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PubMed1995

Cross-modal slant and curvature matching of stereo- and motion-induced surfaces.

In many laboratory setups and in many day-to-day situations, a unique solution of the structure-from-two-views problem is unobtainable. Yet, when the visual system is presented with two projections in a sequence, it nevertheless appears to generate a reasonably stable percept of structure. In the research reported here, we examined whether the same surface would be perceived when subjects were presented with a pair of views that alternated in time monocularly (two-frame motion) or were shown simultaneously to both eyes (stereo). In Experiment 1, we studied slant perception: human observers were asked to match the slant of a motion-induced planar surface with its stereo-induced counterpart. In Experiment 2, the perceived curvature of parabolic surfaces was matched in a similar way. The results show that motion-induced slant is matched with a higher value of the stereo-induced slant. However, the curvature experiment showed that motion-induced curvature is matched with a lower stereo-induced curvature. One possible explanation may be that the slant and curvature are internally inconsistent in at least one of the modalities.

Attention↗
PubMed1996

Role of optical flow field asymmetry in the perception of heading during linear motion.

During linear translation through a stationary environment, the pattern of optical flow generated on each retina is symmetrical when the head is aligned with the heading, but during lateral gaze the optical flow is asymmetric. We assessed whether human subjects could use the magnitude of this asymmetry to determine the direction of heading during passive translation through a 3-D environment. When allowed to move their heads in order to look in the direction of self-motion, subjects indicated their heading precisely and accurately. When the head was locked in alignment with the misaligned body, and gaze adjustments were not allowed, responses were quite precise, but showed a large bias which increased with increasing heading angle.

Adult↗
PubMed2003

Leonardo's constraint: two opaque objects cannot be seen in the same direction.

Given Leonardo's constraint that 2 opaque objects cannot be seen in the same direction, how are the regions of objects occluded to 1 eye included in perception? To answer this question, the authors presented 3-dimensional stimuli, similar to the ones that concerned Leonardo, and measured the visual directions of their monocular and binocular regions. When the distance between near and far objects was large, the nonfixated object was seen as double and blurry. Leonardo's constraint was met by seeing the near object as double and transparent or the distant object as double and superimposed. When the distance between near and far objects was small, the constraint was met by a perceptual displacement and compression of parts of the nonfixated object.

Depth Perception↗
PubMed1996

Investigating shape-from-shading illusions using solid objects.

Recent growth in the shape-from-shading psychophysics literature has been paralleled by an increasing availability of computer graphics hardware and software, to the extent that most psychophysical studies in this area now employ computer lighting algorithms. The most widely used of these algorithms in shape-from-shading psychophysics is the Phong lighting model. This model, and other shading models of its genre, produce readily interpretable images of three-dimensional scenes. However, such algorithms are only approximations of how light interacts with real objects in the natural environment. Nevertheless, the results from psychophysical experiments using these techniques have been used to infer the processes underlying the perception of shape-from-shading in natural environments. It is important to establish whether this substitution is ever valid. We report a series of experiments investigating whether two recently reported illusions seen in computer-generated, Phong shaded images occur for solid objects under real illuminants. The two illusions investigated are three-dimensional curvature contrast and the illuminant-position effect on perceived curvature. We show that both effects do occur for solid objects, and that the magnitude of these effects are equivalent regardless of whether subjects are presented with ray traced or solid objects.

Algorithms↗
PubMed1995

Growth and behavioral effects of early postnatal chromium and manganese exposure in herring gull (Larus argentatus) chicks.

Organisms in marine environments are exposed to chromium and manganese, yet little is known of the effects of these metals on physiology and behavior. In this article we examine the effects of chromium and manganese on early neurobehavioral development in herring gulls, Larus argentatus. Each of 36 2-day-old herring gull chicks was randomly assigned to one of three treatment groups to receive either chromium nitrate (25 mg/kg), manganese acetate (50 mg/kg), or a control dose of sterile saline solution. The trios were not siblings, but were matched by age and weight. Behavioral tests examined food-begging, balance, locomotion, righting response, recognition, thermoregulation, and perception. There were significant differences in begging behavior by 5 days postinjection, and there were significant differences in weight gain throughout development until 50 days of age, when the experiment was terminated. Behavioral tests, administered from 18-48 days postinjection, indicated significant differences between control and the exposed groups for time to right themselves; thermoregulation behavior; and performance on a balance beam, inclined plane, actual cliff, and visual cliff (although not all components varied significantly). Of the 14 behavioral measures with significant differences, control birds performed best on 12.

