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PubMed1979

Perception of simple figures: implicit-shape constancy and mental rotation.

Adults were shown simple figures either drawn on their own or on a face of a depicted cube. Under each of these conditions they were required to find identical figures in an array of stimuli of either the first or the second type. The response chosen determined the next stimulus used, the figures in both being identical. Four chains of 10 responses were thus obtained. Comparison of the choices reveals that the set consisting of 'plain' responses to 'cube' stimuli diverges significantly from the other three sets. This result is discussed in the context of other studies of implicit-shape constancy.

Adult↗
PubMedDate not supplied

Psychophysical and physiological evidence for viewer-centered object representations in the primate.

A key question concerning the perception of 3D objects is the spatial reference frame used by the brain to represent them. The celerity of the recognition process could be explained by the visual system's ability to quickly transform stored models of familiar 3D objects, or by its ability to specify the relationship among viewpoint-invariant features or volumetric primitives that can be used to accomplish a structural description of an image. Alternatively, viewpoint-invariant recognition could be realized by a system endowed with the ability to perform an interpolation between a set of stored 2D templates, created for each experienced viewpoint. In the present study we set out to examine the nature of object representation in the primate in combined psychophysical-electrophysiological experiments. Monkeys were trained to recognize novel objects from a given viewpoint and subsequently were tested for their ability to generalize recognition for views generated by mathematically rotating the objects around any arbitrary axis. The perception of 3D novel objects was found to be a function of the object's retinal projection at the time of the recognition encounter. Recognition became increasingly difficult for the monkeys as the stimulus was rotated away from its familiar attitude. The generalization field for novel wire-like and spheroidal objects extended to about +/- 40 degrees around an experienced viewpoint. When the animals were trained with as few as three views of the object, 120 degrees apart, they could often interpolate recognition for all views resulting from rotations around the same axis. Recordings from inferotemporal cortex during the psychophysical testing showed a number of neurons with remarkable selectivity for individual views of those objects that the monkey had learned to recognize. Plotting the response of neurons as a function of rotation angle revealed systematic view-tuning curves for rotations in depth. A small percentage of the view-selective cells responded strongly for a particular view and its mirror-symmetrical view. For some of the tested objects, different neurons were found to be tuned to different views of the same object; the peaks of the view-tuning curves were 40-50 degrees apart. Neurons were also found that responded to the sight of unfamiliar objects or distractors. Such cells, however, gave nonspecific responses to a variety of other patterns presented while the monkey performed a simple fixation task.

Animals↗
PubMed2005

Computational analyses for illusory transformations in the optic flow field and heading perception in the presence of moving objects.

When we see a stimulus of a radial flow field (the target flow) overlapped with a lateral flow field or another radial flow field, the focus of expansion (FOE) of the target radial flow appears to be shifted in a direction. Royden and Conti [(2003). A model using MT-like motion-opponent operators explains an illusory transformation in the optic flow field. Vision Research, 43, 2811-2826] argued that local motion subtraction is crucial for explanation of this phenomenon. The flow field which causes the illusory displacement of FOE was computationally analyzed. It was shown that the flow field is approximately a rigid-motion flow; the flow can be generated by simulating a situation where an observer moves toward a stationary scene. The heading direction for the observer corresponds to the perceived position of the FOE of the radial flow pattern. It implies that any algorithms which assume rigidity of the scene and recover veridical heading explain the bias in perceived FOE. There is no need for local motion subtraction in order to explain the phenomena. Furthermore, the flow for an observer's translation in the presence of objects moving laterally or in depth was computationally analyzed. It was found that algorithms which minimizes standard error functions with less weights to the independently moving objects show similar biases in recovered heading to the bias of human observers. It implies that local motion subtraction is not necessary for explanation of the bias in perceived heading due to an object moving laterally or in depth, contrary to the argument of Royden [(2002). Computing heading in the presence of moving objects: a model that uses motion-opponent operators. Vision Research, 42, 3043-3058].

Algorithms↗
PubMed1998

Modulation of cell responses to horizontal disparities by ocular vergence in the visual cortex of the awake Macaca mulatta monkey.

Horizontal retinal disparity is the most important cue for stereopsis. However, accurate stereoscopic perception requires additional information on fixation distance. The ocular vergence angle may provide information on fixation distance and therefore may be used to calibrate horizontal disparities. We studied the responses of cells from cortical visual area V1 of one macaca mulatta monkey to dynamic random dot stereograms at different ocular vergence angles. We observed that in about half of cells sensitive to horizontal disparity the vergence angle modifies the cell responses to horizontal disparities. These results suggest that vergence angle may be used to calibrate horizontal disparities for fixation distance.

Animals↗
PubMed2003

Changes in neural complexity during the perception of 3D images using random dot stereograms.

One developing theme in consciousness research is that consciousness is not the product of any specific component of the brain, rather it is an emergent property of the changing patterns of connectivity between different specialised functional components. For example, the dynamic core hypothesis proposes that conscious experience requires high levels of neural complexity, where complexity is defined in terms of functional connectivity. To test this hypothesis, electroencephalography was recorded while participants were shown random dot-stereograms. Consistent with the dynamic core hypothesis, neural complexity increased as the participants changed from simply viewing the stereogram to consciously perceiving the hidden 3D image.

