Target Acquisition in Multiscale Electronic Worlds

Since the advent of graphical user interfaces, electronic information has grown exponentially, whereas the size of screen displays has stayed almost the same. Multiscale interfaces were designed to address this mismatch, allowing users to adjust the scale at which they interact with information objects. Although the technology has progressed quickly, the theory has lagged behind. Multiscale interfaces pose a stimulating theoretical challenge, reformulating the classic target-acquisition problem from the physical world into an infinitely rescalable electronic world. We address this challenge by extending Fitts’ original pointing paradigm: we introduce the scale variable, thus defining a multiscale pointing paradigm. This article reports on our theoretical and empirical results. We show that target-acquisition performance in a zooming interface must obey Fitts’ law, and more specifically, that target-acquisition time must be proportional to the index of difficulty. Moreover, we complement Fitts’ law by accounting for the effect of view size on pointing performance, showing that performance bandwidth is proportional to view size, up to a ceiling effect. The first empirical study shows that Fitts’ law does apply to a zoomable interface for indices of difficulty up to and beyond 30 bits, whereas classical Fitts’ law studies have been confined in the 2-10 bit range. The second study demonstrates a strong interaction between view size and task difficulty for multiscale pointing, and shows a surprisingly low ceiling. We conclude with implications of these findings for the design of multiscale user interfaces

Espace et échelle du mouvement : la loi de Fitts dans le monde physique et dans les mondes électroniques

Nous avons conçu et mis en oeuvre une approche nouvelle du paradigme classique du pointage faisant jouer un rôle central à la variable d’échelle. Nous utilisons le diagramme espace-échelle introduit par Furnas et Bederson (1995) dans le champ de l’interaction homme-machine (IHM). Fondé sur une géométrie inédite, ce type de représentation permet de visualiser les variations d’échelle en même temps que les déplacements dans l’espace, ce qui nous a permis d’analyser la cinématique de la navigation au sein des mondes électroniques multi-échelle (ou zoomables). Les travaux rapportés dans ce document se développent autour de la frontière qui sépare le monde réel et les mondes d’information. Le monde réel dans lequel s’inscrivent normalement nos mouvements est typiquement dynamique : il met en jeu la masse, la longueur et le temps. En revanche, les mondes d’information auxquels les humains sont exposés depuis à peine deux décennies sont d’essence purement cinématique, en ce sens qu’ils ignorent typiquement la masse, et donc les contraintes de force, d’énergie et de puissance. C’est la nature cinématique des mondes d’information qui explique que leurs contenus soient indéfiniment rescalables, propriété dont les objets du monde physique ne jouissent que dans une étroite mesure, comme on le sait depuis Galilée

Neurophysiological Responses to Rest and Fatiguing Exercise in Severe Hypoxia in Healthy Humans

The central nervous system is highly sensitive to reductions in oxygen availability but the neurophysiological responses in healthy human lowlanders are not well understood. In severe hypoxia, whole-body exercise tolerance is impaired and neuromuscular fatigue, defined as any exercise-induced reduction in the ability of a muscle to generate force or power, reversible by rest, may be largely due to cerebral perturbations. The primary aim of this thesis was to determine the mechanisms of exercise-induced neuromuscular fatigue and the related neurophysiological responses to acute, chronic and intermittent severe hypoxia in healthy humans. In acute severe hypoxia (AH), exercise tolerance was, in part, mediated by a hypoxia-sensitive source of central fatigue, measured as a decrease in voluntary activation (VA) of the knee extensors (Study 1 – 4). This coincided with a significant challenge to systemic (arterial oxygen saturation [SpO2] ≈ 70%, Study 1 - 4) and cerebral oxygen availability at end-exercise (Study 3 - 4). The rate of development of peripheral locomotor muscle fatigue was blunted at task failure in AH in comparison to normoxia (Study 1 – 2). Corticospinal excitability and the neuromuscular mechanisms of fatigue were measured after a prolonged (two-week) exposure to high altitude in Study 3 (5260 m above sea level, Mount Chacaltaya, Bolivia). This was the first study to show that acclimatisation to chronic severe hypoxia (CH) alleviates the development of supraspinal fatigue induced by whole-body exercise in AH. This occurred in parallel to an improved cerebral oxygen delivery and cerebral oxygenation. Interestingly, the neurophysiological responses at rest in CH were characterised by an increased corticospinal and muscle membrane excitability. The peripheral contribution to neuromuscular fatigue was not attenuated following acclimatisation to high altitude. In study 4, a two-week protocol of intermittent hypoxia (IH) attenuated exercise-induced supraspinal fatigue measured in AH and substantially improved constant-power cycling in severe hypoxia. Total haemoglobin mass was unaltered by IH, but arterial oxygen content was improved due to an increase in SpO2, secondary to an enhanced ventilatory response to exercise. Peripheral locomotor muscle fatigue was lower following IH, which may be related to exercise training in hypoxia. Although corticospinal excitability was unchanged following a single 2-h exposure to severe hypoxia, repeated exposures of IH resulted in a transient increase in motor cortex excitability without changes in intracortical inhibition. (Study 5). In conclusion, in acute severe hypoxia, whole-body exercise tolerance is impaired through oxygensensitive mechanisms which exacerbate central fatigue. The acute response can be alleviated following both chronic and intermittent severe hypoxia

