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At least 1,351 records · Page 75Linked to original sources
PubMed1999

Anisotropy in the extended haptic perception of longitudinal distances.

Using horizontal rotational motions of a hand-held rod, participants in four experiments probed the aperture between two blocks separated in depth. The farther block could be either on the outer or on the inner side of the hand-rod system, defining apertures of opposite sense. The participants reported the perceived size of the in-depth intervals by adjusting, with the nonprobing hand, the lateral separation between two blocks or the egocentric distances of two blocks. Over variations in hand and geometric arrangement of stimulus and report blocks, perceived aperture size depended on the aperture's sense: Apertures with the farther edge on the outer side of the hand-rod were reported as being larger than their mirror image counterparts. The effect was not observed in judgments of a single edge distance (Experiment 5); it was configuration dependent. The sense effect would not be expected from the physical quantity accommodating perceived frontal apertures. Possible expansions of the physical model are discussed.

Adult↗
PubMed1999

Learning to see 3-D: psychophysics and brain electrical activity.

We investigated human perceptual learning with stereoscopic stimuli presented below threshold. Different visual patterns were shown as dynamic random dot stereograms in a forced-choice design in order to determine the psychophysical thresholds of 16 adults. Brain electrical activity was recorded from 30 electrodes over parieto-occipital areas while stereograms were presented with horizontal disparities below threshold. During the observation of sub-threshold stimuli, we tested repeatedly whether implicit perceptual learning occurred. More than half of the subjects learned to see stereoscopic targets. This was accompanied by topographic changes in the pattern of activation of neural assemblies in the visual cortex where the center of activity shifted towards the right hemisphere. Subjects who did not improve in perception, displayed no such effects.

Adult↗
PubMed1991

Perception of visual illusions in a sample of Nigerian children.

This study examined the effects of cultural factors on perception of 15 boys and 21 girls in Nigeria. The five geometric illusions of Segall, Campbell, and Herskovitz were shown in booklets. Previously tested Afghan boys gave evidence of greater illusion than the Nigerian children. The findings also supported previous research on perception of illusion.

Attention↗
PubMed1983

Infants' cross-modal transfer from solid objects to their graphic representations.

12-month-old infants were familiarized either tactually or visually with objects and then tested for visual recognition memory using either (1) the familiar and a novel object, (2) colored pictures of the objects, or (3) outline drawings of them. In Study 1, infants showed recognition memory on all 3 visual intramodal problems but showed cross-modal transfer only when objects were used as test stimuli. With increased familiarization times in Study 2, transfer from tactually presented samples to both pictorial displays was achieved, indicating that after feeling an object the infants were able to recognize it visually solely on the basis of its contour. With reduced familiarization times in Study 3, there was no evidence for transfer from visually presented samples to the 2 pictorial displays, replicating the pattern of results observed cross-modally in Study 1 and suggesting that, at least in certain respects, cross-modal and intramodal perception follow similar principles.

Depth Perception↗
PubMed1985

Object perception and object-directed reaching in infancy.

Five-month-old infants were presented with a small object, a larger object, and a background surface arranged in depth so that all were within reaching distance. Patterns of reaching for this display were observed, while spatial and kinetic properties of the display were varied. When the infants reached for the display, they did not reach primarily for the surfaces that were nearer, smaller, or presented in motion. The infants reached, instead, for groups of surfaces that formed a unit that was spatially connected and/or that moved as a whole relative to its surroundings. Infants reached for the nearer of two objects as a distinct unit when the objects were separated in depth or when one object moved relative to the other. They reached for the two objects as a single unit when the objects were adjacent or when they moved together. The reaching patterns provided evidence that the infants organized each display into the kind of units that adults call objects: manipulable units with internal coherence and external boundaries. Infants, like adults, perceived objects by detecting both the spatial arrangements and the relative movements of surfaces in the three-dimensional layout.

