The underestimation of depth in virtual environments at mediumield distances is a well studied phenomenon. However, the degree by which underestimation occurs varies widely from one study to the next, with some studies reporting as much as 68% underestimation in distance and others with as little as 6% (Thompson et al. [38] and Jones et al. [14]). In particular, the study detailed in Jones et al. [14] found a surprisingly small underestimation effect in a virtual environment (VE) and no effect in an augmented environment (AE). These are highly unusual results when compared to the large body of existing work in virtual and augmented distance judgments [16, 31, 36–38, 40–43]. The series of experiments described in this document attempted to determine the cause of these unusual results. Specifically, Experiment I aimed to determine if the experimental design was a factor and also to determine if participants were improving their performance throughout the course of the experiment. Experiment II analyzed two possible sources of implicit feedback in the experimental procedures and identified visual information available in the lower periphery as a key source of feedback. Experiment III analyzed distance estimation when all peripheral visual information was eliminated. Experiment IV then illustrated that optical flow in a participant’s periphery is a key factor in facilitating improved depth judgments in both virtual and augmented environments. Experiment V attempted to further reduce cues in the periphery by removing a strongly contrasting white surveyor’s tape from the center of the hallway, and found that participants continued to significantly adapt even when given very sparse peripheral cues. The final experiment, Experiment VI, found that when participants’ views are restricted to the field-of-view of the screen area on the return walk, adaptation still occurs in both virtual and augmented environments.

Background: Due to the deficit of knowledge on fine motor skill far transfer from one domain of expertise to another, piano performance and surgical training serve as a relevant, interdisciplinary context in which to study the transfer of motor skills given both have relatively well-established levels of performance and require complex fine motor skills. Musicians tend to demonstrate greater ease in all aspects of procedural knowledge which are known to contribute to the early stages of motor learning. Previous research in the Piano Pedagogy Research Laboratory (PPRL) found that extensive piano training was correlated with faster learning of surgical knot-tying skills. However, the short-term two-day timeline was a limitation of the study. Objective: Our project has built on previous work in the PPRL to address the short-term nature of previous studies by measuring a long-term performance curve as well as retention of surgical training and also expanded on the previous project by focussing this time on laparoscopic tasks. This study compared performance curves of two participant groups (pianists and controls) over five consecutive days and retention one week later, as measured by speed and accuracy of task completion. Laparoscopic training consisted of six tasks repeated at every session. Since laparoscopy involves a variety of abilities concurrently, we also administered a battery of ten psychometric tests to isolate and measure specific aspects of non-motor and fine motor skills. Results: There was no statistical difference between participant groups on the majority of laparoscopic training and psychomotor assessments based on two-way mixed ANOVA and Mann-Whitney U test analysis, respectively. There were also little to no significant correlations between abilities and laparoscopic performance. The only significant confounding variable was that the control group was significantly more interested in surgery than the musician group (p = .037). Conclusion: Overall, these results demonstrate that piano performance training did not far transfer to laparoscopic surgery. This is relevant to the debate on far transfer of motor skills given this study’s robust design which addressed previous shortcomings by including a longer timeline and more specifications of musicians’ characteristics. Our findings indicate that fine motor skills are domain specific to music and surgery, respectively.

We explore the relative utility of shape from shading and binocular disparity for depth perception. Ray-traced images either featured a smooth surface illuminated from above (shading-only) or were defined by small dots (disparity-only). Observers judged which of a pair of smoothly curved convex objects had most depth. The shading cue was around half as reliable as the rich disparity information for depth discrimination. Shading- and disparity-defined cues where combined by placing dots in the stimulus image, superimposed upon the shaded surface, resulting in veridical shading and binocular disparity. Independently varying the depth delivered by each channel allowed creation of conflicting disparity-defined and shading-defined depth. We manipulated the reliability of the disparity information by adding disparity noise. As noise levels in the disparity channel were increased, perceived depths and variances shifted toward those of the now more reliable shading cue. Several different models of cue combination were applied to the data. Perceived depths and variances were well predicted by a classic maximum likelihood estimator (MLE) model of cue integration, for all but one observer. We discuss the extent to which MLE is the most parsimonious model to account for observer performance.