Una aproximación dinámica y ecológica a las escalas de adaptación del comportamiento

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Psicología. Fecha de lectura: 31-03-201

Perceptual and Attentional Constraints on 1:1 Bimanual Coordination

Two experiments were conducted in an attempt to further the understanding of how previously identified intrinsic constraints and perceptual factors interact in influencing the learning and performance of various bimanual coordination patterns. The purpose of Experiment 1 was to determine the influence of Lissajous feedback on 1:1 bimanual coordination patterns (0°, 90°, 180° phase lags) when the movement amplitudes of the two limbs were different. Participants coordinated rhythmic movements of their forearms while being provided separate feedback for each limb (no- Lissajous group) or integrated feedback (Lissajous group). Data from Experiment 1 supports the notion that the lead-lag relationship as well as amplitude assimilation between limbs observed in the literature can be partially attributed to the visualperceptual factors present in the testing environment. When participants are provided integrated feedback in the form of Lissajous plots and templates much of the lead-lag and amplitude assimilation effects were eliminated and relative phase error and variability were also greatly reduced after only 3 min of practice under each condition. Results from recent experiments suggest that when the salient visual information (Lissajous feedback) is removed, performance in bimanual coordination tasks rapidly deteriorates. The purpose of Experiment 2 was to determine if reducing the frequency of feedback presentation will decrease the reliance on the feedback and will facilitate the development of an internal representation that will improve performance when visual feedback is removed. Participants receiving reduced frequency feedback presentation were able to perform a delayed retention test with the feedback removed as well as the test with feedback present. Data from Experiment 2 demonstrates that salient extrinsic Lissajous feedback can effectively be combined with reduced frequency feedback presentation in a way that performance levels, when tested without the availability of feedback, match those obtained when tested in the presence of Lissajous feedback. Taken together the present experiments add to the growing literature that supports the notion that salient perceptual information can override some aspects of the system's intrinsic dynamics typically linked to motor output control. The strong tendencies toward the intrinsic dynamics found in numerous previous bimanual movement studies and the difficulties in producing various coordination patterns may actually represent detrimental effects attributable to the perceptual information available in the environment and the attentional focus participants adopt. Given external integrated salient visual information participants can essentially tune-in and learn difficult bimanual coordination patterns with relatively little practice

