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Biomedical subjects

J F Norman

Publications and source records attributed to J F Norman.

At least 19 recordsLinked to original sources
PubMed2001

Maternal atherogenic diet in swine is protective against early atherosclerosis development in offspring consuming an atherogenic diet post-natally.

Atherosclerosis found early in life suggests that it may arise from fetal adaptations during development in utero. We evaluated the effect of a maternal atherogenic diet on atherosclerosis development in offspring. Aortic fat deposition was evaluated by Sudan IV staining and coronary atherosclerosis was assessed histologically. Sows were fed an atherogenic diet (ath) or standard diet (std) throughout gestation. Twelve neonates (six per maternal diet group) were evaluated with no significant differences noted (P>0.05) in serum lipids or aortic fat deposition and there was no evidence of coronary atherosclerosis. Twenty offspring (10 per maternal diet group) were followed for 5 months forming the pubertal age group. Half of these swine received an atherogenic (ATH) diet (std-ATH and ath-ATH) and half received a standard (STD) diet (std-STD and ath-STD). Pubertal age swine on the ATH diet had significantly greater (P<0.05) serum lipids and aortic fat deposition compared with those on the STD diet, with significantly greater fat deposition (P<0.05) occurring in the std-ATH versus ath-ATH group. Coronary atherosclerosis was exhibited only in the std-ATH diet group. Our findings suggest that gestational diet may alter the body's management of cholesterol later in life, possibly providing a protective effect from atherosclerosis.

Animals↗
PubMed2001

Information concentration along the boundary contours of naturally shaped solid objects.

In this study of the informativeness of boundary contours for the perception of natural object shape, observers viewed shadows/silhouettes cast by natural solid objects and were required to adjust the positions of a set of 10 points so that the resulting dotted shape resembled the shape of the original silhouette as closely as possible. For each object, the observers were then asked to indicate the corresponding positions of the 10 points on the original boundary contour. The results showed that there was a close correspondence between the chosen positions of the points and the locations along the boundary contour that were local curvature maxima (convexities or concavities). This finding differs from that of Kennedy and Domander (1985 Perception 14 367-370), and shows that, at least for natural objects, the original hypothesis of Attneave (1954 Psychological Review 61 183-193) is valid--local curvature maxima are indeed important for the perception of shape.

Algorithms↗
PubMed2000

The perception and recognition of natural object shape from deforming and static shadows.

In this study of the informativeness of shadows for the perception of object shape, observers viewed shadows cast by a set of natural solid objects and were required to discriminate between them. In some conditions the objects underwent rotation in depth while in other conditions they remained stationary, thus producing both deforming and static shadows. The orientation of the light source casting the shadows was also varied, leading to further alterations in the shape of the shadows. When deformations in the shadow boundary were present, the observers were able to reliably recognize and discriminate between the objects, invariant over the shadow distortions produced by movements of the light source. The recognition performance for the static shadows depended critically upon the content of the specific views that were shown. These results support the idea that there are invariant features of shadow boundaries that permit the recognition of shape (cf Koenderink, 1984 Perception 13 321-330).

Discrimination, Psychological↗
PubMed2000

The temporal course of suppression during binocular rivalry.

Orthogonally oriented sinusoidal luminance gratings were dichoptically presented to the observers' left and right eyes. During the subsequent binocular rivalry, a small target was briefly presented (4AFC) to probe the strength of interocular suppression at various temporal latencies. Both stationary and moving rivalrous patterns were investigated. The purpose of experiment 1 was to compare the temporal characteristics of stationary and motion rivalry (0 and 1.2 deg s-1), while that of experiment 2 was to examine rivalry suppression for higher speeds (2 and 4 deg s-1). In all cases, it was found that the strength of suppression remained essentially constant throughout a single phase of binocular rivalry. The results of the investigation also revealed that moving rivalrous patterns lead to greater magnitudes of interocular suppression than static patterns. Despite these differences in the strength of suppression, the results of both experiments show that the temporal characteristics of motion and static rivalry are essentially identical.

Female↗
PubMed2000

The effects of age upon the perception of depth and 3-D shape from differential motion and binocular disparity.

The ability of younger and older adults to perceive the 3-D shape, depth, and curvature of smooth surfaces defined by differential motion and binocular disparity was evaluated in six experiments. The number of points defining the surfaces and their spatial and temporal correspondences were manipulated. For stereoscopic sinusoidal surfaces, the spatial frequency of the corrugations was also varied. For surfaces defined by motion, the lifetimes of the individual points in the patterns were varied, and comparisons were made between the perception of surfaces defined by points and that of more ecologically valid textured surfaces. In all experiments, the older observers were less sensitive to the depths and curvatures of the surfaces, although the deficits were much larger for motion-defined surfaces. The results demonstrate that older adults can extract depth and shape from optical patterns containing only differential motion or binocular disparity, but these abilities are often manifested at reduced levels of performance.