Adult↗
PubMed2004

Perceiving virtual geographical slant: action influences perception.

In 4 experiments, the authors varied the extent and nature of participant movement in a virtual environment to examine the influence of action on estimates of geographical slant. Previous studies showed that people consciously overestimate hill slant but can still accurately guide an action toward the hill (D. R. Proffitt, M. Bhalla, R. Gossweiler, & J. Midgett, 1995). Related studies suggest that one's potential to act may influence perception of slant and that distinct representations may independently inform perceptual and motoric responses. The authors found that in all conditions, perceptual judgments were overestimated and motoric adjustments were more accurate. The virtual environment allowed manipulation of the effort required to walk up simulated hills. Walking with the effort appropriate to the visual slant led to increased perceptual overestimation of slant compared with active walking with the effort appropriate to level ground, while visually guided actions remained accurate.

Adolescent↗
PubMed2002

Cortical areas mediating stereopsis in the human brain: a PET study.

Using PET, we investigated the neural substrates of stereodepth perception in humans. The presentation of Julesz-type random-dot stereograms (RDS) produced significant rCBF elevations in Brodmann areas (BA) 18, 19 and 7, all in the right hemisphere. Activation foci were also found in both middle temporal areas (MT). These results demonstrate that, as in primates, cortical area MT and extrastriate areas are central to stereovision and that a network of predominant right hemispheric regions is recruited to meet visuo-spatial processing demands associated with horizontal binocular disparity inputs.

Adult↗
PubMed2005

Luminance edges are not necessary for visual completion.

Luminance edges seem to have an important role in visual feature binding and, more specifically, in visual completion because luminance differences are important for the perception of depth. We investigated this claim in two experiments in which the primed-matching paradigm was used. In Experiment 1, we investigated conditions under which either a partly occluded shape or an occluder was isoluminant with respect to the background. In Experiment 2, the partly occluded shape and the occluder were isoluminant with respect to each other. Evidence was found for visual completion in all cases, and we therefore conclude that luminance edges are not essential for visual completion.

Cues↗
PubMed2000

Touch can change visual slant perception.

The visual system uses several signals to deduce the three-dimensional structure of the environment, including binocular disparity, texture gradients, shading and motion parallax. Although each of these sources of information is independently insufficient to yield reliable three-dimensional structure from everyday scenes, the visual system combines them by weighting the available information; altering the weights would therefore change the perceived structure. We report that haptic feedback (active touch) increases the weight of a consistent surface-slant signal relative to inconsistent signals. Thus, appearance of a subsequently viewed surface is changed: the surface appears slanted in the direction specified by the haptically reinforced signal.

Biofeedback, Psychology↗
PubMed2002

Object pose: perceiving 3-d shape as sticks and slabs.

Estimating the pose (three-dimensional orientation) of objects is an important aspect of 3-D shape perception. We studied the ability of observers to match the pose of the principal axes of an object with the pose of a cross consisting of three perpendicular axes. For objects, we used a long and a flat spheroid and eight symmetric objects with aspect ratios of dimensions of approximately 4:2:1. Stimulus cues were the contour and stereo for the spheroids, and contour, stereo, and shading for the symmetric objects. In addition, the spheroids were shown with or without surface texture and with or without active motion. Results show that observers can perform the task with standard deviations of a few degrees, though biases could be as large as 30 degrees. The results can be naturally decomposed in viewer-centered coordinates, and it turns out that the estimation of orientation in the frontoparallel plane (tilt) is more precise than estimation of orientation in depth (slant, roll). A comparison of long and flat spheroids shows that sticks lead to better performance than do slabs. This can even be the case within the same object; the pose of the stick-like aspect is seen with more precision than is the pose of the slab-like aspect. The largest biases occurred when the spheroids were displayed with the binocular contour as the only cue. We can explain these biases by assuming that subjects' settings are influenced by the orientation of the rim.

Depth Perception↗
PubMedDate not supplied

[Stereoscopic perception. Probable intervention of pulvinar neurons in the cat (author's transl)].

With the aid of a programme of automatic analysis it has been possible to determine the visual fields of each eye in the case of binocular cells in the pulvinar, lateral-posterior and supageniculate nuclei. The visual properties determined by stimulation of one eye were often similar to those of the other eye. By an objective method of determination of the centre of activity of the receptive fields it was possible to measure disparities between large fields of neurons of these structures. These disparities are compatible with the intervention of these associative nuclei of the postero-lateral thalamus in the mechanisms in stereoscopic vision.

Animals↗
PubMed2005

The effects of field of view on the perception of 3D slant from texture.

Observers judged the apparent signs and magnitudes of surface slant from monocular textured images of convex or concave dihedral angles with varying fields of view between 5 degrees C and 60 degrees C. The results revealed that increasing the field of view or the regularity of the surface texture produced large increases in the magnitude of the perceptual gain (i.e., the judged slant divided by the ground truth). Additional regression analyses also revealed that observers slant judgments were highly correlated with the range of texture densities (or spatial frequencies) in each display, which accounted for 96% of the variance among the different possible dihedral angles and fields of view.