Neuromuscular adaptations during long-term bed rest

The weightless environment encountered during human spaceflight virtually eliminates the mechanical loading of the human body. The accompanying physical inactivity sets in motion a cascade of changes that affects practically every physiological system in the human body. Of particular medical and operational concern are the decrements in skeletal muscle strength (force, power and endurance capacity) of the legs and the demineralization of weight- bearing bones. By now, it is acknowledged that these functional impairments may be prevented by adequate muscle exercise. This thesis addresses the study into the neuromuscular adaptations in the quadriceps femoris muscle as a consequence of bed rest-induced physical inactivity. Bed rest is hereby used as a simulation model of human spaceflight. The nature and progression of the adaptations, but also the preventative effect of physical were studied. In the Berlin bed rest study, the used training paradigm comprised combined resistance and vibration exercise, i.e. strength training exercises were performed against a mechanically vibrated platform. We were interested in the changes that occur during – particularly in the early stage of – bed rest. Hence, besides conducting experiments pre- and post bed rest, we also performed seven experiments – with an increasing time interval between experiments - during the eight weeks of bed rest. To disentangle the neural activation of the muscle from more intrinsic muscle characteristics both voluntary and electrically stimulated contractions were assessed. Voluntary motor control was assessed using two procedures: by means of superimposed electrical stimulation and by means of recording the electrophysiological properties of the quadriceps muscle by means of a sophisticated high-density surface electromyography methodology (HD-sEMG). The results of the studies described in this thesis have contributed to a better understanding of the underlying mechanisms and the time course in which they contribute to the various manifestations of muscle weakness as a result of physical inactivity imposed by strict bed rest. Most notably were the findings of a linear reduction in voluntary isometric knee extension strength, and an increase in relative muscle fatigability. These adaptations were predominantly the result of a linear decay in the cross- sectional area of the quadriceps femoris muscle and a reduced blood flow as a consequence of bed rest. Changes in the intrinsic contractile characteristics of the quadriceps femoris towards a faster muscle also progressed linearly in time. An unexpected finding across experiments was that the adopted longitudinal study fully prevented neural deconditioning. Vigorous resistive vibration exercise training during bed rest appeared a suitable gravity-independent countermeasure that offset or substantially mitigated most of the adaptive changes in quadriceps femoris muscle that evolved during bed rest in the absence of this countermeasure.Haan, A. [Promotor]de Stegeman, D.F. [Promotor]Gerrits, H.L. [Copromotor

Impact of fatiguing exercise on corticospinal excitability and motor performance in young and older adults

The impact of fatigue on corticospinal excitability and GABAergic inhibitory activity has been relatively well studied in young adults. However, this is yet to be established in older adults. Furthermore, the role of fatigue on motor skill performance remains largely understudied with a majority of the studies ranging between the 1970s-90s in young adults. The purpose of this thesis was to identify the age-related differences in corticospinal mechanisms and motor performance with isometric single joint fatiguing exercise. This was achieved by applying single and paired-pulse transcranial magnetic stimulation (TMS) prior to, during, and after exercise, as well as performance of a speed-accuracy movement task in both age groups. The first experimental study (chapter two) evaluated the effect of fatigue induced by a fifteen-minute sustained submaximal isometric contraction (15% of maximum electromyography [EMG]) of the first dorsal interosseous (FDI) muscle on corticospinal excitability, short- (SICI) and long- (LICI) interval intracortical inhibition in young and older adults. While no change in SICI was identified in both age groups, an age-related reduction in amount of LICI was seen suggesting a compensatory decline in GABAB mediated inhibition in older adults. Nevertheless, a varying magnitude of fatigue was observed between young and old which required further investigation. The second experimental study (chapter three) implemented a larger muscle group (elbow flexor muscles) and a submaximal isometric contraction held at 30% of their maximum force to task failure to achieve a similar amount of fatigue in both age groups. Contrary to chapter two, an identical decline in GABAB mediated inhibition was observed in both age groups when a similar amount of fatigue was induced, indicating that fatigue related changes in GABA modulation may be task and muscle dependent. Using a similar exercise model, the third experimental study (chapter four) investigated age-related differences in performance of a speed-accuracy task with fatigue. While there was an attenuation in motor skill performance with increasing task difficulty, there were no differences across age groups. Given the noted impact of fatigue on corticospinal excitability and motor performance in chapters two, three and four, investigation of transcranial direct current stimulation (tDCS) as a possible intervention was assessed as the final step. TDCS can be used to manipulate fatigability either as a priming tool or in conjunction with a fatiguing task. In the final study (chapter five), the impact of cathodal primed anodal tDCS on corticospinal excitability, fatigability, and motor skill performance was assessed in both age groups with an unexpected suppression in corticospinal excitability and greater attenuation in GABAB observed following anodal tDCS. However, cathodal priming as standalone had no direct impact on corticospinal excitability, GABA modulation, fatigability, or motor skill performance. This thesis provides novel evidence of an age-related retention in the ability to modulate corticospinal excitability and motor performance when a similar amount of fatigue is induced in young and older adults.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 202