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PubMed1996

Stereoscopic depth constancy depends on the subject's task.

Under identical viewing conditions, observers made two types of judgement about the shape of stereoscopically defined surfaces: one required an estimate of viewing distance for correct performance (e.g. setting the depth of a hemi-cylinder to equal its half-height or a dihedral angle to 90 deg), the other did not (matching the depth of, for example, sinusoidal corrugations or hemi-cylinders presented at two distances). Depth constancy for the two types of task was about 75% and 100%, respectively. We argue that observers may use a simple "direct" strategy to perform the depth matching task rather than constructing and comparing a metric representation of each surface.

Convergence, Ocular↗
PubMedDate not supplied

Influence of the gravitational vertical on geometric visual illusions.

The occurrence of geometric orientation illusions and the perception of ambiguous figures were analyzed in 24 subjects during static body tilt relative to gravity on Earth. Results showed that illusions such as the Rock's diamond/square, the Ponzo illusion, and orientation contrast illusions occurred less frequently, and that depth reversal of ambiguous figures took more time when subjects were lying on their side or supine compared to upright, thus suggesting that the gravitational reference plays a significant role in these "visual" illusions. The structure of images, our representation of the environment, and orientation relative to gravity are all integral parts in interpreting visual images. In a weightless environment where no gravitational reference can be used, it is expected that similar alterations in visual perception will occur.

Adult↗
PubMed2003

When does grouping happen?

Recent research on perceptual grouping is described with particular emphasis on identifying the level(s) at which grouping factors operate. Contrary to the classical view of grouping as an early, two-dimensional, image-based process, recent experimental results show that it is strongly influenced by phenomena related to perceptual constancy, such as binocular depth perception, lightness constancy, amodal completion, and illusory contours. These findings imply that at least some grouping processes operate at the level of phenomenal perception rather than at the level of the retinal image. Preliminary evidence is reported showing that grouping can affect perceptual constancy, suggesting that grouping processes must also operate at an early, preconstancy level. If so, grouping may be a ubiquitous, ongoing aspect of visual organization that occurs for each level of representation rather than as a single stage that can be definitively localized relative to other perceptual processes.

Depth Perception↗
PubMed2005

Response monitoring and expectancy in random serial RT tasks.

Two different sequential patterns have been reported in serial reaction-time (RT) tasks with random stimulus sequences, depending on the response-to-stimulus interval (RSI). When RSI is short a first-order repetition effect and a higher order benefit-only pattern are found, and when RSI is long a cost-benefit pattern is observed. In a series of three experiments, we found that the patterns are not unique for spatial dimensions, and that the benefit-only pattern does not appear for irrelevant stimulus features. The cost-benefit pattern, on the other hand, can shift to irrelevant locations, but not to irrelevant colour. Distributional analyses of the sequential effects demonstrate that the first-order repetition effect can be dissociated from the higher order effects. The results are interpreted as support for the role of response monitoring in the development of the benefit-only pattern at short RSI, while the first-order repetition effect is explained as repetition priming. With a long RSI, the cost-benefit pattern is confirmed as a low-level subjective expectancy process, which is primarily controlled by stimulus location. The data clearly strengthen the support for three different processes generating sequential effects in random serial RT tasks.

Adult↗
PubMed2006

Surface geometry influences the shape of illusory contours.

Geometric and neural models of illusory-contour (IC) synthesis currently use only local contour geometry to derive the shape of ICs. Work on the visual representation of shape, by contrast, points to the importance of both contour and surface geometry. We investigated the influence of surface-based geometric factors on IC shape. The local geometry of inducing-contour pairs was equated in stereoscopic IC displays, and the shape of the enclosed surface was varied by manipulating sign of curvature, cross-axial shape width, and medial-axis geometry. IC shapes were measured using a parametric shape-adjustment task (Experiment 1) and a dot-adjustment task (Experiment 2). Both methods revealed large influences of surface geometry. ICs enclosing locally concave regions were perceived to be systematically more angular than those enclosing locally convex regions. Importantly, the influence of sign of curvature was modulated significantly by shape width and medial-axis geometry: IC shape difference between convex and concave inducers was greater for narrow shapes than wider ones, and greater for shapes with straight axis and symmetric contours (diamond versus bowtie), than those with curved axis and parallel contours (bent tubes). Even at the level of illusory "contours," there is a contribution of region-based geometry which is sensitive to nonlocal shape properties involving medial geometry and part decomposition. Models of IC synthesis must incorporate the role of nonlocal region-based geometric factors in a way that parallels their role in organizing visual shape representation more generally.

