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PubMed2000

Mechanisms for seeing transparency-from-motion and orientation-from-motion.

Structure-from-motion (SFM) perception is hypothesised to be mediated by units that sense the near-far relationships in transparency-from-motion (TFM) and orientation-from-motion (OFM). The frequency of subjective reversals during observation of ambiguous SFM displays is considerably decreased when either the direction of rotation or the surface orientation is oscillated during the inspection. Such manipulations impede adaptation of units selectively sensitive to TFM and OFM. The results show that both OFM and TFM units are direction-selective, and that the reversal rate is unaffected by reducing TFM to zero; and support the view that depth order, when both TFM and OFM are present, is estimated by common neural units.

Adaptation, Physiological↗
PubMed2004

Pointing out of the picture.

The eyes of portrayed people are often noticed to 'follow you' when you move with respect to a flat painting or photograph. We investigated this well-known effect through extensive measurements of pictorial relief and apparent orientation of the picture surface for a number of viewing conditions, including frontal and oblique views. We conclude that cases of both oblique and frontal viewing are very similar in that perception simply follows what is indicated by the proximal stimulus, even though this may imply that the (perceived) physical and pictorial spaces segregate. The effect of foreshortening then causes an apparent narrowing of pictorial objects. We find no evidence for any 'correction' mechanisms that might be specifically active in oblique viewing conditions.

Depth Perception↗
PubMed2005

Dissociation between visual perception of allocentric distance and visually directed walking of its extent.

Walking without vision to previously viewed targets was compared with visual perception of allocentric distance in two experiments. Experimental evidence had shown that physically equal distances in a sagittal plane on the ground were perceptually underestimated as compared with those in a frontoparallel plane, even under full-cue conditions. In spite of this perceptual anisotropy of space, Loomis et al (1992 Journal of Experimental Psychology. Human Perception and Performance 18 906-921) found that subjects could match both types of distances in a blind-walking task. In experiment 1 of the present study, subjects were required to reproduce the extent of allocentric distance between two targets by either walking towards the targets, or by walking in a direction incompatible with the locations of the targets. The latter condition required subjects to derive an accurate allocentric distance from information based on the perceived locations of the two targets. The walked distance in the two conditions was almost identical whether the two targets were presented in depth (depth-presentation condition) or in the frontoparallel plane (width-presentation condition). The results of a perceptual-matching task showed that the depth distances had to be much greater than the width distances in order to be judged to be equal in length (depth compression). In experiment 2, subjects were required to reproduce the extent of allocentric distance from the viewing point by blindly walking in a direction other than toward the targets. The walked distance in the depth-presentation condition was shorter than that in the width-presentation condition. This anisotropy in motor responses, however, was mainly caused by apparent overestimation of length oriented in width, not by depth compression. In addition, the walked distances were much better scaled than those in experiment 1. These results suggest that the perceptual and motor systems share a common representation of the location of targets, whereas a dissociation in allocentric distance exists between the two systems in full-cue conditions.

Adult↗
PubMed1993

Infant use of relative motion as information for form: evidence for spatiotemporal integration of complex motion displays.

Previous studies of infants' ability to integrate and to utilize relative motion as information for form in the absence of structural cues have primarily involved motions that are uniform in rate, direction, and path within the form to be constructed. In the present study, we examined infants' ability to integrate relative motion information from motions that are nonuniform along these dimensions, and from this integrative process to construct a coherently rotating two-dimensional form. Infants' ability to integrate nonuniform motion was measured with regard to their ability to discriminate the rotating form from a noncoherent control display containing the same absolute motions. The results showed that discrimination of the coherent and incoherent displays was not demonstrated until 7 months of age. Two additional experiments were conducted to rule out the possibility that this discrimination was based on the detection of local regions of coherence, rather than the perception of the global rotating form. In both experiments, the results did not support discrimination based exclusively on local cues alone. From the combined results of all three experiments, we conclude that infants demonstrate the capacity to integrate the information contained within nonuniform trajectories into a coherent structure by 7 months of age.

Age Factors↗
PubMed1999

[Peter Ludvig Panum's sensory physiological works from his years in Kiel 1853-1864].