Analysis of Variance↗
PubMed1994

Lightness perception can be affected by surface curvature from stereopsis.

It is demonstrated that lightness perception can be affected by shape from stereopsis. The starting point was a report by Knill and Kersten that the perceived lightness of a monocularly viewed surface can be affected by outline-contour cues indicating that the surface is three-dimensional (3-D). In that study stimuli consisted of two equally sized abutting regions each having the same vertical linear-intensity ramp, so that the horizontal abutting boundary of the two patches created a sharp change in intensity. When this version of the Craik-O'Brien-Cornsweet stimulus has a rectangular outline, it exhibits the standard simultaneous contrast illusion: equivalent patches in the top and bottom regions appear to have different brightness despite having the same luminance. Knill and Kersten replicated this phenomenon with stimuli whose outline-contour cues were consistent with a flat (planar) surface. They found, however, that the illusion was greatly reduced in stimuli with outlines consistent with two abutting 3-D quarter cylinders, for which equivalent regions in the two halves appeared of similar lightness. Knill and Kersten interpreted this effect in terms of surface-lightness computations that took into account 3-D surface shape to achieve an integrated interpretation of the luminance and shape data. In the present report three experiments are described for which these earlier findings were taken as the starting point. In the first experiment the results were replicated by the use of a different methodology. In the second experiment it was shown that shape-from-stereo can produce similar effects on lightness perception to that caused by shape-from-contour. Real 3-D objects with curved surfaces, luminance profiles of the Knill and Kersten type, and carefully controlled outline-contour cues were used so that the objects appeared flat when viewed monocularly but curved in 3-D when seen binocularly. The third experiment was a control confirming that the stereo effect was not simply due to differences caused by monocular versus binocular viewing. It is concluded that the human visual system uses stereo cues, as well as outline-contour cues, in the interpretation of luminance data to recover surface lightness.

Adult↗
PubMed2005

Remote effects of highlights on gloss perception.

The perception of a glossy surface in a static monochromatic image can occur when a bright highlight is embedded in a compatible context of shading and a bounding contour. Some images naturally give rise to the impression that a surface has a uniform reflectance, characteristic of a shiny object, even though the highlight may only cover a small portion of the surface. Nonetheless, an observer's impression of gloss may be partial and nonuniform at image regions outside of a highlight. A rating scale and small probe points indicating image locations were used to investigate the differential perception of gloss within a single object. Gloss ratings given by observers were not uniform across a surface, but decreased as a function of distance from a highlight. When, by design, the distance from a highlight was uncoupled from the luminance value at corresponding probe points, the decrease in rated gloss correlated more with distance than with luminance change. Experiments also indicated that gloss ratings may change as a function of estimated surface distance, rather than as a function of image distance. Surface continuity affected gloss ratings, suggesting that surface and gloss processing are closely related.

Analysis of Variance↗
PubMed1986

Testing visual perception of three-dimensionally moving objects (dynamic stereoscopy).

In the past decade, visual requirements in the field of stereoscopy have considerably increased in a number of professions, as well in present-day traffic and sports. As a result of a statement of the WHO (1984) viz. that for prevention of accidents the testing of static vision only is insufficient, and that dynamic vision too should be a subject of investigation, a test for measuring dynamic stereoscopic visual acuity has been devised. With the help of two synchronously rotating prisms, a stereo test consisting of four bars is transposed into an apparent circumduction movement which is presented at different velocities. Stereoscopy under static and dynamic conditions do not run a parallel course. Dynamic stereoscopy is significantly influenced by age, but not by sex.

Adult↗
PubMed1980

[Decreasing local stereopsis with increasing horizontal disparity, indicating decreasing density of binocular cortical projection towards the limits of Panum's area (author's transl)].