Adult↗
PubMed2000

The perception of length on curved and flat surfaces.

In three experiments, observers judged the apparent extents of spatial intervals along the surface of a curved cylinder or a flat plane that was binocularly viewed in a natural, indoor environment. The observers' judgments of surface lengths were precise and reliable but were also inaccurate and subject to relatively large constant errors. These distortions differed among the observers, but they tended to perceive lengths oriented along the curved dimension of the cylinder as being longer than physically equivalent lengths in the noncurved dimension. This phenomenon did not occur when the observers judged curved and noncurved paths on the flat surface. In addition, some observers' judgments of length were affected by changes in the distance to the cylinder, whereas others were affected by the cylinder's orientation in space. These results demonstrate that the perception of length on surfaces is highly dependent on the particular context in which the length occurs.

Humans↗
PubMed2000

Exercise training effect on obstructive sleep apnea syndrome.

The role, if any, of exercise training in the management of individuals with obstructive sleep apnea syndrome (OSAS) is unclear. Anecdotally, patients have reported improvement in symptoms with regular participation in an exercise regime. In this study, we evaluated the effects of an exercise training program and weight loss on physical and subjective measures associated with OSAS. Nine subjects with mild to moderate OSAS completed a six month supervised exercise program. Pre and post-training measures on polysomnographic testing, physical training, anthropometric measures, quality of life (QOL), daytime somnolence and mood states were assessed. A significant decrease in the AHI (p=0.002) was noted along with improvements (p<0.05) in total sleep time, sleep efficiency, number of awakenings/hour, arousals/hour, apnea index and mean exercise training workloads. Significant decreases (p<.001) in weight (-6.2 kg) and body mass index (-1.6) were observed. Evaluation of QOL measures by the Health Status Questionnaire, Profile of Mood States and Epworth Sleepiness Scale showed significant changes in health status, affective state, and a decrease in daytime somnolence. Regular exercise training had a positive impact on the AHI, aerobic capacity, body mass index and QOL. However, exercise training alone was not an adequate intervention strategy for most individuals with OSAS but may serve well as an adjunct treatment strategy in the conservative management of individuals with mild to moderate OSAS.

Adult↗
PubMed1998

The perception of scale-dependent and scale-independent surface structure from binocular disparity, texture, and shading.

The integration of binocular disparity, shading, and texture was measured for two different aspects of three-dimensional structure: (1) shape index, which is a measure of scale-independent structure, and (2) curvedness, which is a measure of scale-dependent structure. Binocular disparity was found to contribute significantly more to judged shape index than it does to judged curvedness, and shading and texture were both found to contribute more to judged curvedness than to judged shape index. These results demonstrate that different cues do not contribute equally to different aspects of perceived surface structure. This finding suggests that, for the case of linear integration, multiple cues to three-dimensional structure do not combine on the basis of a single type of representation shared by all the 'shape-from-X' processes in the visual system.

Contrast Sensitivity↗
PubMed1998

Stereoscopic discrimination of interval and ordinal depth relations on smooth surfaces and in empty space.

In a series of three experiments, observers judged the perceived relative depths of small probe dots, which could be presented in empty space or attached to a smoothly curved surface. Discriminations of ordinal depth were found to be more precise than discriminations of depth intervals. The amount of separation in the projected image between the locations in depth was also manipulated. Performance was higher when observers evaluated the depth relationships between nearby points in the projected images, and lower when the points were more widely separated. This effect was most pronounced when there was a continuous surface in between the points, suggesting that accurate knowledge of the three-dimensional structure of surfaces is primarily limited to relatively small local neighborhoods.

Depth Perception↗
PubMed1998

On the relative salience of Euclidean, affine, and topological structure for 3-D form discrimination.

A match-to-sample task was performed, in which observers compared configurations of line segments presented stereoscopically in different three-dimensional orientations. Several different structural properties of these configurations were manipulated, including the relative orientations of line segments (a Euclidean property), their coplanarity (an affine property), and their patterns of cointersection (a topological property). Although the differences in these properties to be detected were all metrically equivalent, they varied dramatically in their relative perceptual salience, such that the error rates and reaction times in the three conditions varied by as much as 400%. Performance was highest in the topological condition, intermediate in the affine condition, and lowest in the Euclidean condition. These findings suggest that the relative perceptual salience of object properties may be systematically related to their structural stability under change, in a manner that is similar to the Klein hierarchy of geometries.

Depth Perception↗
PubMed1997

Integration of binocular stereopsis and structure from motion in the discrimination of noisy surfaces.

