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PubMed2004

Perception of three-dimensional shape from specular highlights, deformations of shading, and other types of visual information.

There have been numerous computational models developed in an effort to explain how the human visual system analyzes three-dimensional (3D) surface shape from patterns of image shading, but they all share some important limitations. Models that are applicable to individual static images cannot correctly interpret regions that contain specular highlights, and those that are applicable to moving images have difficulties when a surface moves relative to its sources of illumination. Here we describe a psychophysical experiment that measured the sensitivity of human observers to small differences of 3D shape over a wide variety of conditions. The results provide clear evidence that the presence of specular highlights or the motions of a surface relative to its light source do not pose an impediment to perception, but rather, provide powerful sources of information for the perceptual analysis of 3D shape.

Depth Perception↗
PubMed1975

Figural after-effects of Köhler and Wallach reinterpreted.

A theory of perception is extended to figural after-effects which has been used already to rationalize the illusory phenomena of static visual illusions, fluctuating figures and visual illusions of motion. The theory proposes three laws of perception. All of the extensive observations of Köhler and Wallach are rationalized under these laws embodying the present theoretical orientation. The theory maintains that the experience of perception occurs only during the interaction of forces introduced by a pattern with the forces characteristic of the brain in order to produce the greatest equilibrium within the two systems of forces. A pattern is not reproduced in the brain. A pattern produces a system of forces. Neither the image of the pattern nor its forces impinging on the nervous system produce the perceptual experience. It is during the process of interaction of the forces of the pattern with the forces of the brain and only during this interaction that perception is experience. This interaction is a constant process to integrate the incompatibilities existing between the two system of forces.

Brain↗
PubMed1979

Relationship between pictorial interpretation and comprehension of three spatial relations in school-age children.

Effects on spatial term comprehension as the result of transformations in the stimulus dimensions of six pictures containing the same three figures were explored using Piaget's concept of spatial perspective. A Modified Test of Pictorial Space (MTPS), adapted from Hudson's (1960) studies on non-Western pictorial perception strategies, was administered to 200 children, aged 6 yrs 5 mos to 11 yrs 3 mos. The purpose of the investigation was to gather data on (1) pictorial interpretation as a function of variations in perceptual depth cue complexity and transformations in conceptual perspective and (2) order of acquisition in the comprehension of two sets of spatial terms referring to perceptual object knowledge and more advanced conceptual knowledge of object relations. Significant age and IQ, but not sex, interactions were found for MTPS performance. Data analyses also supported predicted orders of acquisition and indicated that transformation of conceptual perspective better differentiated among the age span than did either perceptual depth cue complexity or comprehension of spatial terms. Findings are discussed in terms of their methodological and substantive implications for constructing and interpreting pictorially-based language comprehension tasks.

Age Factors↗
PubMed1988

Disparity acceleration effects in stereoscopy and their importance for theoretical neurology.

Stereoscopic perceptions have a special significance for brain modeling, because they require a special form of cortical integration for their appearance. We have newly observed, along ridges of very high stereoscopic disparity accelerations, narrow bands of exaggerated visual depth. These observations signal the importance of local excitation accelerations for future models of brain functions. Some key parameters of disparity acceleration bands are identified and their effects measured.

Cerebral Cortex↗
PubMed1990

Mechanisms underlying the anisotropy of stereoscopic tilt perception.

There is a marked anisotropy in the perception of stereoscopic tilt: vertical gradients of horizontal disparity are more easily perceived than horizontal gradients. This could be explained if orientation disparity (the orientation difference in the two eyes' views of the same line) were one of the cues used to determine tilt, since orientation disparities are in general larger for vertical gradients. We show here that a marked anisotropy in tilt perception is present even with stereograms which contain equally strong orientation disparity cues for horizontal and vertical gradients. This implies that there must be other mechanisms for stereoscopic tilt perception, or further processing steps in the use of orientation disparity, which are anisotropic in their mode of action.

Depth Perception↗
PubMed2000

Electrical multisite stimulation of the isolated chicken retina.