Depth Perception↗
PubMed2006

The increased accumulation of structurally modified versican and decorin is related with the progression of laryngeal cancer.

Versican and decorin, two proteoglycans (PGs) with contradictory roles in the pathophysiology of cancer, comprise important stromal components in many tumor types and play a crucial role in the progression of cancer. In this study, we provide direct evidence for a significant and stage-related accumulation of versican and decorin in the tumor-associated stroma of laryngeal squamous cell carcinoma (LSCC) in comparison to normal larynx. Both PGs were found to be co-localized within the peritumorous stroma. In addition, the accumulated versican and decorin were markedly modified on both protein core and glycosaminoglycan (GAG) levels. Decorin, which was present under both glycanated and non-glycanated forms, perceptibly increased with the progression of LSCC, compared to the normal larynx. Tumor-associated glycanated decorin was found to contain significant amounts of dermatan sulfate (DS) sequences. Versican was also found to undergo stage-related structural modifications since a marked heterogeneity of protein cores was observed, being intense in late stage of laryngeal cancer. The increased accumulation of both versican and decorin was associated with a significant stage-related increase of the molar ratio of Delta di-mono4S to Delta di-mono6S up to approximately threefold in LSCC compared to the normal ones. The modified chemical structure of both PGs could be associated with the degree of aggressiveness of laryngeal squamous cell carcinomas.

Carcinoma, Squamous Cell↗
PubMed2005

The ties that keep us bound: Top-down influences on the persistence of shape-from-motion.

The phenomenon of perceptual persistence after the motion stops in shape-from-motion displays (SFM) was used to study the influence of prior knowledge on the maintenance of a percept in awareness. In SFM displays an object composed of discontinuous line segments are embedded in a background of randomly oriented lines. The object only becomes perceptible when the line segments that compose the object and the lines that compose the background move in counterphase. Critically, once the movement of the line segments stops, the percept of the object persists for a short period of time. In the present study, perceptual persistence for digits exceeded that reported for nonsense shapes composed of the same line segments. This result is taken as evidence that the processes involved in the persistence of SFM, and therefore sustained perception, are sensitive to top-down influences.

Adult↗
PubMed2006

The impact of object size and rigidity on infant reaching.

Although the changes in kinematics of infant reaching have been studied, few researchers have investigated the improvement of reaching regarding objects of distinct physical properties. The aim of this longitudinal study was to verify the impact of object size and rigidity on the development of reaching in 4-6-month-old infants. Four infants were observed with a motion capture system during trials with four objects of distinct sizes and rigidity. A total of 188 reaches were analyzed by using the 3D movement reconstruction. Our results showed that reaching frequency, mean velocity, and straightness index increased with age. The number of movement units decreased with age and increased for small objects. Rigidity was not shown to affect reaching trajectories. These findings suggest that infants are capable of perceiving the more relevant object properties, thus using their available motor capabilities to modify the essential variables so that they can reach the target more accurately.

Distance Perception↗
PubMed2005

Cross-modal activation of visual cortex during depth perception using auditory substitution of vision.

