The experiments reported herein probe the visual cortical mechanisms that control near–far percepts in response to two-dimensional stimuli. Figural contrast is found to be a principal factor for the emergence of percepts of near versus far in pictorial stimuli, especially when stimulus duration is brief. Pictorial factors such as interposition (Experiment 1) and partial occlusion Experiments 2 and 3) may cooperate, as generally predicted by cue combination models, or compete with contrast factors in the manner predicted by the FACADE model. (...) In particular, if the geometrical conŽ guration of an image favors activation of cortical bipole grouping cells, as at the top of a T-junction, then this advantage can cooperate with the contrast of the conŽ guration to facilitate a near–far percept at a lower contrast than at an X-junction. Varying the exposure duration of the stimuli shows that the more balanced bipole competition in the X-junction case takes longer exposure times to resolve than the bipole competition in the T-junction case (Experiment 3). (shrink)

Ducklings were placed either singly or in pairs on a platform at two different heights. Both height and pairing influenced performance: More ducklings descended from the platform at low heights, and more single ducklings descended than paired ducklings. The social factor, pairing, made behavior more cautious and decreased the number of distress calls. A similar trend for pairing to influence performance was shown on the visual cliff. Without its peers, the duckling is a distressed animal. Previous careless behavior by ducklings (...) on the visual cliff may be ascribed to testing the ducklings outside their normal social environment. (shrink)

The Greenough stereomicroscope, or “Stemi” as it is colloquially known among microscopists, is a stereoscopic binocular instrument yielding three-dimensional depth perception when working with larger microscopic specimens. It has become ubiquitous in laboratory practice since its introduction by the unknown scientist Horatio Saltonstall Greenough in 1892. However, because it enabled new experimental practices rather than new knowledge, it has largely eluded historical and epistemological investigation, even though its design, production, and reception in the scientific community was inextricably (...) connected to the new epistemological ideals of the life sciences caught between natural history and modern science. The development of the microscope will be contextualized within the scientific and technological landscape, showing how Greenough navigated his way through this terrain, and what led him to sow the seeds for the stereoscopic microscope. The historical controversy over the optical mechanism, through which the instrument would generate the desired depth perception, and how this quality was embedded into laboratory practice, will be examined. Subsequently, it will become evident that the specific image of nature produced by the stereoscopic microscope corresponded to the new ideals of the life sciences and their representation. (shrink)

Luminance and color are strong and self-sufficient cues to pictorial depth in visual scenes and images. The present study investigates the conditions Under which luminance or color either strengthens or overrides geometric depth cues. We investigated how luminance contrasts associated with color contrast interact with relative height in the visual field, partial occlusion, and interposition in determining the probability that a given figure is perceived as ‘‘nearer’’ than another. Latencies of ‘‘near’’ responses were analyzed to test for effects (...) of attentional selection. Figures in a pair were supported by luminance contrast or isoluminant color contrast and combined with one of the three geometric cues. The results of Experiment 1 show that luminance contrasts associated with hue, when it does not interact with other hues, produces the same effects as achromatic luminance contrasts: The probability of‘‘near’’ increases with luminance contrast while the latencies for ‘‘near’’ responses decrease. Partial occlusion is found to be a strong enough pictorial cue to support a weaker red luminance contrast. Interposition cues lose out against cues of spatial position and partial occlusion. The results of Experiment 2, with isoluminant displays of varying color contrast, reveal that red color contrast on a light background supported by any of the three geometric cues wins over green or white supported by any of the three geometric cues. On a dark background, red color contrast supported by the interposition cue loses out against green or white color contrast supported by partial occlusion. These findings reveal that color is not an independent depth cue, but is strongly influenced by luminance contrast and stimulus geometry. Systematically shorter response latencies for stronger ‘‘near’’ percepts demonstrate that selective visual attention reliably detects the most likely depth cue combination in a given configuration. (shrink)

It is common for visitors to have rich and varied experiences in the limited space of a classical Chinese garden. This leads to the sense that the garden’s scale is much larger than it really is. A main reason for this perceptual bias is the gardener’s manipulation of visual information. Most studies have discussed this phenomenon in terms of qualitative description with fragmented perspectives taken from static points, without considering ambient visual information or continuously changing observation points. A general question (...) arises, then, on why depth perception can vary from one observation point to another along a garden path. To better understand the spatial experience in classical Chinese gardens, this study focused on variations in perceived depth among different observation points and aimed to identify influential visual information through psychophysical experimentation. As stimuli for the experiment, panoramic photos of Liu garden were taken from three positions at Lvyin Pavilion. Considering the effects of pictorial visual cues on depth perception, the photos were processed to create 18 kinds of stimuli. Two tasks were presented to the participants. In Task 1, 71 participants were asked to rate the depth value of the garden using the magnitude estimation method in a cave automatic virtual environment. Statistical analysis of Task 1 revealed that depth values differed significantly among different viewpoints. In Task 2, participants were asked to compare 18 stimuli and 3D images presented on three connected monitors and to judge the depth of the garden using the adjustment method. The results of Task 2 again showed that depth values differed significantly among different viewpoints. In both tasks, ambient information significantly influenced depth perception. (shrink)