This exploration is one artist's view of visual reasoning through the study of depth perception. The experiment searched for pre-architectural forms through an investigation of geometric rectangular shapes and planar figures in anticipation of finding architectural volumes, that is, three-dimensional objects. I used three parameters to observe: the expected or planned, the anticipated, and the unforeseen. The pre-architectural sketching style used the disciplines of painting, sculpture, graphic arts, color theory, optics, and photography to formulate an architectural language. First, as artist (painter), I selected the medium of light as the brushstroke, color as the pigment, and photographic film plane as the canvas to capture image abstractions. Second, I used one-point perspective as the viewer's line of sight. Finally, I employed a series of shape abstractions to form a succession of transparent sections that composed the subject matter. This experiment sought to analyze visual perception by capturing the spatial depth of images, that is, a reproduction of something sculptural in likeness. The challenge was to reintegrate the abstracted Rectangular Shapes and Planar Figures. In order to achieve this physical abstraction, I created a modified camera obscura. This exploration produced clearly defined images-as-products that were interpreted as pre-architectural forms, which allowed me to translate color abstractions into architectural form studies, or models-as-products. Thus, the experiment created architectural volumes using light and color in order to draw points, lines, planes, and spatial depth. / Master of Architecture

To determine the test-retest reliability of the Randot stereoacuity test when used as part of vision screening in schools. METHODS: Randot stereoacuity (graded-circles) and logMAR visual acuity measures were gathered in an unselected sample of 139 children (aged 4-12, mean 8.1+/-2.1 years) in two schools. Randot testing was repeated on two occasions (average interval between successive tests 8 days, range: 1-21 days). Three Randot scores were obtained in 97.8% of children. RESULTS: Randot stereoacuity improved by an average of one plate (ie, one test level) on repeat testing but was little changed when tested on the third occasion. Within-subject variability was up to three test levels on repeat testing. When stereoacuity was categorised as 'fine', 'intermediate' or 'coarse', the greatest variability was found among younger children who exhibited 'intermediate' or 'coarse'/nil stereopsis on initial testing. Whereas 90.8% of children with 'fine' stereopsis (</=50 arc-seconds) on the first test exhibited 'fine' stereopsis on both subsequent tests, only approximately 16% of children with 'intermediate' (>50 but </=140 arc-seconds) or 'coarse'/nil (>/=200 arc-seconds) stereoacuity on initial testing exhibited stable test results on repeat testing. CONCLUSIONS: Children exhibiting abnormal stereoacuity on initial testing are very likely to exhibit a normal result when retested. The value of a single, abnormal Randot graded-circles stereoacuity measure from school screening is therefore questionable.

No / Postural instability in older people is associated with an increased risk of falling. This experiment investigated the effects of different gaze strategies on postural stability in older people, when using distance single-vision compared with multifocal (progressive addition lens and bifocal) spectacles. METHODS: Eighteen healthy older habitual multifocal spectacle-wearers (mean age 72.1 +/- 4.0 years) participated in a randomised, cross-over study. Postural stability during quiet standing was assessed as the root mean square excursion in the centre of pressure (RMS-COP) in the antero-posterior direction. Ground reaction force data were collected (for 30 seconds), while subjects viewed one of two visual targets (one square metre) of different spatial frequencies and contrasts, while wearing either distance single-vision or multifocal (progressive addition and bifocal) spectacles. The visual targets were positioned either ahead at eye-level or on the ground (viewing distance 2.06 metres) and viewed under the following head-gaze conditions; 'head neutral-gaze forward', 'head flexed-gaze down' and 'head neutral-gaze down'. RESULTS: The type of spectacles worn or the target viewed had no significant effect on postural stability but postural stability deteriorated (antero-posterior RMS-COP excursion increased) in the 'head neutral-gaze down' compared with the 'head flexed-gaze down' and 'head neutral-gaze forward' conditions (5.9, 5.5 and 5.0 mm respectively, p < 0.001). CONCLUSIONS: Multifocal use had no effect on standing postural stability. Irrespective of spectacles worn, when fixating a visual target positioned at ground level, postural stability was better in the 'head flexed-gaze down' condition compared with the 'head neutral-gaze down' condition. A useful strategy to reduce falling in the older person might be to advise multifocal and distance single-vision spectacle-wearers to flex their heads rather than just lower their eyes when looking downwards.