In 1858 Panum published a monography on "Physiologische Untersuchungen über das Sehen mit zwei Augen". He proposed the concept of corresponding circles of perception instead of the absolute identity of corresponding points on the retina. This was met with opposition particularly by A. W. Volkmann of Halle who tried to explain psychologically all stereoscopic phenomena (Arch. Ophthalmol., 1859). Both authors defended their views with numerous experiments. Panum's results in "Uber einheitliche Verschmelzung verschiedenartiger Netzhauteindrücke beim Sehen mit zwei Augen" (Arch. Anatomie, 1861) is still valid today.

Depth Perception↗
PubMed2000

Representation of stereoscopic edges in monkey visual cortex.

Form perception in random-dot stereograms is based on information that resides in the correlation between the two images, but is not present in either image alone. We have studied the coding of stereoscopic figures in the neural activity of areas V1 and V2 of alert behaving monkeys. While cells in V1 generally responded according to the disparity of the surface at the receptive field, we found cells in area V2 that responded selectively to the figure edges. These cells signaled the location and orientation of contrast borders as well as stereoscopic edges, and were often selective for the direction of the step in depth. We concluded that stereoscopic edges are explicitly represented in area V2.

Animals↗
PubMed2005

Depth and motion in historical descriptions of motion parallax.

Motion parallax was described as a cue to depth over 300 years ago and as producing apparent motion over 150 years ago. In recent years, experimental interest in motion parallax has increased, following the rediscovery of the idea that stimulus motion can be yoked to head movement. We compare the historical descriptions with some contemporary research, which indicates how depth and motion perception are dependent on the conditions of stimulation.

Depth Perception↗
PubMed1992

Surface perception in pictures.

Subjects adjusted a local gauge figure such as to perceptually "fit" the apparent surfaces of objects depicted in photographs. We obtained a few hundred data points per session, covering the picture according to a uniform lattice. Settings were repeated 3 times for each of 3 subjects. Almost all of the variability resided in the slant; the relative spread in the slant was about 25% (Weber fraction). The tilt was reproduced with a typical spread of about 10 degrees. The rank correlation of the slant settings of different observers was high, thus the slant settings of different subjects were monotonically related. The variability could be predicted from the scatter in repeated settings by the individual observers. Although repeated settings by a single observer agreed within 5%, observers did not agree on the value of the slant, even on the average. Scaling factors of a doubling in the depth dimension were encountered between different subjects. The data conformed quite well to some hypothetical fiducial global surface, the orientation of which was "probed" by the subject's local settings. The variability was completely accounted for by single-observer scatter. These conclusions are based upon an analysis of the internal structure of the local settings. We did not address the problem of veridicality, that is, conformity to some "real object."

Attention↗
PubMed2000

Perception of three-dimensional shape from texture is based on patterns of oriented energy.

This paper presents empirical support for a new observer model of inferring three-dimensional shape from monocular texture cues. By measuring observers' abilities to estimate the relative three-dimensional curvature along a textured surface from two-dimensional projected images, and concurrently examining the local spectral changes occurring in the projected image for various texture patterns, we have found that correlated changes in oriented energy along lines corresponding to the lines of maximum and minimum curvature of the surface are crucial for conveying the three-dimensional shape of the surface. Energy along these lines of maximum and minimum curvature can be used to compute the orientation of local surface patches. Texture patterns consisting of simple and complex sinusoidal gratings and plaids, and filtered noise were drawn onto a surface that was corrugated sinusoidally in depth about the horizontal axis and projected in perspective onto an image plane. The perceived relative surface curvature was reconstructed from measurements of local ordinal depth around a central fixation point at 12 different phases of the corrugation. Our results show that: (1) it is neither necessary nor sufficient to identify individual texture elements or texture gradients in order to extract the shape of the surface; (2) one-dimensional frequency modulation is insufficient for conveying complex three-dimensional shape. (3) Veridical ordinal depth is seen only when the projected pattern contains changes in oriented energy along lines corresponding to projected lines of maximum curvature of the surface. (4) For a surface corrugated in depth about the horizontal axis, this pattern of oriented energy arises from energy along the vertical direction in the global Fourier transform of the pre-corrugated pattern. (5) Local orientation changes across lines of minimum curvature can be also critical for conveying shape. (6) These correlated orientation changes along lines of maximum and minimum curvature are entirely lost in parallel projection. Hence texture is a useful cue for shape if the image is a perspective projection. (7) Only some natural textures will provide sufficient monocular cues to support veridical shape inferences, and this can be predicted from their global Fourier transforms.

