Thesis (doctoral)--Universität Leipzig. / Vita.

No description available.

The interactions between illusory and real contours have been inves- tigated under monocular, binocular and dichoptic conditions. Results show that under all three presentation conditions, periodic alternations, generally called rivalry, occur during the perception of cognitive (or illusory) triangles, while earlier research had failed to find such rivalry (Bradley & Dumais, 1975). With line triangles, rivalry is experienced only under dichoptic conditions. A model is proposed to account for the observed phenomena, and the results of simulations are presented.

Job rotation is recommended to prevent musculoskeletal disorders (MSD). The premise is by involving different tissues a “working rest” for other tissues is created. The possible health benefits from this relief have not been investigated with regards to different grips in hand intensive jobs. The purpose of this study is to investigate hand intensive tasks and determine whether rotating between the power grip and lateral pinch grip can provide a benefit. A psychophysical load adjustment protocol was used. To investigate the effect of rotation, three different trials were collected. These included: power grip only, lateral pinch only, and alternating the two grips. Each trial was 60 minutes in duration, with a 12second cycle time, and 25% duty cycle. Fourteen subjects were recruited and pre-screened for any upper extremity disorders. Subjects were instructed to “work as hard as you can without straining your hand, wrist or forearm”; by adjusting their resistance settings to achieve a maximum acceptable force (MAF). Grip forces were exerted on an adjustable system using a hand grip dynamometer. Ratings of perceived discomfort were reported every 10minutes. Electromyography (EMG) was collected on eight forearm muscles during the combination trial. The demand for both lateral pinch and power grip tasks were at self selected levels and no fatigue was reported within MAF, EMG recordings, and discomfort reports. The rotation between lateral pinch and power grip had no apparent effect on MAF. However, EMG data hinted that there was a rotation of activation between first dorsal interossei and the forearm flexors (not statistically significant). Less discomfort was reported within the combination trial than the single grip (not significant). The study found no measurable difference in MAF when rotating between the power grip and lateral pinch. Considering there was no increase in demand, there is potential benefit to rotation, with trends to rotating activation between muscles, less discomfort being reported, and a general preference for the rotation. Given the high rates of MSD, and rotation being an effective tool to lower exposure, further investigations are required to understand relationships between similar muscles groups within hand intensive work environments.

Flies use visual cues for a variety of tasks, such as maneuvering through the environment and finding potential mates. Hoverflies, in particular, have very developed eyes and use them to be able to hover mid air and perform fast, elegant movements. The Motion Vision Group, located at the Department of Neuroscience at BMC, Uppsala, studies the motion vision system of the hoverfly brain, using electrophysiology. Experiments are performed by displaying visual stimuli on a screen in front of an immobilized fly, while recording the response from a single neuron with a thin electrode.Until now, the Motion Vision group has been using the open source program VisionEgg to generate the stimuli. VisionEgg is able to display stimuli at high frame rate and has a large set of useful features such as perspective distortion. It also has a lot of drawbacks that makes it desirable to acquire new software. The main drawbacks include it being hard to learn, use and modify, as well as being unable to generate the stimuli needed for some key experiments.This master´s thesis describes the development of software more suited to the lab´s needs. This software should be able to generate some of the stimuli that were impossible to do at the moment, as well as being easy to expand and add upon. The frame rate of the displayed stimuli has to be both high and stable in order to perform high precision experiments.The resulting program is called FlyFly and has been developed iteratively in close cooperation with its end users, ensuring a user friendly end product capable of meeting the lab´s needs. FlyFly is implemented using MatLab and the Psychophysics toolbox with the graphical user interface (GUI) designed with the Guide editor. The GUI is decoupled from the functions drawing the stimuli, making it easy to improve or remove parts altogether. FlyFly is intuitive to use and allows anyone to quickly get started. It allows easy manipulation of series of trials, and supports drawing of multiple objects simultaneously. With the current machine set-up, it displays stimuli at 160 frames per second with few or no dropped frames.FlyFly is currently being used in the lab and will be so for the foreseeable future.