Recent applications in three-dimensional (3-D) presentation of information has emphasized the use of field-sequential stereoscopic CRT displays. The usefulness of stereopsis to present depth information has been studied in terms of performance measures such as search time, search accuracy, and subjective image quality ratings. Few, if any, studies have been conducted to investigate the influence of stereopsis upon cognitive workload. This dissertation is a description of two experiments using 3-D images presented on a Tektronix SGS 620 field-sequential stereoscopic CRT. Comparisons were made between presentations incorporating monocular cues only (2 1/2-D) and scenes containing monocular cues plus retinal disparity (3-D). In the first experiment, 11 participants were required to make inter-elements distance judgments under conditions of varying perspective angle, scene complexity, and depth cues while performing an interval production task. Accuracy was found to be significantly enhanced by the addition of retinal disparity as well as by decreases in the complexity of the presented scene. Cognitive workload increased significantly with increases in scene complexity, but no significant difference in workload was found between the stereoscopic and non-stereoscopic presentation formats. The second experiment investigated the effects of stereopsis on target identification under varying conditions of background complexity, target coding schemes, number of elements, signal-to-noise ratio, and depth cues. Accuracy measures, response time, and workload ratings were degraded by increases in scene background complexity, signal:noise ratio, and number of elements. Target coding methods which incorporated color were found to be significantly better than those in which targets were identified by shape only. No significant difference was found between 2 1/2-D and 3-D presentation for any of the dependent measures. The results indicate that retinal disparity it most appropriate for tasks, such as determination of object location in depth, in which the additional information provided by the depth cue is directly related to the task. Retinal disparity provides the most benefit for depth judgment tasks involving highly complex scenes. In cases of very simple tasks or simple scenes, the addition of retinal disparity is contra-indicated. / Ph. D.

La percepció per visió es millorada quan es pot gaudir d'un camp de visió ampli. Aquesta tesi es concentra en la percepció visual de la profunditat amb l'ajuda de càmeres omnidireccionals. La percepció 3D s'obté generalment en la visió per computadora utilitzant configuracions estèreo amb el desavantatge del cost computacional elevat a l'hora de buscar els elements visuals comuns entre les imatges. La solució que ofereix aquesta tesi és l'ús de la llum estructurada per resoldre el problema de relacionar les correspondències.S'ha realitzat un estudi sobre els sistemes de visió omnidireccional. S'han avaluat vàries configuracions estèreo i s'ha escollit la millor. Els paràmetres del model són difícils de mesurar directament i, en conseqüència, s'ha desenvolupat una sèrie de mètodes de calibració.Els resultats obtinguts són prometedors i demostren que el sensor pot ésser utilitzat en aplicacions per a la percepció de la profunditat com serien el modelatge de l'escena, la inspecció de canonades, navegació de robots, etc. / Vision perception is enhanced when a large field of view is available. This thesis is focused on the visual perception of depth by means of omnidirectional cameras. The 3D sensing is obtained in computer vision by means of stereo configurations with the drawback of feature matching between images. The solution offered in this dissertation uses structured light projection for solving the matching problem. First, a survey on omnidirectional vision systems was realized. Then, the sensor design was addressed and the particular stereo configuration of the proposed sensor was decided. An accurate model is obtained by a careful study of both components of the sensor. The model parameters are measured by a set of calibration methods.The results obtained are encouraging and prove that the sensor can be used in depth perception applications such as scene modeling, pipe inspections, robot navigation, etc.

D.Ed. / Stereopsis -- binocular depth perception is a visual function which falls within the ambit of the hyperacuities. The term, Hyperacuity, is one coined by Westheimer (1976) to describe thresholds of discrimination which cannot be explained on the basis of the optical components or sensory elements of the eyes alone. By implication such levels of discrimination are effected by higher levels of brain function. It is reasoned that an individual's stereoscopic hyperacuity should in some way relate to other measures of higher sensory and motor brain functions. In a school situation hyperacuity should relate to measures of intelligence, as well as scholastic and sporting achievement. The design and implementation of an experiment to test this premise forms the basis of this thesis. A literature review is reported of current knowledge relevant to this study together with a description of the stereoscopic testing instruments commonly available in clinical practice. A rationale for modifying these instruments and testing methods to suit the needs of this study is also included. This study exposes new knowledge about the process of static nearpoint stereopsis. This stereopsis proves to be a complex of diverse skills, which are significantly age-related and developmental in nature. These skills are seen to influence and be influenced by educational interventions. It may be concluded from this study that there is value in measuring stereopsis in more depth than has been done previously and that it is crucial to measure the speed of stereo performance in its own right in addition to the measures of stereoacuity. The study reveals significant differences of performance which relate to stereopsis in front as opposed to behind the plane of regard and also related to figure/ground contrast differences. The two non-stereoscopic tests and the six different stereoscopic tests described in this thesis prove to be highly discriminative and diagnostic with respect to age, grade level, I.Q., scholastic achievement and sporting ability.

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