Computer Simulation↗
PubMed1995

Integration by association: combining three-dimensional cues to extrinsic surface shape.

Surface shape is visually derived from multiple sources of three-dimensional (3-D) information. The apparent unity of the percept creates an assumption that there are perceptual processes that resolve and combine the different channels of information within some common 3-D representation. However, integration by the explicit conversion of the information from different sources into a common representation is computationally difficult and unnecessary. An alternative, integration by association, is discussed and related to a variety of experimental results on 3-D-cue conflict.

Association↗
PubMed2006

Binocular interactions in patients with age-related macular degeneration: acuity summation and rivalry.

This study examined two aspects of binocular function in patients with age-related macular degeneration (AMD): summation/inhibition of visual acuity and rivalry. The performance of 17 patients with AMD was compared with that of 17 elderly controls and 21 young people. Monocular and binocular acuities were measured using a multiple-E optotype test. Binocular ratios, defined as the better-eye acuity divided by the binocular acuity, were calculated. We also measured eye dominance during rivalry (proportion of time the participants reported perceiving the input to each eye) and rivalry rates (number of alternations per minute). The results showed that while overall binocular ratios were similar for the three groups, the frequency distributions of people who experienced inhibition, equality or summation were different for the young and AMD groups. In the rivalry test, patients experienced more piecemeal perception than the elderly and young controls, but time dominance from the better-seeing eye was comparable for the three groups. Rivalry rates decreased with age and further with pathology. Moreover, rivalry time dominance of the worse-seeing eye was negatively correlated with interocular acuity differences for the AMD group.

Adult↗
PubMed1998

The objects of action and perception.

Two major functions of the visual system are discussed and contrasted. One function of vision is the creation of an internal model or percept of the external world. Most research in object perception has concentrated on this aspect of vision. Vision also guides the control of object-directed action. In the latter case, vision directs our actions with respect to the world by transforming visual inputs into appropriate motor outputs. We argue that separate, but interactive, visual systems have evolved for the perception of objects on the one hand and the control of actions directed at those objects on the other. This 'duplex' approach to high-level vision suggests that Marrian or 'reconstructive' approaches and Gibsonian or 'purposive-animate-behaviorist' approaches need not be seen as mutually exclusive, but rather as complementary in their emphases on different aspects of visual function.

Animals↗
PubMed2003

Voluntary head movement and allocentric perception of space.

Although visual input is egocentric, at least some visual perceptions and representations are allocentric, that is, independent of the observer's vantage point or motion. Three experiments investigated the visual perception of three-dimensional object motion during voluntary and involuntary motion in human subjects. The results show that the motor command contributes to the objective perception of space: Observers are more likely to apply, consciously and unconsciously, spatial criteria relative to an allocentric frame of reference when they are executing voluntary head movements than while they are undergoing similar involuntary displacements (which lead to a more egocentric bias). Furthermore, details of the motor command are crucial to spatial vision, as allocentric bias decreases or disappears when self-motion and motor command do not match.

Awareness↗
PubMed1997

Extraretinal eye position signals determine perceived target location when they conflict with visual cues.

To examine the role of extraretinal eye position information (EEPI) in visual perception of target location in normal room illumination, subjects participated in experiments in which EEPI was manipulated using the eye press maneuver with either monocular or binocular viewing. The viewing condition and eye press caused EEPI and retinal information about target location to conflict. Pointing responses in eye press trials were all in the direction of EEPI showing that EEPI is the dominant source of information in egocentric visual space perception. In binocular viewing, version and vergence occur in response to the eye press to maintain fusion and EEPI based on these movements also determine perceived location. An unanticipated finding was that the eye press was variable in its effectiveness in rotating the eye, which contributed to large variability in pointing errors and suggested the method would be a poor choice for future work.