Depth Perception↗
PubMed2004

Bistability and biasing effects in the perception of ambiguous point-light walkers.

The perceptually bistable character of point-light walkers has been examined in three experiments. A point-light figure without explicit depth cues constitutes a perfectly ambiguous stimulus: from all viewpoints, multiple interpretations are possible concerning the depth orientation of the figure. In the first experiment, it is shown that non-lateral views of the walker are indeed interpreted in two orientations, either as facing towards the viewer or as facing away from the viewer, but that the interpretation in which the walker is oriented towards the viewer is reported more frequently. In the second experiment the point-light figure was walking backwards, making the global orientation of the point-light figure opposite to the direction of global motion. The interpretation in which the walker was facing the viewer was again reported more frequently. The robustness of these findings was examined in the final experiment, in which the effects of disambiguating the stimulus by introducing a local depth cue (occlusion) or a more global depth cue (applying perspective projection) were explored.

Adult↗
PubMed1996

Preattentive perception of elementary three-dimensional shapes.

Experiments in which a single target pattern is discriminated from multiple background distractors show that certain shaded, two-dimensional (2-D) stimuli consistent with a top-lit, polyhedral interpretation can be processed fast (< 80 msec) and in parallel. Unshaded line drawings of the same shapes, however, are processed serially. Strong pop-out asymmetries and control experiments involving shaded patterns that do not have familiar 3-D interpretations suggest that such fast, parallel processing is dependent upon perception 3-D shape. Furthermore, this process can be influenced by contextual scene information, in a manner that is dependent upon whether the additional cues contribute to the perception of a consistent 3-D scene.

Adolescent↗
PubMed1979

Illusory contours as the solution to a problem.

The perception of certain figures with illusory contours entails a reversal of figure and ground. It is hypothesized that this process occurs in two stages. First, some factor must suggest or cue the reversal. Experiments are described that isolate three such factors, namely, alignment of physically present contours, recognized incompletion of parts of the stimulus array, and set. Once cued, however, other experiments indicate that in a further stage of processing the solution is examined with respect to its compatibility with the stimulus display or with other preceptual properties to which the display gives rise. Only if such compatibility is present will the perception of a figure with illusory contours be maintained.

Cues↗
PubMed1991

The perception of mirror-reflected objects.

In what ways and under what conditions does an object appear to differ from its enantiomorph (its mirror reflection)? This 'mirror question' or its popular counterpart, "Why does a mirror reverse left and right but not up and down?" is frequently encountered, but an acceptable answer is not to be found in the literature. The question is approached as an experimental problem in visual psychophysics. A mirror optically reverses the axis perpendicular to its surface. What are the perceptual consequences of this stimulus transformation? This question is examined in four experiments by using stimuli of varying complexity and familiarity. Apparent reversals are demonstrated along right-left, front-back, top-bottom, and oblique axes, depending on the perceived asymmetries of the stimulus object. Perceived asymmetry is shown to depend both on structural asymmetries and on canonical axes and orientations defined by social convention. It is concluded that an object appears to differ from its enantiomorph by an apparent reversal along the axis of least perceived asymmetry. Implications for perceptual frames of reference and for the perception of symmetry are discussed.

Adult↗
PubMed2003

The effect of texture relief on perception of slant from texture.

Texture can be an effective source of information for perception of slant and curvature. A computational assumption required for some texture cues is that texture must be flat along a surface. There are many textures which violate this assumption, and have some sort of texture relief: variations perpendicular to the surface. Some examples include grass, which has vertical elements, or scattered rocks, which are volumetric elements with 3-D shapes. Previous studies of perception of slant from texture have not addressed the case of textures with relief. The experiments reported here test judgments of slant for textures with various types of relief, including textures composed of bumps, columns, and oriented elements. The presence of texture relief was found to affect judgments, indicating that perception of slant from texture is not robust to violations of the flat-texture assumption. For bumps and oriented elements, slant was underestimated relative to matching flat textures, while for columns textures, which had visible flat top faces, perceived slant was equal or greater than for flat textures. The differences can be explained by the way different types of texture relief affect the amount of optical compression in the projected image, which would be consistent with results from previous experiments using cue conflicts in flat textures. These results provide further evidence that compression contributes to perception of slant from texture.