Measuring local stereopsis by means of random dot stereograms with increasing horizontal disparity, the relative density of binocular cortical projection has been determined at a distance of 75 min of arc from the fovea. The accuracy of stereoscopic perception decreased with increasing horizontal disparity. The reciprocal value of the error frequency was used to measure the density of binocular cortical projection. Panum's area at the above mentioned distance from the fovea can be constructed by plotting the error frequency against the horizontal disparity. We observed a decrease of the relative density of binocular cortical projection towards the limits of Panum's area without a sharp break. The results are in agreement with those reported by Bishop and Henry and Joshua in the cat (receptive field disparity). The theory of stereopsis as proposed by Bishop explains our findings well and may be transferred to binocular vision in man.

Depth Perception↗
PubMed1996

Perceiving motion and rigid structure from optic flow: a combined weak-perspective and polar-perspective approach.

Structure-from-motion algorithms based on weak-perspective projection have many interesting properties and could serve as a basis for a model of human perception of motion and structure from motion (M&SFM). There is some psychophysical evidence, however, that points to discrepancies between what can be accomplished with these algorithms and the performance of human subjects in certain M&SFM tasks. In light of this evidence, this paper presents a mechanism that both takes advantage of all the possibilities offered by a weak-perspective approach and behaves in a manner that is in close correspondence with human performance in M&SFM tasks. It consists of a novel weak-perspective-based method operating at small visual angles and a complementary, perspective-projection-based method operating at larger visual angles.

Algorithms↗
PubMed2005

The Necker cube--an ambiguous figure disambiguated in early visual processing.

How can our percept spontaneously change while the observed object stays unchanged? This happens with ambiguous figures, like the Necker cube. Explanations favor either bottom-up factors in early visual processing, or top-down factors near awareness. The EEG has a high temporal resolution, so event related potentials (ERPs) may help to throw light on these alternative explanations. However, the precise point in time of neural correlates of perceptual reversal is difficult to estimate. We developed a paradigm that overcomes this problem and found an early (120 ms) occipital ERP signal correlated with endogenous perceptual reversal. Parallels of ambiguous-figure-reversal to binocular-rivalry-reversals are explored.

Adult↗
PubMed1990

Emmert's law in the Ames room.

The Ames distorted room illusion, in which the perceived sizes of objects placed within the room differ from their objective sizes, has been used to support arguments for indirect perception. A study is reported in which Emmert's law of the apparent size of after-images was examined in relation to the Ames room's illusory alteration of apparent and actual distances. Size judgments of afterimages projected into the Ames room were compared with control conditions in which both actual and apparent afterimage projection distances were reproduced. Results indicate that Emmert's law may not provide a simple geometrical relationship between proximal image size and actual viewing distance, and that the processes involved in making afterimage size judgments are similar to those processes involved in making size judgments of 'real world' objects.

Adult↗
PubMed1993

Independent effects of lighting, orientation, and stereopsis on the hollow-face illusion.

Three experiments were conducted to investigate factors contributing to the 'hollow face' illusion. A novel method was employed in which the distance from the mask at which the illusion became apparent or disappeared, when retreating or approaching, respectively, was taken as a measure of the strength of the illusion. In all the experiments an effect of direction of observer's movement was found, demonstrating the stability of the initial percept. Upright orientations were compared with inverted ones to investigate if the illusion reflects a bias towards a familiar percept. The direction of lighting was also varied. Independent main effects of orientation and lighting were found to be consistent with preferences both for upright faces and for top lighting. However, inverted faces also produced the illusion to some extent, suggesting a general preference for convexity. The role of stereopsis in resolving the illusion was tested by comparing monocular with binocular viewing conditions. Monocular viewing conditions gave rise to shorter distances, suggesting that the retinal disparities available with binocular viewing are important in disambiguating the illusion at small distances. The results are interpreted within the framework of a 2 1/2-dimensional sketch derived from independent modular processing of visual information.

Depth Perception↗
PubMed1975

Transformations of consciousness. A cartography. I. The perception-hallucination continuum.