Adult↗
PubMed1984

Infants' perception of pictorially specified interposition.

Five- and seven-month-olds were tested for sensitivity to pictorial interposition in two experiments. Reaching was used as the dependent measure. Seven-month-olds gave evidence of sensitivity to pictorial interposition. In both experiments they showed a significant preference to reach for the pictorially nearer side of a flat interposition display which stimulated three overlapping surfaces and showed no reaching preferences when viewing control displays. Five-month-olds' reaching tendencies did not differ significantly between experimental (interposition) and control conditions in the second experiment. This result indicated that their responses may have been due to nonspatial proximal stimulus variables in the displays. Five-month-olds, therefore, gave no evidence of sensitivity to pictorial interposition. The finding that 7-month-olds are sensitive to pictorial interposition and the failure to find sensitivity in 5-month-olds is consistent with findings from other studies on infants' sensitivity to pictorial depth information. The cumulative results of these studies suggest that sensitivity to pictorial depth information first appears between 5 and 7 months of age.

Child Development↗
PubMed2004

The visual perception of length along intrinsically curved surfaces.

The ability of observers to perceive three-dimensional (3-D) distances or lengths along intrinsically curved surfaces was investigated in three experiments. Three physically curved surfaces were used: convex and/or concave hemispheres (Experiments 1 and 3) and a hyperbolic paraboloid (Experiment 2). The first two experiments employed a visual length-matching task, but in the final experiment the observers estimated the surface lengths motorically by varying the separation between their two index fingers. In general, the observers' judgments of surface length in both tasks (perceptual vs. motoric matching) were very precise but were not necessarily accurate. Large individual differences (overestimation, underestimation, etc.) in the perception of length occurred. There were also significant effects of viewing distance, type of surface, and orientation of the spatial intervals on the observers' judgments of surface length. The individual differences and failures of perceptual constancy that were obtained indicate that there is no single relationship between physical and perceived distances on 3-D surfaces that is consistent across observers.

Depth Perception↗
PubMed2006

Pushing the limits of transparent-motion detection with binocular disparity.

When transparent motion is defined purely by direction differences, observers fail to detect more than two signal directions simultaneously [Edwards, M., & Greenwood, J.A. (2005). The perception of motion transparency: A signal-to-noise limit. Vision Research, 45, 1877-1884]. This limit is strongly related to signal-detection thresholds for transparent motion, which are several times higher than uni-directional thresholds. When the effective signal intensities are elevated by speed differences that drive independent global-motion systems, the transparent-motion limit can be extended to allow detection of three signals [Greenwood, J.A., & Edwards, M. (2006). An extension of transparent-motion detection limit using speed-tuned global-motion systems. Vision Research, 46, 1440-1449]. Because there are independent disparity-tuned global-motion systems, distributing transparent-motion signals across distinct depth planes also allows an increase in their effective signal intensity. In the present study, the addition of depth differences enabled the simultaneous detection of three signals. However, as with the addition of speed differences, observers were not able to detect four signals, which would be predicted if signal intensity were the sole constraint on transparent-motion detection. The combination of depth and speed produced similar results, suggesting that there is a strict higher-order limit, possibly related to attention, restricting the maximum number of signals that can be detected simultaneously to three.

Depth Perception↗
PubMed1999

Computational analysis of disparity modulation sensitivity: an explanation in terms of a Bayesian surface reconstruction.

Sensitivity to binocular disparity modulation has been shown to have a bandpass nature. This paper presents a computational account for the disparity modulation function (DMF) in terms of a Bayesian surface reconstruction. The Bayesian approach suggests that prior assumptions about surface structure will affect the perception of disparity modulation. Taking into account a prior constraint of surface smoothness being imposed on the perceived surfaces, we propose that computing the first derivatives of the surfaces determines the bandpass shape of the DMF. Based on this idea, we derive an analytical prediction of the DMF. It is then shown that the prediction gives a good fit to the empirical data. Implications for possible mechanisms underlying the DMF are discussed.

Depth Perception↗