utilizing sensors mounted to percutaneous bone pins inserted into the spinous processes. In the first study, participants had a grid-like marker set adhered to their lower back. They were instructed to perform 17 diagnostic movements, with data from three trials of each exercise being captured. Data was analyzed in MATLAB to examine segmental lumbar kinematics. Analysis shows trends consistent with expected movement patterns for asymptomatic individuals with measurement values consistent with those found in previous studies. Trends of symmetry in motion for left versus right motions were observed, as well as a trend for the return motion in a movement to be faster than the outgoing motion. In the second study, three fresh/frozen cadavers were outfitted with electromagnetic motion tracking sensors mounted to bone pins which were placed in the spinous processes of L1-S2. Each cadaver also had a similar grid-like marker set of optical motion tracking markers adhered in the lumbar region. The cadavers were moved through 10 of the same diagnostic exercises with data from seven trials from each exercise being captured. Data was analyzed in MATLAB to compare the end range of motion as measured by the optical system to the same measurements by the electromagnetic system. End ROM values showed statistically different measurements for five of the twelve segment measurements compared. Data collected in this work contributes to the establishment of normative dynamic kinematics of the lumbar spine in the asymptomatic population. It also outlines the strengths and weaknesses of the methodology utilized.

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