Integration of stereo and motion information was measured on the basis of observers' ability to discriminate between triangle- and sine-wave corrugated surfaces or sinusoidal surfaces of different spatial frequency. Discrimination performance for the triangle-sine task was consistent with independent processing of motion and stereo, but the spatial frequency discrimination task led to performance superior to that predicted by an independent combination of motion and stereo signals, indicating that the integration of stereo and motion depends on the type of 3-dimensional structure observers are required to discriminate. This pattern of results is consistent with the existence of multiple stereoscopic mechanisms suggested by psychophysical and neurophysiological data.

Depth Perception↗
PubMed1997

Effects of texture, illumination, and surface reflectance on stereoscopic shape perception.

Observers viewed computer-generated stereograms of randomly structured smooth surfaces and were required to judge the perceived local orientation at numerous probe points by adjusting a monocular gauge figure. The surfaces were depicted with specular or Lambertian reflectance functions, either with or without identifiable texture elements, and with varying directions of illumination. The results revealed a strong linear correlation between the judged patterns of relief and the actual depicted objects, though there were systematic differences in the magnitude of depth scaling in the different conditions. In general, the accuracy and reliability of observers' judgments for the smoothly shaded shiny surfaces was slightly lower than for the textured surfaces and slightly higher than for the smoothly shaded Lambertian surfaces. The direction of illumination had no detectable effect on the observers' judgments.

Computer Graphics↗
PubMed1996

The visual perception of three-dimensional length.

A set of 4 experiments evaluated observers' sensitivity to three-dimensional (3-D) length, using both discrimination and adjustment paradigms with computer-generated optical patterns and real objects viewed directly in a natural environment. Although observers were highly sensitive to small differences in two-dimensional length for line segments presented in the frontoparallel plane, their discrimination thresholds increased by an order of magnitude when the line segments were presented at random orientations in 3-D space. There were also large failures of constancy, such that the perception of 3-D length varied systematically with viewing distance, even under full-cue conditions.

Computer-Aided Design↗
PubMed1996

Surface range and attitude probing in stereoscopically presented dynamic scenes.

The authors report on different methods to probe the structure of visually perceived surfaces in 3 dimensions. The surfaces are specified by patterns of shading with Lambertian and specular components, which deform over time and over stereoscopic views. Five observers performed 2 probe tasks, 1 involving the adjustment of a punctate probe so as to be on the apparent surface and the other involving the adjustment of a small gauge figure that indicates surface attitude. The authors found that these rather different methods yielded essentially identical depth maps up to a linear transformations and that the observers all deviate slightly from veridicality in basically identical ways. The nature of this deviation appears to be correlated with the rough topography of the specularities.

Attention↗
PubMed1996

The discriminability of local surface structure.

The ability of observers to discriminate depth and orientation differences between separated local regions on object surfaces was examined. The objects were defined by many optical sources of information simultaneously, including shading, texture, motion, and binocular disparity. Despite the full-cue nature of the displays, the observers' performance was relatively poor, with Weber fractions ranging from 10% to 40%. The Weber fractions were considerably lower for discriminations of surface-orientation differences than for similar discriminations of depth differences. The ability of observers to discriminate surface-orientation differences was approximately invariant over the separation of the regions in the projected image. In contrast, the ability to discriminate depth differences was highly influenced by the amount of image separation. This qualitative difference between the perception of depth intervals and surface-orientation differences suggests that knowledge of depths and orientations may be represented separately within the human visual system.

Depth Perception↗
PubMed1996

Spatial interactions in perceived speed.

Previous research has shown that the perception of motion within a local region is influenced by other motions within neighboring areas (eg induced motion). Here, a study is reported of the perceived speed of dots moving within a circular target region, which was surrounded by other motions within a larger surrounding area. The perceived speed of the central dots was found to be fastest when the surround was stationary; it became slower as the speed of motion in the surround was increased. This decrease in the perceived target speed with increases in surround velocity occurred regardless of whether the direction in which the surround moved was the same as or opposite to the motion of the target region. This result cannot be explained by using simple models of perceived speed that depend only upon such factors as the magnitude of relative motion between center and surround. The spatial area over which these motion interactions occur was also investigated.

Analysis of Variance↗
PubMed1996

The visual perception of rigid motion from constant flow fields.

Four experiments investigated observers' judgments of rigidity for different types of optical motion. The depicted structural deformations were of two types: (1) those with nonparallel image trajectories that are detectable from the first-order spatiotemporal relations between pairs of views; and (2) those with parallel image trajectories that can only be detected from higher order relations among three or more views. Patterns were composed of smooth flow fields in Experiments 1 and 3, and of wire frame figures in Experiments 2 and 4. For both types of display, the nonrigidity detectable from the first-order spatiotemporal structure of the motion sequence was much more salient than the deformation detectable only from the higher order spatiotemporal structure. These results indicate that observers' judgments of rigidity are based primarily on a two-view analysis, but that some useful information can be obtained under appropriate circumstances from higher order spatiotemporal relations among three or more views.

Adult↗