Job rotation is recommended to prevent musculoskeletal disorders (MSD). The premise is by involving different tissues a “working rest” for other tissues is created. The possible health benefits from this relief have not been investigated with regards to different grips in hand intensive jobs. The purpose of this study is to investigate hand intensive tasks and determine whether rotating between the power grip and lateral pinch grip can provide a benefit. A psychophysical load adjustment protocol was used. To investigate the effect of rotation, three different trials were collected. These included: power grip only, lateral pinch only, and alternating the two grips. Each trial was 60 minutes in duration, with a 12second cycle time, and 25% duty cycle. Fourteen subjects were recruited and pre-screened for any upper extremity disorders. Subjects were instructed to “work as hard as you can without straining your hand, wrist or forearm”; by adjusting their resistance settings to achieve a maximum acceptable force (MAF). Grip forces were exerted on an adjustable system using a hand grip dynamometer. Ratings of perceived discomfort were reported every 10minutes. Electromyography (EMG) was collected on eight forearm muscles during the combination trial. The demand for both lateral pinch and power grip tasks were at self selected levels and no fatigue was reported within MAF, EMG recordings, and discomfort reports. The rotation between lateral pinch and power grip had no apparent effect on MAF. However, EMG data hinted that there was a rotation of activation between first dorsal interossei and the forearm flexors (not statistically significant). Less discomfort was reported within the combination trial than the single grip (not significant). The study found no measurable difference in MAF when rotating between the power grip and lateral pinch. Considering there was no increase in demand, there is potential benefit to rotation, with trends to rotating activation between muscles, less discomfort being reported, and a general preference for the rotation. Given the high rates of MSD, and rotation being an effective tool to lower exposure, further investigations are required to understand relationships between similar muscles groups within hand intensive work environments.

Maximum voluntary forces and psychophysically acceptable forces are often used to set force guidelines for exertions as a means to protect against overexertion injuries in the workplace. The focus of this dissertation was the exploration of the roles of whole body balance, shoe-floor friction and joint strength in limiting the capacity of a person to produce maximum voluntary hand forces and psychophysically acceptable hand forces. The underlying goal was to advance knowledge regarding how physical exertion capacity is biomechanically governed, then to use this information to develop models to predict capability based on these governing principles. The hypothesis underscoring this work was that maximum voluntary hand force capability is governed by whole body balance, shoe-floor friction and joint strength; and consequently, psychophysically acceptable forces would be chosen proportionally to this maximum voluntary force capability, where the magnitude of the proportionality was dependent on the limiting factor, or ‘weakest link’. To investigate this hypothesis, both experimental and mathematical modeling paradigms were used. Initially, an experimental study was used to investigate how biomechanical factors governed maximum hand force capability across a range of exertions. It revealed that each governing factor differentially limited maximum force capability. Moreover, this study identified how foot placement, handle height, distance from the handle, friction, and body posture all influence the underlying biomechanical weakest link, and ultimately force producing capability. Data gathered in the experimental study was next used to evaluate a mathematical model that was developed to predict maximum force capability, given information on posture and direction of force application. In addition, the model also predicted population variability in maximum capacity based on the inclusion of a novel approach to probabilistically represent population variability. The evaluation demonstrated that the model underestimated maximum hand force capability compared to measured hand forces by approximately 18, 26, and 41% during medial, pulling and downward exertions respectively. However, it appeared that the ‘weakest link’ principle for predicting maximum force capacity was plausible, as evidenced by significant rank ordered correlations between the measured and predicted hand forces. Further research investigated if psychophysically acceptable forces were selected as a proportion of task specific maximum voluntary force capability, where the proportionality was related to the biomechanical weakest link. Using an experimental design, psychophysically acceptable forces and corresponding maximum forces were measured. Participants chose psychophysically acceptable forces that were 4/5ths of their task specific maximum voluntary force capability when capability was limited by balance. Additionally, they choose psychophysically acceptable forces that were 2/3rds of their maximum voluntary force capability when capability was limited by joint strength. The identification and confirmation of a weakest link proportionality principle represents an important contribution to the field of occupational biomechanics. The weakest link proportionality principle was integrated into the model to allow prediction of: maximum voluntary hand force capability, the limiting factor, and psychophysically acceptable hand force capability. The updated model underestimated empirically measured psychophysically acceptable forces by 24% and 43% during downward and pulling exertions respectively. However, the original model underestimated the maximum hand force capacity by 23% and 34% during the same exertions, without the proportional relationships. This underestimation may be a result of the underlying assumption that joint strength is independent, resulting in an underestimation of maximum joint strength capacity and a corresponding underestimation of maximum hand force capacity. The underestimation may also be due to differences in strength capacities between the participants tested during this thesis compared to those tested in past research used to determine the maximum strength indices reported in the literature. This body of work supported the hypothesis that psychophysically acceptable forces are selected as a proportion of the maximum voluntary hand force, where the proportionality depends on the underlying biomechanical weakest link. The model is a promising first step towards predicting maximum and psychophysically acceptable occupational force threshold limits.

A series of experiments is described which uses a perceptual matching approach to study the effect of exogenous visual cues on perception of static and dynamic stimuli. Analogous experiments were carried out for orientation judgments of rotated Gabor patches and for direction of motion of coherent dot motion. Response time effects of cuing were found in all conditions. Cuing was found to improve accuracy of orientation judgments, while the effects on motion judgments were less reliable. Cuing was found to have substantially larger effects on quality of orientation judgments at low contrast levels. Other analyses performed found sequential trial effects and qualitatively different effects of canonical directions on orientation and motion judgments.

Thesis (Ph. D.)--University of California, San Diego, 2001. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of California, San Diego, and San Diego State University, 2004. / Vita. Includes bibliographical references.