Depth Perception↗
PubMed2002

Apparent distance in actual, three-dimensional video-recorded, and virtual reality.

This study examined how well reality was reproduced in several conditions of virtual reality, by mutually comparing the perception of distance in actual 3-dimensional space and 3-dimensional video-recorded space. Apparent distances in both indoor and outdoor situations were estimated by 10 adolescents. Analysis showed that relations between apparent distance and physical distance in the actual spaces both in indoor and outdoor situations are described by 0.95 and 1.01 power exponents, respectively. On the other hand, the underestimations of the apparent distance are shown in the 3-dimensional video-recorded and the virtual reality spaces both in indoor and outdoor situations whose exponents ranged from .53 to .80.

Adult↗
PubMed1996

Perception of local orientation from shaded images.

The perception of local orientation from shaded images was examined. In Experiment 1, subjects viewed a boundaryless Gaussian hill and judged local orientation using both a gauge figure and a pointing method. One subject reported an internally consistent surface which was incompatible with the judged light-source direction and model used to generate the image. The remaining subjects reported a surface similar to the generating one, and analysis of their results indicated a contour of zero difference between response and generating slants. This contour of zero slant difference was explored in three subsequent experiments using the pointing technique. These experiments investigated possible influences of luminance artifact (Experiment 2), perception of global orientation (Experiment 3), and self-occluding contours (Experiment 4). All three of these experiments yielded results similar to those of Experiment 1, with distinct contours of zero slant difference. This contour was explored for relationships with the simulated slant of the generating surface and the differential structure of image intensity. This analysis indicated that the contour of zero slant difference was approximately a line of constant slant which shared large regions of adjacency to the zero crossings of the second directional derivative of image intensity.

Adult↗
PubMed2002

Seeing, since childhood, without ventral stream: a behavioural study.

We report the case of a 30-year-old man (S.B.) who developed visual agnosia following a meningoencephalitis at the age of 3 years. MRI disclosed extensive bilateral lesions of the occipital temporal visual pathway (ventral stream) and lesions in the right dorsal pathway, sparing primary visual cortices. S.B. showed a severe visual recognition deficit (texture, colour, objects, faces and words), although movement and space perception were largely preserved. His remaining visual capacities illustrate the competence of an isolated dorsal system which essentially functions on the sole basis of magnocellular afferents (low spatial resolution, high sensitivity to low contrast and moving stimuli). Patient S.B. also shows remarkable visuomotor competences, despite his perceptual limitations. It is suggested that his perceptual capacities correspond to the visual processing limitations of the dorsal visual stream, which in this patient have become accessible to perceptual awareness.

Adolescent↗
PubMed2002

A stochastic model of multistable visual perception.

Multistability in vision is an intriguing phenomenon that is currently not well understood. In this paper, we present a new, stochastic model for multistable visual perception. It is based on results of time series analysis of experimental data, yielding evidence for it being a linear, stochastic process. This is the outcome of testing for unstable periodic orbits and comparing the correlation dimension of the data to that of white noise. In the model, all degrees of freedom but one can be determined by general knowledge, thus resulting in a high degree of parsimony. The remaining parameter is used to model the individual characteristics that vary between subjects. Fitting simulations to the experimental data proves the parameter to be in a physiologically highly plausible range.

Depth Perception↗
PubMed1988

On a changing perspective illusion within Vermeer's The Music Lesson.

The effect of line of sight on the perception of spatial configuration has been investigated in a well-known painting (The Music Lesson by Vermeer) and in two control patterns. In experiment 1, subjects indicated the perceived inclination of two major contours which defined the sidewall-floor and backwall-floor joints in (i) a projected image of the painting, (ii) a three-line representation of the major spatial elements of the painting, and (iii) a three-dimensional wire model of these same contours, when standing in each of eighteen positions on a line running parallel to the surface of the screen. Results indicated a significant change in the perception of the sidewall-floor, but not of the backwall-floor contour, as viewing angle changed, in both the painting and the three-line representation. However, the angular setting in the latter case was significantly less than when the painting was used, ie subjects underestimated the depicted inclination. Settings for the wire model did not deviate with viewing angle and reflected geometrically correct adjustments. In experiment 2, the results of experiment 1 were confirmed using enantiomorphs. These findings are discussed in the light of other view-dependent illusions in paintings.

Adult↗
PubMedDate not supplied

[Quality of space perception of moving objects in the aged].

The quality of visual spatial perception for movable objects clearly decreases in old age. This significantly concerns the dynamic visual acuity as well as the dynamic stereoscopy and the parallaktoskopy of motion. The main cause for this is the decrease of the association ability in the CNS during ageing, which leads to the loss of the exact sensomotoricity of the eyes. The senile changes were investigated by the binocular prism rotation device (n = 103) and the parallacto-scopometer (n = 79). The reduction of the dynamic vision in old age is above all important as tho the fitness for traffic.

Adolescent↗