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At least 523 records · Page 29Linked to original sources
PubMed1986

Role of task factors in visual field asymmetries.

Any tachistoscopic study of cerebral hemisphere asymmetry imposes a variety of task demands on the participants, ranging from demands imposed by specific viewing conditions to demands imposed by response output requirements. The present article discusses the role of several task factors that influence processing after the initial reception of the stimulus input, suggests a theoretical rationale for some of the effects of these task factors, and considers implications for future studies of visual laterality. The task factors discussed include both those that are relevant for minimizing artifacts that have nothing to do with hemispheric asymmetry and those that are relevant for interpreting hemispheric asymmetry in terms of specific perceptual and cognitive processes.

Attention↗
PubMed2000

Comparing extra-retinal information about distance and direction.

The idea that extra-retinal information about the orientation of the eyes could be used to judge an object's distance has a long history, and has been the issue of considerable debate throughout this century. We here show that the poor performance in comparison with judgements of direction has geometrical rather than physiological reasons, and discuss why previous studies have misled us into believing that information about distance is even poorer than the geometry predicts.

Convergence, Ocular↗
PubMed1999

Human cortical regions involved in extracting depth from motion.

We used functional magnetic resonance imaging (fMRI) to investigate brain regions involved in extracting three-dimensional structure from motion. A factorial design included two-dimensional and three-dimensional structures undergoing rigid and nonrigid motions. As predicted from monkey data, the human homolog of MT/V5 was significantly more active when subjects viewed three-dimensional (as opposed to two-dimensional) displays, irrespective of their rigidity. Human MT/V5+ (hMT/V5+) is part of a network with right hemisphere dominance involved in extracting depth from motion, including a lateral occipital region, five sites along the intraparietal sulcus (IPS), and two ventral occipital regions. Control experiments confirmed that this pattern of activation is most strongly correlated with perceived three-dimensional structure, in as much as it arises from motion and cannot be attributed to numerous two-dimensional image properties or to saliency.

Adolescent↗
PubMed1988

"Ratio" and "difference" judgments for length, area, and volume: are there two classes of sensory continua?

Subjects were required to judge ratios and differences of (a) line length for pairs of lines, (b) area for pairs of squares, and (c) volume for pairs of cubes. Nonmetric analyses of these judgments indicated that all subjects were able to make consistent ratio judgments for all three continua. Many of the subjects, when asked to judge subjective differences, however, performed as if they were judging subjective ratios rather than differences. The data for the few subjects who appeared to be judging subjective differences were not consistent across subjects and conditions. Previous studies of ratio and difference judgments of loudness and heaviness, on the other hand, showed the opposite pattern, in that subjects most often behaved as if they were judging sensory differences when asked to judge sensory ratios. We propose that ratio judgments are more natural to perceptual continua along which stimuli are easily "decomposed" into a number of smaller perceptual units.

Attention↗
PubMed1989

Shape from shadows.

The colors, textures, and shapes of shadows are physically constrained in several ways in natural scenes. The visual system appears to ignore these constraints, however, and to accept many patterns as shadows even though they could not occur naturally. In the stimuli that we have studied, the only requirements for the perception of depth due to shadows were that shadow regions be darker than the surrounding, nonshadow regions and that there be consistent contrast polarity along the shadow border. Three-dimensional shape due to shadows was perceived when shadow areas were filled with colors or textures that could not occur in natural scenes, when shadow and nonshadow regions had textures that moved in different directions, or when they were presented on different depth planes. The results suggest that the interpretation of shadows begins with the identification of acceptable shadow borders by a cooperative process that requires consistent contrast polarity across a range of scales at each point along the border. Finally, we discuss how the identification of a shadow region can help the visual system to patch together areas that are separated by shadow boundaries, to identify directions of surface curvature, and to select a preferred three-dimensional interpretation while rejecting others.

Attention↗
PubMed1976

An investigation of the relationship between viewing condition and preference for true and modified linear perspective and adults.