Self-awareness emerges from the evolutionary transformation of material structures into magical, mythical and mental structures of consciousness. Western varieties of conscious states may be mapped on a perception-hallucination continuum of increasing ergotropic or hyper-arousal. These levels of subcortical arousal are cortically or cognitively interpreted as normal, creative, hyperhrenic, cataleptic and ecstatic states. During increasing hyper-arousal (characterized by EEG desynchronization): (1) the variability of the EEG amplitude decreases in introverts whereas in extroverts, it increases; (2) exteroception is transformed into an experience of interoception, while willed motor activity becomes increasingly impaired and ultimately inhibited, and (3) information processing during these hallucinatory states is preferentially shifted from the speech dominant and motor-coordinating or "major" toward the nonverbal, gestalt-perceiving, the non-dominant or "minor" cortical hemisphere.

Amnesia↗
PubMed1975

[Spatial value of the fovea in young children].

After defining physiological fixation of the fovea and relating our knowledge of its normal development in the context of spatial perception, we have reviewed the pathological adaptations encountered in strabismus. Out of all the clinical examinations that are possible in very young children and which enable sensory disturbances to be revealed, the examination of fixation appears to be simple and dependable, sometimes well before the appreciation of the comparaison of visual acuity of the two eyes. Amblyopia can be suspected using this method in cases of poor foveal fixation when compared with the other eye, and it enables treatment to be instituted and controlled all the more efficiently since therapy in an early stage can lead to a rapid recovery and maintenance of normal development.

Amblyopia↗
PubMed1988

Additivity, subadditivity, and the use of visual information: a reply to Massaro (1988).

Previously we (Bruno & Cutting, 1988) explored the perception of spatial relations among objects laid out in a computer-generated environment. In his commentary on our article, Massaro (1988) raised several issues. The most important is from his reanalysis, which indicated that--because of a subadditive trend in the results--additive and multiplicative strategies fit our data in Experiment 1 about equally well. In reply, we performed a different analysis. Results corroborate subadditivity--and hence multiplicative information combination--in Experiment 1 but provide no evidence for it in Experiments 2 and 3. On the whole, then, the results still support additivity more strongly than any other combination rule and thus support our notion of minimodularity.

Depth Perception↗
PubMed1991

The object-detection effect: configuration enhances perception.

Line drawings used by Weisstein and Harris (1974) are seen as box-like three-dimensional figures if the lines are arranged properly. A flat two-dimensional pattern is seen when these same lines are disarranged. A target line contained within the three-dimensional figure is identified more readily than is the same line contained within a two-dimensional figure. This finding was extended in the present experiments: The three-dimensional stimulus was detected more quickly than the two-dimensional stimulus, under conditions of visual backward masking. Three-dimensional stimuli were also classified more quickly than two-dimensional stimuli. Just as with the face-detection effect and the word-detection effect, object detection can be affected by the form of the visual stimulus.

Adult↗
PubMed1995

The functional architecture of human visual motion perception.

UNLABELLED: A powerful paradigm (the pedestal-plus-test display) is combined with several subsidiary paradigms (interocular presentation, stimulus superpositions with varying phases, and attentional manipulations) to determine the functional architecture of visual motion perception: i.e. the nature of the various mechanisms of motion perception and their relations to each other. Three systems are isolated: a first-order system that uses a primitive motion energy computation to extract motion from moving luminance modulations; a second-order system that uses motion energy to extract motion from moving texture-contrast modulations; and a third-order system that tracks features. Pedestal displays exclude feature-tracking and thereby yield pure measures of the first- and second-order systems which are found to be exclusively monocular. Interocular displays exclude the first- and second-order systems and thereby to yield pure measures of feature-tracking. RESULTS: both first- and second-order systems are fast (with temporal frequency cutoff at 12 Hz) and sensitive. Feature tracking operates interocularly almost as well as monocularly. It is slower (cutoff frequency is 3 Hz) and it requires much more stimulus contrast than the first- and second-order systems. Feature tracking is both bottom-up (it computes motion from luminance modulation, texture-contrast modulation, depth modulation, motion modulation, flicker modulation, and from other types of stimuli) and top-down--e.g. attentional instructions can determine the direction of perceived motion.

Attention↗