Analysis of Variance↗
PubMed1996

Stereopsis with normal and reversed binocular parallax using a head mounted display in normal and strabismic subjects.

A virtual reality system using a head mounted display (HMD) was constructed for the purpose of finding out how human beings perceive the three-dimensional world. Four ophthalmologically normal subjects and 4 strabismic patients (2 with exotropia, 2 with esotropia) were examined. They wore the HMD and viewed some familiar objects (e.g. human face) and an unfamiliar object (e.g. tangled ropes) under normal parallax, reversed parallax, and monocular conditions. They also attempted the ring and hook test under each condition. They recognized the normal familiar objects under each condition, but some normal subjects were confused when they perceived unfamiliar objects. The normal subjects barely passed the ring and book test under the reversed parallax condition. The results of the strabismic subjects showed change under each condition. Stereoptic ability in normal and strabismic patients were considered based on the above. Also considered were some stereoptic keys, binocular parallax, monocular stereoptic keys such as shadows, shades, texture, etc., the near reflex and the fact that the objects were familiar. It was found that the strabismic patients used monocular stereoptic keys more than normal people to supplement their lack of binocular parallax perception.

Adult↗
PubMed2005

Is prior knowledge of object geometry used in visually guided reaching?

We investigated whether humans use prior knowledge of the geometry of faces in visually guided reaching. When viewing the inside of a mask of a face, the mask is often perceived as being a normal (convex) face, instead of the veridical, hollow (concave) shape. In this "hollow-face illusion," prior knowledge of the shape of faces dominates perception, even when in conflict with information from binocular disparity. Computer images of normal and hollow faces were presented, such that depth information from binocular disparity was consistent or in conflict with prior knowledge of the geometry. Participants reached to touch either the nose or cheek of the faces or gave verbal estimates of the corresponding distances. We found that reaching to touch was dominated by prior knowledge of face geometry. However, hollow faces were estimated to be flatter than normal faces. This suggests that the visual system combines binocular disparity and prior assumptions, rather than completely discounting one or the other. When comparing the magnitude of the hollow-face illusion in reaching and verbal tasks, we found that the flattening effect of the illusion was similar for verbal and reaching tasks.

Cognition↗
PubMed1986

Note on nonveridical visual perception and pedestrian accidents at night.

It is sometimes supposed that increase of pedestrian conspicuity could lead to substantial reductions in pedestrian accidents at night. Available evidence is, however, not particularly encouraging. It is suggested that other factors affecting drivers' and pedestrians' perception may be involved.

Acceleration↗
PubMed2002

The perception and discrimination of local 3-D surface structure from deforming and disparate boundary contours.

In a series of four experiments, we evaluated observers' abilities to perceive and discriminate ordinal depth relationships between separated local surface regions for objects depicted by static, deforming, and disparate boundary contours or silhouettes. Comparisons were also made between judgments made for silhouettes and for objects defined by surface texture, which permits judgment based on conventional static texture gradients, conventional stereopsis, and conventional structure-from-motion. In all the experiments, the observers were able to detect, with relatively high precision, ordinal depth relationships, an aspect of local three-dimensional (3-D) structure, from boundary contours or silhouettes. The results of the experiments clearly demonstrate that the static, disparate, and deforming boundary contours of solid objects are perceptually important optical sources of information about 3-D shape. Other factors that were found to affect performance were the amount of separation between the local surface regions, the proximity or closeness of the regions to the boundary contour itself, and for the conditions with deforming contours, the overall magnitude of the boundary deformation.

Depth Perception↗