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801.
Synthese - We extend stit logic by adding a spatial dimension. This enables us to distinguish between powers and opportunities of agents. Powers are agent-specific and do not depend on an... 相似文献
802.
803.
Sex Roles - Information was obtained from 184 females and 157 males enrolled in grade 11 in six urban high schools. The majority of the students were of European descent (70%), but there were... 相似文献
804.
Astrid M. L. Kappers Jan J. Koenderink Inge Lichtenegger 《Attention, perception & psychophysics》1994,56(1):53-61
In two experiments, the active haptic identification of three-dimensional mathematically welldefined objects is investigated. The objects, quadric surfaces, are defined in terms of the shape index, a quantity describing the shape, and curvedness, a quantity describing overall curvature. Both shape index and curvedness are found to have a significant influence on haptic shape identification . Concave surfaces lead to a larger spread in responses than convex ones. Hyperbolic surfaces show a slight tendency to be identified with more difficulty than elliptic ones. Surfaces with a high curvedness are identified more easily than those with a low curvedness. Results from experiments with constant and with random curvedness are indistinguishable . It is concluded that shape index and curvedness are psychophysically not confounded. 相似文献
805.
Jan J. Koenderink Andrea J. Van Doorn Astrid M. L. Kappers James T. Todd 《Attention, perception & psychophysics》1997,59(6):828-838
We asked subjects to match points on the surface of a smooth three-dimensional (3-D) shape with points on the surface of another object that was geometrically identical to the first object but was placed in a different pose, was differently textured, and was differently shaded. In all cases, the fiducial point was on the rim of one of the objects (i.e., the boundary of the visible region of the surface), whereas the matching point was well within the silhouette of the other object. This allowed us to draw (preliminary) conclusions concerning the way monocular human observers are able to handle the neighborhood of the rim, where the local slant assumes arbitrarily high values. All experiments were done in real space with real objects (no computer-simulated scenes), the points being indicated with laser beam illumination. The subject was given control over the direction of the laser beams and was thus able to perform the task by adjustment from the vantage position. We studied both consistency (whether the subject’s judgments were invariant against changes of relative pose) and veridicality (whether the depth of the visual contour as calculated from the settings agreed with the true distance as measured by mechanical means). Subjects caught much of the 3-D structure of the contour but did deviate appreciably and apparently idiosyncratically from the true geometry. 相似文献
806.
Susan F. te Pas Astrid M. L. Kappers Jan J. Koenderink 《Attention, perception & psychophysics》1997,59(4):567-579
We investigated the extent to which the human visual system can detect discontinuities in firstorder optical flow fields. We constructed two types of spatial discontinuities: a circular split field with a straight edge and a disk with annular surround. We used two different first-order optical flow components: an expansion and a rotation. We found an intriguing difference in the detection thresholds for straight and circular discontinuities. Whereas straight discontinuities yielded thresholds of 10%— 50% difference in expansion or rotation, circular discontinuities could, at first, only be detected at extreme differences (>>100%). After a learning period, thresholds for such stimuli decreased, but they remained significantly higher than thresholds for the straight edge. Thresholds rose for stimuli that formed a gradual transition between a circular and a straight edge, and they decreased with increasing eccentricity of the circular discontinuity. Results suggest that symmetry in the stimulus, defined by the coincidence of the center of expansion or rotation and the center of the circular discontinuity, was responsible for the difference in thresholds for circular and straight discontinuities. 相似文献
807.
Jan Narveson 《Ratio》1997,10(3):280-295
808.
Konrad J. Burdach Jan H. A. Kroeze E. P. Köster 《Attention, perception & psychophysics》1984,36(3):205-208
Four odor substances (lemon aroma, rum aroma, ethyl butyrate, and amyl acetate) in different concentrations were presented nasally and orally (retronasally) in a four-alternative forced-choice procedure (detection tasks). In a further experimental condition, sucrose was added to the stimuli. Finally, the taste properties of the (nonsugared) odor stimuli were judged on seven semantic scales. In the detection of odor-containing stimuli, there were no significant differences between nasal and retronasal stimulation. In the taste conditions, however, there was a significant decline of “hits” when the stimuli contained sucrose in addition to the odor substances. Furthermore, in semantic scaling of the taste stimuli, a new variant of the taste-smell illusion was observed, namely, a tendency to attribute “suited” basic taste categories (e.g., “sweet”) to pure (nongustatory) odor stimuli. 相似文献
809.
Upper bounds for Kruskal's stress 总被引:1,自引:0,他引:1
In this paper the relationships between the two formulas for stress proposed by Kruskal in 1964 are studied. It is shown that stress formula one has a system of nontrivial upper bounds. It seems likely that minimization of this loss function will be liable to produce solutions for which this upper bound is small. These are regularly shaped configurations. Even though stress formula two yields less equivocal results, it seems to be expected that minimization of this loss function will tend to produce configurations in which the points are clumped. These results give no clue as to which of the two loss functions is to be preferred.This study has been supported by the Nederlandse Organisatie voor Zuiver-Wetenschappelijk Onderzoek (Netherlands Organization for the Advancement of Pure Research), under grant 56-146.Comments by Willem Heiser and Frank Critichley have been very helpful.The second author presently is employed by the Netherlands Central Bureau of Statistics, Voorburg. 相似文献
810.
The paper reports on a longitudinal study of young people with severe learning difficulties. Two types of comparison are made: changes between Time 1 and Time 2, and comparisons with the younger age group in the study. The young adults acquired considerably more self-help and communication skills between Time 1 and Time 2. They were less likely to require help with self care than the younger age group and their carers were less stressed. Parents' needs for additional service provision fell into three categories: information needs, help with communication and other skills, and practical help. The greatest need was for information. The main concerns of the mothers at Time 1 and Time 2 are documented. The young adults' preparation for leaving school, current day placements at Social Education Centres and employment prospects are discussed. It is concluded that there are few opportunities to move on to less sheltered environments. 相似文献