The Greenough stereomicroscope, or “Stemi” as it is colloquially known among microscopists, is a stereoscopic binocular instrument yielding three-dimensional depth perception when working with larger microscopic specimens. It has become ubiquitous in laboratory practice since its introduction by the unknown scientist Horatio Saltonstall Greenough in 1892. However, because it enabled new experimental practices rather than new knowledge, it has largely eluded historical and epistemological investigation, even though its design, production, and reception in the scientific community was inextricably (...) connected to the new epistemological ideals of the life sciences caught between natural history and modern science. The development of the microscope will be contextualized within the scientific and technological landscape, showing how Greenough navigated his way through this terrain, and what led him to sow the seeds for the stereoscopic microscope. The historical controversy over the optical mechanism, through which the instrument would generate the desired depth perception, and how this quality was embedded into laboratory practice, will be examined. Subsequently, it will become evident that the specific image of nature produced by the stereoscopic microscope corresponded to the new ideals of the life sciences and their representation. (shrink)

A single case study of a patient, D.M., with a lesion in the region of the right occipito-temporal gyrus is presented. D.M. had well-preserved language and general cognitive abilities. Colour discrimination, contrast sensitivity, gross depth perception, spatial localization, and motion appreciation were within normal limits.On the evaluation of perceptual abilities, he failed to identify two-dimensional shapes from stereoscopic vision, motion, and texture although in all cases he was able to identify the rough area subtended by the shape. (...) These findings are considered in relation to the current anatomical-physiological functional models of vision and it is suggested that D.M. 's deficits provide evidence for the existence in man of a functional pathway involved in the computation of texture and fine aspects of shape, which is distinct from the pathways involved in motion and stereopsis processing on one hand and colour and coarse aspects of form on the other hand. (shrink)

: This commentary focuses on the scientific status of perceptual projection-a central feature of Pereira’s projective theory of consciousness. In his target article, he draws on my own earlier work to develop an explanatory framework for integrating first-person viewable conscious experience with the third-person viewable neural correlates and antecedent causes that form conscious experience into a bipolar structure that contains both a sense of self and a sense of the world. I stress that perceptual projection is a psychological effect and (...) list many of the ways it has been studied within experimental psychology, for example in studies of depth perception in vision and audition and experiences of depth arising from cues arranged on two-dimensional surfaces in stereoscopic pictures, 3D cinemas, holograms, and virtual realities. I then juxtapose Pereira’s explanatory model with two other models that have similar aims and background assumptions but different orientations, Trehub’s Retinoid model, which focuses largely on the neural functioning of the visual system, and Rudrauf et al’s Projective Consciousness Model, which draws largely on projective geometries to specify the requirements of organisms that need to navigate a three-dimensional world, and how these might be implemented in human information processing. Together, these models illustrate both converging and diverging approaches to understanding the role of projective processes in human consciousness. Resumo: Este comentário enfoca o status científico da projeção perceptiva - uma característica central da teoria da consciência de Pereira. Em seu artigo alvo, ele recorre ao meu trabalho anterior para desenvolver uma estrutura explicativa para integrar a experiência consciente visível em primeira pessoa com os correlatos neurais visíveis de terceira pessoa e as causas antecedentes que formam a experiência consciente em uma estrutura bipolar que contém tanto um sentido de eu e um sentido do mundo. Enfatizo que a projeção perceptiva é um efeito psicológico e relaciono modalidades de seu estudo na psicologia experimental, por exemplo em estudos de percepção de profundidade em visão e audição, experiências de profundidade em superfícies bidimensionais em imagens estereoscópicas, cinemas 3D, hologramas e realidades virtuais. Eu então justaponho o modelo explicativo de Pereira com dois outros modelos que têm objetivos e suposições similares, mas orientações diferentes, o modelo do sistema retinóide de Trehub, que se concentra principalmente no funcionamento neural do sistema visual, e o modelo de consciência projetiva de Rudrauf et al., que estabelece raciocínios geométricos para especificar os requisitos de organismos que precisam navegar em um mundo tridimensional, e como eles podem ser implementados no processamento de informação no contexto humano. Juntos, esses modelos ilustram abordagens convergentes e divergentes para compreender o papel dos processos projetivos na consciência humana. (shrink)