Visual prostheses such as subretinal implants are intended for electrical multisite excitation of the retinal network. To investigate relevant issues like spatial resolution and operational range, we have developed an in vitro method using microelectrode arrays to stimulate isolated retinae. Ganglion cell activity in the chicken retina evoked by distally applied spatial voltage patterns consisted of fast bursts, transient inhibition and delayed discharges, and depended on the amount, location and spatial pattern of the injected charge. The response was altered or disappeared when synaptic transmission was blocked. Our results indicate that shape perception and object location can be partially achieved with subretinal electrical multisite stimulation.

Animals↗
PubMed2000

Local luminance factors that determine the maximum disparity for seeing cyclopean surface shape.

We measured the maximum disparity grating amplitude (d(max)) for seeing cyclopean surface shape, using stereograms made from dense arrays of micropatterns, whose luminance characteristics were manipulated. In Experiment 1, we used disparity gratings made from Gabor micropatterns. D(max) was found to vary inversely both with luminance spatial frequency and with Gabor size, but was constant for a constant bandwidth (frequency times size). To test whether this was due to changes in bandwidth per se or to changes in the number of local features, in Experiment 2 we manipulated the local feature content with a range of micropatterns that we termed 'edgels'. The results supported neither hypothesis. In Experiment 3 we varied the phases of the Fourier components of square wave edgels, thereby introducing more features, and we found that this did not change d(max). Taken together, our results show that d(max) decreases with an increase in the number of local luminance cycles at each luminance scale. D(max) is mainly limited by false target matching between similar components of the micropatterns. Stereopis, in terms of surface shape perception, is served only by first order mechanisms, and only by luminance filters that are broadband.

Depth Perception↗
PubMed2002

Surface construal and the mental representation of scenes.

What distinguishes scenes from nonscenes? Photographs of objects on both naturalistic and blank backgrounds yielded boundary extension (BE: memory for unseen spatial expanse outside the picture's boundaries). However, line-drawn objects on blank backgrounds did not (Experiment 1). Perhaps the blank background was construed as depicting a real-world surface in the photograph condition but was construed as depicting nothing in the line-drawn condition. To change background construal, the authors used objects cut out of photographs; these were placed on blank backgrounds while viewers watched (Experiments 2 and 3). BE was eliminated. The authors propose that amodal continuation is a fundamental aspect of scene perception. However, not all pictures are scenes--only pictures construed as depicting a truncated view of a continuous world.

Adult↗
PubMed1980

Mental imagery and the third dimension.

What sort of medium underlies imagery for three-dimensional scenes? In the present investigation, the time subjects took to scan between objects in a mental image was used to infer the sorts of geometric information that images preserve. Subjects studied an open box in which five objects were suspended, and learned to imagine this display with their eyes closed. In the first experiment, subjects scanned by tracking an imaginary point moving in a straight line between the imagined objects. Scanning times increased linearly with increasing distance between objects in three dimensions. Therefore metric 3-D information must be preserved in images, and images cannot simply be 2-D "snapshots." In a second experiment, subjects scanned across the image by "sighting" objects through an imaginary rifle sight. Here scanning times were found to increase linearly with the two-dimensional separations between objects as they appeared from the original viewing angle. Therefore metric 2-D distance information in the original perspective view must be preserved in images, and images cannot simply be 3-D "scale-models" that are assessed from any and all directions at once. In a third experiment, subjects mentally rotated the display 90 degrees and scanned between objects as they appeared in this new perspective view by tracking an imaginary rifle signt, as before. Scanning times increased linearly with the two-dimensional separations between objects as they would appear from the new relative viewing perspective. Therefore images can display metric 2-D distance information in a perspective view never actually experiences, so mental images cannot simply be "snapshot plus scale model" pairs. These results can be explained by a model in which the three-dimensional structure of objects is encoded in long-term memory in 3-D object-centered coordinate systems. When these objects are imagined, this information is then mapped onto a single 2-D "surface display" in which the perspective properties specific to a given viewing angle can be depicted. In a set of perceptual control experiments, subjects scanned a visible display by (a) simply moving their eyes from one object to another, (b) sweeping an imaginary rifle sight over the display, or (c) tracking an imaginary point moving from one object to another. Eye-movement times varied linearly with 2-D interobject distance, as did time to scan with an imaginary rifle sight; time to tract a point varied independently with the 3-D and 2-D interobject distances. These results are compared with the analogous image scanning results to argue that imagery and perception share some representational structures but that mental image scanning is a process distinct from eye movements or eye-movement commands.