In four experiments, pictures varying in degree of perspective convergence from linear to parallel were observed under the following conditions: at an arbitrary station point, at correct station points, and with unconstrained view. Adults were asked to rank the pictures from the most to least natural and realistic-looking picture or from the most to the least accurate drawing. Subjects nearly always chose the parallel perspective pictures as most preferred and the linear perspective pictures as least preferred. Intermediate degrees of convergence were ranked accordingly. Results were interpreted in light of an argument for a pictorial station poing independent of the correct center of projection for a picture. Since this station point was calculated to be at a distance at least 10 times as great as the object is large, its assumption for pictorial viewing was termed the "Zoom "effect.

Adult↗
PubMed1977

Differential visual persistence between the two eyes: a model for the Fertsch-Pulfrich effect.

By presenting moving bars of different widths to the two eyes, an attempt was made to model the differential visual persistence produced by differential intensity filtering in the two eyes (the Fertsch-Pulfrich effect). If the phase of the two moving bars was controlled so that the thinner bar lined up with the leading edge of the wider bar, a clear depth effect was seen, which was the same as that produced by placing a filter in front of the eye seeing the wider bar. The depth effect was reversed, for example, from clockwise to anticlockwise, when the trailing edges of the targets were in alignment. These effects were additive to those produced by differential intensity filtering. When observers were permitted to control the phase relation between the two target bars in order to null the depth effect, they placed the thinner bar in alignment with the geometrical center of the wider bar. Widening the variable bar led to a reduction in its luminance, but this did not in itself seem to entail a Fertsch-Pulfrich effect. The classical latency explanation of the differential filtering effect is questioned, and a model involving spatial averaging of visual direction in conditions of differential persistence is proposed in its stead. Possible differences in the mechanisms of static and dynamic stereopsis are discussed.

Depth Perception↗
PubMed1981

Alternative solutions to kinetic stimulus transformations.

It has been assumed that certain stimulus transformations lead directly to depth effects, that is, that such transformations are the necessary and sufficient conditions for kinetically generated depth perception. An alternative is to view such perception as the preferred solution to the problem posed by the transforming stimulus as to what even in the world is producing that transformation. In several experiments it is shown that when other solutions are supportable by the stimulus, those same transformations will no longer lead to depth perception. These other solutions become preferred on the basis of rejection of certain coincidental features of the stimulus that otherwise would have to be accepted were the kinetic depth solution to be maintained. The findings are interpreted as challenging any theory that perception is simply the direct result of stimulation or of extraction of stimulus information and as supporting the Helmkoltzian rule of perception as a construction of the most reasonable representation.

Depth Perception↗
PubMed1981

Antagonistic effects of adjacency and apparent speed in induced movement.

Two experiments concerning induced movement are reported. The hypothesis was that when outline inducing frames were used, object-relative displacement was modified by two variables, adjacency and apparent speed. Adjacency is directly related to the magnitude of induced movement. Small outline frames are high in adjacency, and so small frames should be powerful generators of induced movement. On the other hand, several investigators have found the speed of the inducing frame to be inversely related to the magnitude of induced movement. It is hypothesized here that this effect of speed was determined by apparent speed (not real speed), and if so, since small objects appeared to move faster than large ones, a small outline frame should be a relatively weak generator of induced movement. In the first experiment, this hypothesis was tested using single inducing frames. In the second experiment, this hypothesis was tested using two inducing frames presented simultaneously. The implications of these experiments were discussed with regard to other theories of induced movement.

Discrimination, Psychological↗
PubMed1989

Sensory-perceptual qualities of images.

Four experiments demonstrated that such sensory-perceptual features of objects as weight, color, and numerosity affect imaginal performance involving images of those objects. For example, imaginary transport times of objects increased with both the hypothetical weight of the imagined object and the distance traversed. The transport functions were steeper when a map of the terrain was imagined than when it was perceived, suggesting that imaginal performance of heft did not parallel more perceptually guided performance. Corresponding to the view that images activate noncanonical information from long-term memory, mental transport times were longer for maps of familiar terrains than for those of presumably unelaborated unfamiliar terrains. Further, the effects of imaginary color discriminations depended on the familiarity of the object being imagined. Images of customarily colored familiar objects were generated faster when projected onto a surface of the same color than when projected onto a surface of another color, whereas images constructed from unfamiliar targets were recognized more accurately when the target's color differed substantially from that of the ground than when it differed by a smaller amount. The results were predicted by a model that assumed that images may incorporate ancillary characteristics in addition to canonical information.

Adult↗