Previous neuroimaging studies identified multimodal brain areas in the visual cortex that are specialized for processing specific information, such as visual-haptic object recognition. Here, we test whether visual brain areas are involved in depth perception when auditory substitution of vision is used. Nine sighted volunteers were trained blindfolded to use a prosthesis substituting vision with audition both to recognize two-dimensional figures and to estimate distance of an object in a real three-dimensional environment. Using positron emission tomography, regional cerebral blood flow was assessed while the prosthesis was used to explore virtual 3D images; subjects focused either on 2D features (target search) or on depth (target distance comparison). Activation foci were found in visual association areas during both the target search task, which recruited the occipito-parietal cortex, and the depth perception task, which recruited occipito-parietal and occipito-temporal areas. This indicates that some brain areas of the visual cortex are relatively multimodal and may be recruited for depth processing via a sense other than vision.

Acoustic Stimulation↗
PubMed2005

A novel method for assessing contrast sensitivity in the beagle dog is sensitive to age and an antioxidant enriched food.

Tasks requiring visual discrimination are commonly used in assessment of canine cognitive function. However, little is known about canine visual processing, and virtually nothing is known about the effects of age on canine visual function. This study describes a novel behavioural method developed to assess one aspect of canine visual function, namely contrast sensitivity. Four age groups (young, middle aged, old, and senior) were studied. We also included a group of middle aged to old animals that had been maintained for at least 4 years on a specially formulated food containing a broad spectrum of antioxidants and mitochondrial cofactors. Performance of this group was compared with a group in the same age range maintained on a control diet. In the first phase, all animals were trained to discriminate between two high contrast shapes. In the second phase, contrast was progressively reduced by increasing the luminance of the shapes. Performance decreased as a function of age, but the differences did not achieve statistical significance, possibly because of a small sample size in the young group. All age groups were able to acquire the initial discrimination, although the two older age groups showed slower learning. Errors increased with decreasing contrast with the maximal number of errors for the 1% contrast shape. Also, all animals on the antioxidant diet learned the task and had significantly fewer errors at the high contrast compared with the animals on the control diet. The initial results suggest that contrast sensitivity deteriorates with age in the canine while form perception is largely unaffected by age.

Aging↗
PubMed2004

Asymmetry in the perception of motion-in-depth.

We investigated the anisotropic responses between the detection of motion toward and motion away from the observers with expanding/contracting shaded circles. Our experiments followed visual search paradigm with two exceptions: (1) the stimulus presentation time was fixed for 300 ms and (2) the mean error rates were adopted as a dependent variable. In Experiment 1, targets and distractors were defined by expanding (or contracting) convex/concave circles. Results of Experiment 1 suggested that the human visual system is more sensitive to expanding convex circles (which create the impression of approaching objects) than others. In Experiment 2, the targets and distractors were defined by expanding (or contracting) step gradient (top-lighting/bottom-lighting) circles. The results of Experiment 2 suggest that the anisotropy for the perception of motion-in-depth should not be caused by change of luminance polarity but by change of shading cue.

Adolescent↗
PubMed2004

No evidence for sequential effects of the interaction of stereo and motion cues in judgements of perceived shape.

The interaction of the depth cues of binocular disparity and motion parallax could potentially be used by the visual system to recover an estimate of the viewing distance. The present study investigated whether an interaction of stereo and motion has effects that persist over time to influence the perception of shape from stereo when the motion information is removed. Static stereoscopic ellipsoids were presented following the presentation of rotating stereoscopic ellipsoids, which were located either at the same or a different viewing distance. It was predicted that shape judgements for static stimuli would be better after presentation of a rotating stimulus at the same viewing distance, than after presentation of one at a different viewing distance. No such difference was found. It was concluded that an interaction between stereo and motion depth cues does not influence the perception of subsequently presented static objects.

Cues↗
PubMed2004

A laminar cortical model for 3D perception of slanted and curved surfaces and of 2D images: development, attention, and bistability.