Cues↗
PubMed1998

Stereoscopic visualization of three-dimensional ultrasonic data applied to breast tumours.

OBJECTIVE: This paper presents a technique for stereoscopic visualization applied to three-dimensional (3D) ultrasonic breast data. METHODS: A motorized acquisition system has been designed to translate regularly a linear-phased array transducer, in order to provide a series of parallel echographic slices of the breast. During acquisition, the breast is compressed between a plane support and a plexiglass plate to avoid breast motion. A window in this plate provides access for ultrasonic exploration. From the series of cross-sectional scans, a 3D volume is formed by interpolation between the successive ultrasonic images. A stereoscopic computer-graphic method has been developed to visualize these 3D ultrasonic data. Two conical transparent projections of the volume are computed from two slightly different viewpoints. These two projections make up the stereoscopic pair. This pair is displayed on a stereoscopic monitor for the visualization of the 3D data with the depth dimension. RESULTS: The acquisition system and the method for computing the stereo-echograms were validated using an agar gel phantom. In vivo breast experiments were also performed. CONCLUSION: Visualization of stereo-echographic projections improves the perception of depth and shape of breast tumours.

Breast Diseases↗
PubMed1992

Loss of stereopsis following lesions of cortical areas 17-18 in the cat.

The effects of bilateral removal of cortical areas 17-18 were investigated in the cat; these areas represent the central portion of the visual field and the effect of their removal was evaluated with reference to the perception of Julesz random-dot stereograms. Animals were trained in a two-choice discrimination box to choose between two stereotargets made out of random dots. When appropriately viewed, one produced a vertical rectangle and the other an horizontal one, which appeared to float out in space (crossed stereopsis). The results indicated that all normal cats could solve the random-dot task. Following the cortical lesions, stereoscopic perception was abolished. We also tested for the possibility that this inability to solve the random-dot problem was due to a more general acuity loss. Vernier-type acuity comparing a continuous to a disjointed line showed this to be within the animals' discriminative ability. Offset acuity of the lines was better than that of the stereodot patterns. On the other hand, the ability to determine the preoperatively acquired brightness and pattern discriminations was preserved, although some retraining was necessary for the more difficult patterns. It is therefore suggested that the primary visual cortex, at least in the cat, is involved in the perception of global stereopsis independently of its implication in the discrimination of bidimensional patterns.

Animals↗
PubMed1981

The effect on form perception of change of orientation in the third dimension.

The experiments reported here concern the effect of change of orientation of figures in the third dimension on phenomenal shape. In one experiment, novel two-dimensional wire figures were first shown in one orientation in the sagittal plane, and recognition of them was then tested in an altered orientation in that plane. In another experiment, novel three-dimensional wire figures were first shown in one orientation, and recognition of them was tested following rotation about one of the three major axes of space. The guiding hypotheses were (a) form perception is the end result of a process of figural description; (b) orientation change that alters the perceived location of the top, bottom, and sides of a figure will affect this description; and (c) front-back reversal and rotations about the Y axis will not affect the description because front and back constitute the sides of a figure much as left and right do, and all figural sides are phenomenally equivalent. The findings support these hypotheses except for an unanticipated effect on recognition of 90 degrees rotations about the Y axis. This effect was seen as a hitherto unknown example of egocentrism in perception, since the description is governed by the retinal projection resulting from the particular vantage point of the observer.

Depth Perception↗
PubMed1983

Attentional processing and the subjective contour illusion.