Two experiments were performed to explore the mechanisms of human 3D shape perception. In Experiment 1, the subjects’ performance in a shape constancy task in the presence of several cues (edges, binocular disparity, shading and texture) was tested. The results show that edges and binocular disparity, but not shading or texture, are important in 3D shape perception. Experiment 2 tested the effect of several simplicity constraints, such as symmetry and planarity on subjects’ performance in a shape constancy task. (...) The 3D shapes were represented by edges or vertices only. The results show that performance with or without binocular disparity is at chance level, unless the 3D shape is symmetric and/or its faces are planar. In both experiments, there was a correlation between the subjects’ performance with and without binocular disparity. Our study suggests that simplicity constraints, not depth cues, play the primary role in both monocular and binocular 3D shape perception. These results are consistent with our computational model of 3D shape recovery. (shrink)

The concept of depth is central to Merleau-Ponty’s phenomenology and informed not only his philosophy of perception but also his thinking about psychology, art and politics. This article traces the ways the notion of depth appears in Merleau-Ponty’s thinking in these fields, contrasting it with Husserl’s own phenomenological investigations. The article starts with a comparison of the function of perception in Husserl’s phenomenology and then proceeds with an analysis of how the issue of depth reappears (...) in Merleau-Ponty’s phenomenology of perception, phenomenology of art and political philosophy. I argue that while Husserl’s approach to phenomenology led him to analyses of aesthetics stemming from works of art as random examples, and to non-participation in politics, Merleau-Ponty’s phenomenology leads to the opposite approach, inviting concrete criticism in art and active participation in politics. It is argued that Merleau-Ponty’s approach is more philosophically consistent. The choice of particular works of art, and the particular political engagements, can retrospectively clarify the transcendental phenomenological investigations themselves. (shrink)

Little is known about distance processing in patients with posterior brain damage. Although many investigators have claimed that distance estimates are normal or abnormal in some of these patients, many of these observations were made informally and the examiners often asked for relative, and not absolute, distance estimates. The present investigation served two purposes. First, we wanted to contrast the use of distance information in peripersonal space for perceptual report as opposed to visuomotor control in our visual form agnosic patient, (...) DF. Second, we wanted to see to what extent her abilities to process distance cues were dependent on binocular vision, in light of Milner et al.'s (1991) observations of preserved stereopsis in DF, and Dijkerman et al.'s (1996) and Marotta et al.'s (1997) observations that her visual guidance of grasping may be particularly dependent on binocular vision of the target. We hypothesized that DF's visuomotor responses would show normal sensitivity to target distance, while her perceptual estimates would not. In the first experiment, we required DF and two age- and sex-matched control subjects to reach out and grasp black cubes placed at varying distances, or to estimate the distance of the cubes from the hand starting position without making a reaching movement. In the second experiment, we required DF and two age-matched control subjects to point as rapidly and accurately as possible to small LED targets which differed in spatial location, under binocular and monocular conditions. The results showed that, relative to the control subjects, DF's grasping movements produced normal peak velocity-distance scaling-when she reached for blocks which varied in depth or pointed to LED targets which were presented at different distances in depth. In contrast, in the cube experiment, her verbal estimates of object distance were poorly scaled, although they improved slightly under the binocular conditions. The results are discussed in terms of current theories of processing streams in extrastriate visual cortex and the distinction between categorical and coordinate spatial processing. (shrink)

Very encouraging results have been obtained from a new program that derives a dense three-dimensional evidence grid representation of a robot's surroundings from wide-angle stereoscopic images. The pro gram adds several spatial rays of evidence to a grid for each of about 2,500 local image features chosen per stereo pair. It was used to construct a 256x256x64 grid, representing 6 by 6 by 2 meters, from a hand- collected test set of twenty stereo image pairs of an office scene. (...) Fifty nine stereo pairs of an 8 by 8 meter laboratory were also processed. The positive (probably occupied) cells of the grids, viewed in perspec tive, resemble dollhouse scenes. Details as small as the curvature of chair armrests are discernible. The processing time, on a 100 MIPS Sparc 20, is less than five seconds per stereo pair, and total memory is under 16 megabytes. The results seem abundantly adequate for very reliable navigation of freely roaming mobile robots, and plausibly adequate for shape identification of objects bigger than 10 centimeters. The program is a first proof of concept, and awaits optimizations, enhancements, variations, extensions and applications. (shrink)