A model of laminar visual cortical dynamics proposes how 3D boundary and surface representations arise from viewing slanted and curved 3D objects and 2D images. The 3D boundary representations emerge from non-classical receptive field interactions within intracortical and intercortical feedback circuits. Such non-classical interactions within cortical areas V1 and V2 contextually disambiguate classical receptive field responses to ambiguous visual cues using cells that are sensitive to colinear contours, angles, and disparity gradients. Remarkably, these cell types can all be explained as variants of a unified perceptual grouping circuit whose most familiar example is a 2D colinear bipole cell. Model simulations show how this circuit can develop cell selectivity to colinear contours and angles, how slanted surfaces can activate 3D boundary representations that are sensitive to angles and disparity gradients, how 3D filling-in occurs across slanted surfaces, how a 2D Necker cube image can be represented in 3D, and how bistable 3D Necker cube percepts occur. The model also explains data about slant aftereffects and 3D neon color spreading. It shows how chemical transmitters that habituate, or depress, in an activity-dependent way can help to control development and also to trigger bistable 3D percepts and slant aftereffects. Attention can influence which of these percepts is perceived by propagating selectively along object boundaries.

Attention↗
PubMed2004

Illusory contours and surfaces without amodal completion and depth stratification.

Cognitive and figural cues were studied in modified Ehrenstein figures made from letters of the alphabet instead of radial lines. Capital letters with and without terminators (L, J vs O, D) were used, oriented towards or away from the central gap. Three groups, of 14 subjects each, estimated the magnitude of either (i) the illusory contour, (ii) brightness enhancement, or (iii) apparent depth. Strong illusory contour formation and brightness enhancement, but no depth stratification, were perceived in figures devoid of apparent occlusion and amodal completion. These results demonstrate that the Ehrenstein illusion can arise from line ends--with no need for perceptual completion, showing that illusory boundaries and surfaces can be dissociated from apparent depth. Results support a bottom-up explanation in terms of end-stopped neurons in the visual cortex. Conversely, top-down processes appear to be responsible for depth stratification.

Cognition↗
PubMed2004

Effect of background motion on the perceived shape of a 3-D object.

The effect of the speed of a background surface on the judged shape of a moving object was investigated in four experiments. Observers judged the magnitude of a concave dihedral angle translating or rotating against a planar background. Judged angle magnitude decreased (indicating an increase in perceived depth) with increasing background speed until the background speed reached the speed of the front edge of the angle. Judged angle magnitude then increased with background speed until the difference between the background and front edge speed was large. A model that was previously proposed to account for angle magnitude judgments from translations and rotations is extended to displays with a moving background.

Depth Perception↗
PubMed2005

Binocular depth perception from unpaired image points need not depend on scene organization.

Dichoptic stimuli containing unmatched features can produce depth perception despite the absence of binocular disparity, a phenomenon known as da Vinci stereopsis. Unmatched points can arise from depth discontinuities and partial occlusion in the real world. It has been hypothesized that spatial organization of unmatched image features as dictated by the ecological optics of occlusion might determine perceived depth in da Vinci stereopsis. We tested this hypothesis by creating dichoptic stimuli containing unmatched points in which local cues and overall organization could be dissociated. For these stimuli, observers' perception of depth did not depend on the organization of the scene, but only on the local cues. This finding shows the perceived depth of unpaired points need not depend on reconstructing the spatial organization of depth discontinuities in real-world scenes.

Depth Perception↗
PubMed2005

Two sources of error in pop-out localization.

An odd-one-out stimulus, such as a vertical bar among horizontals, pops out from the background and is easily detected, but its location may be slightly ambiguous. Four observers were asked to pinpoint these stimuli on thousands of trials, in 5 x 5 and 9 x 9 arrays of Gabor patches. We found they made frequent errors toward neighbors of the target. Over a range of performance from 41% to 96% correct, the frequency of neighbor errors was well described by a linear function of the total error frequency, a function that might result from mixing together two spatial distributions--one broad, the other narrow. We suggest that these represent two sources of error in pop-out localization; one might correspond to a higher visual area with imprecise retinotopic mapping, and the other to a more fine-grained localization process in primary visual cortex.

Depth Perception↗