Leading explanations of the subjective contour illusion can be classified as being either "bottom-up" or "top-down." Bottom-up explanations assert that peripheral, physiological mechanisms often associated with the perception of real contours also account for subjective contour (SC) perception. In contrast, top-down explanations posit a more central locus of SC perception and are formulated on a molar, psychological level. A major aspect of bottom-up perceptual processing is that it is largely automatic. On the other hand, top-down processing implies a greater role for selective attention. In an effort to distinguish between bottom-up and top-down accounts of SC perception, the present investigation used a dual-task paradigm to test the relative attentional demands of real contour perception versus SC perception. In the primary task, subjects made speeded same-different discriminations of either paired SC forms or their real contour analogues. Half the subjects performed this primary task in conjunction with a six-digit short-term memory load secondary task. If subjective forms indeed impose a greater limited-capacity processing load than real forms, then the need to share processing capacity with a secondary task was expected to produce a greater increment in reaction time (RT) for subjective relative to real forms. The results indicated that the expected enhanced RT increment for subjective relative to real forms with the addition of a concurrent memory load was limited to same trials. This result implies that the nature of response indicators must be considered in assessing capacity requirements with the sort of dual-task paradigm used in the present investigation. Nevertheless, the fact that the increment in same RT with the addition of a concurrent memory load was greater for subjective relative to real forms accords with expectations derived from the notion that the perception of SCs is more attention demanding than that of real contours. If the interpretation of the present study is correct, then a comprehensive theory of SC perception will most likely be formulated within the top-down perspective of conceptually driven visual information processing.

Adult↗
PubMed1994

Apparent motion determined by surface layout not by disparity or three-dimensional distance.

The most meaningful events ecologically, including the motion of objects, occur in relation to or on surfaces. We run along the ground, cars travel on roads, balls roll across lawns, and so on. Even though there are other motions, such as flying of birds, it is likely that motion along surfaces is more frequent and more significant biologically. To examine whether events occurring in relation to surfaces have a preferred status in terms of visual representation, we asked whether the phenomenon of apparent motion would show a preference for motion attached to surfaces. We used a competitive three-dimensional motion paradigm and found that there is a preference to see motion between tokens placed within the same disparity as opposed to different planes. Supporting our surface-layout hypothesis, the effect of disparity was eliminated either by slanting the tokens so that they were all seen within the same surface plane or by inserting a single slanted background surface upon which the tokens could rest. Additionally, a highly curved stereoscopic surface led to the perception of a more circuitous motion path defined by that surface, instead of the shortest path in three-dimensional space.

Depth Perception↗
PubMed1987

The recovery of structure from motion: no evidence for a special link with the convergent disparity mechanism.

Convergent and divergent stereo mechanisms were compared in their ability to recover structure from motion. Contrary to a recent result reported by Richards and Lieberman, no difference in their performance was found; both mechanisms appeared equally capable of supporting the perception of good structure from motion. Possible reasons for the disparate results are discussed.

Attention↗
PubMed1994

The visual perception of three-dimensional shape from self-motion and object-motion.

To evaluate the influence of egomotion on the three-dimensional visual processing of structure-from-motion (SFM), we compared the visual discrimination between planar and spherical surfaces during subject-translation, object-translation, or rotation of the object in depth. Performance was the best for object-rotation, intermediate for subject-translation, and the poorest for object-translation--and thus increased with the quality of retinal image stabilization achieved in the different conditions. This suggests that the major role of self-motion information was to stabilize retinal images. In view of previous results, we propose that the interactions between self-motion information and SFM are reduced to functional complementarity, in the sense that self-motion can lift visual ambiguities but does not improve the sensitivity of SFM processes.

Adult↗
PubMed2004

Line at shape-from-shadow border tested with stereo.

Kennedy and Bai (2000 Perception 29 399-408) argued incorrect border polarity blocked perception of faces in shape-from-shadow 'Mooney faces' with dark lines at the contour, a display inspired by Hering. Their hypothesis was tested with several displays, notably binocular gratings made of lines of dots. The stereo-induced depth involved a shadow falling on two surface planes. Most of a dark-dotted (shadow) region appeared to be on one surface, but a strip of dark dots at the shadow's border appeared to be on another-to the fore or rear. Control conditions involved 'negative' images (white dots). Subjects saw the shadowed object as easily in dark-dotted images with stereo depth as in an image with uniform depth for all the dots, and more readily than in the negatives. Our results favour the border-polarity hypothesis.

Adult↗