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At least 91 records · Page 5Linked to original sources
PubMed2005

A reversed structure-from-motion effect for simultaneously viewed stereo-surfaces.

A spatially flat stimulus is perceived as varying in depth if its velocity structure is consistent with that of a three-dimensional (3D) object. This is structure from motion (SFM). We asked if the converse effect also exists. A motion-from-structure effect would skew an object's perceived velocity structure to make it more consistent with the 3D structure provided by its depth cues. This proposed phenomenon should be opposite in sign from velocity constancy and could potentially interfere with it. Previous tests of velocity constancy compared stimuli presented at different times, not simultaneously. This explains why a reversal of SFM has not been previously reported, as it is expected to appear only for simultaneous presentations. We tested this prediction using random-dot stereograms to define two adjacent moving surfaces separated in stereoscopic depth. We found that subjects did not perceive velocity constancy with either simultaneous or sequential stimulus presentations. For sequential presentations, subjects matched retinal speeds, in agreement with previous work. However, for simultaneous presentations, the nearer surface was seen as moving faster when both surfaces were moving with the same retinal speed, an effect opposite in polarity from velocity constancy and a signature of the motion-from-structure phenomenon.

Calibration↗
PubMed2005

Exogenous attention and endogenous attention influence initial dominance in binocular rivalry.

We investigated the influence of exogenous and endogenous attention on initial selection in binocular rivalry. Experiment 1 used superimposed +/-45 degrees gratings viewed dioptically for 3s, followed by a brief contrast increment in one of the gratings to direct exogenous attention to that grating. After a brief blank period, dichoptic stimuli were presented for various durations (100-700 ms). Exogenous attention strongly influenced which stimulus was initially dominant in binocular rivalry, replicating an earlier report (Mitchell, Stoner, & Reynolds. (2004). Object-based attention determines dominance in binocular rivalry. Nature, 429, 410-413). In Experiment 2, endogenous attention was manipulated by having participants track one of two oblique gratings both of which independently and continuously changed their orientations and spatial frequencies during a 5s period. The initially dominant grating was most often the one whose orientation matched the grating correctly tracked using endogenous attention. In Experiment 3, we measured the strength of both exogenous and endogenous attention by varying the contrast of one of two rival gratings when attention was previously directed to that grating. The contrast of the attended grating had to be reduced by an amount in the neighborhood of 0.3 log-units, to counteract attention's boost to initial dominance. Evidently both exogenous and endogenous attention can influence initial dominance of binocular rivalry, effectively boosting the stimulus strength of the attended rival stimulus.

Adaptation, Ocular↗
PubMed2006

Effects of depth, eccentricity and size of additional static stimulus on visually induced self-motion perception.

Static visual stimulus presented behind a moving pattern inhibits vection. On the other hand, the same static stimulus facilitates vection if it is located in front of the moving pattern. In this study, the effects of depth, eccentricity and size of the additional static stimulus on inhibition and facilitation of horizontal linear vection were investigated. Results indicated that both inhibition and facilitation become conspicuous with increasing the size of the static stimulus. Furthermore, the inhibition caused by the static foreground is dominated by the central stimulus, while the facilitation caused by the static background is more effective in the peripheral stimulus.

Depth Perception↗
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↗
PubMed2006

Amodal completion with background determines depth from monocular gap stereopsis.

Grove, Gillam, and Ono [Grove, P. M., Gillam, B. J., & Ono, H. (2002). Content and context of monocular regions determine perceived depth in random dot, unpaired background and phantom stereograms. Vision Research, 42, 1859-1870] reported that perceived depth in monocular gap stereograms [Gillam, B. J., Blackburn, S., & Nakayama, K. (1999). Stereopsis based on monocular gaps: Metrical encoding of depth and slant without matching contours. Vision Research, 39, 493-502] was attenuated when the color/texture in the monocular gap did not match the background. It appears that continuation of the gap with the background constitutes an important component of the stimulus conditions that allow a monocular gap in an otherwise binocular surface to be responded to as a depth step. In this report we tested this view using the conventional monocular gap stimulus of two identical grey rectangles separated by a gap in one eye but abutting to form a solid grey rectangle in the other. We compared depth seen at the gap for this stimulus with stimuli that were identical except for two additional small black squares placed at the ends of the gap. If the squares were placed stereoscopically behind the rectangle/gap configuration (appearing on the background) they interfered with the perceived depth at the gap. However when they were placed in front of the configuration this attenuation disappeared. The gap and the background were able under these conditions to complete amodally.

Color Perception↗
PubMed2006

The pursuit theory of motion parallax.

Although motion parallax is closely associated with observer head movement, the underlying neural mechanism appears to rely on a pursuit-like eye movement signal to disambiguate perceived depth sign from the ambiguous retinal motion information [Naji, J. J., & Freeman, T. C. A. (2004). Perceiving depth order during pursuit eye movement. Vision Research, 44, 3025-3034; Nawrot, M. (2003). Eye movements provide the extra-retinal signal required for the perception of depth from motion parallax. Vision Research, 43, 1553-1562]. Here, we outline the evidence for a pursuit signal in motion parallax and propose a simple neural network model for how the pursuit theory of motion parallax might function within the visual system. The first experiment demonstrates the crucial role that an extra-retinal pursuit signal plays in the unambiguous perception of depth from motion parallax. The second experiment demonstrates that identical head movements can generate opposite depth percepts, and even ambiguous percepts, when the pursuit signal is altered. The pursuit theory of motion parallax provides a parsimonious explanation for all of these observations.

Computer Peripherals↗
PubMed2006

Interocular interactions during acuity measurement in children and adults, and in adults with amblyopia.

The binocular interactions that occur during dichoptic and binocular viewing were investigated using a letter acuity task in normally sighted children (age range 6-14 years) and adults, and in adults with anisometropic amblyopia. Our aims were to investigate the nature of binocular interactions that occur in each group, and the extent to which the characteristics of binocular interactions differ across the groups. The non-tested eye was occluded during monocular (baseline) viewing, and was allowed to view a uniform stimulus with fusion lock in dichoptic viewing. In adults and children with normal vision, acuity under dichoptic viewing was unchanged relative to monocular baseline in the dominant eyes, while acuity of the non-dominant eye improved under dichoptic viewing relative to baseline. The magnitude of dichoptic change in the non-dominant eyes was similar in the two normally sighted groups, but the dichoptic advantage was found to decrease with increasing age within the children tested. Binocular acuity was better than monocular acuity in normal subjects, and a decrease in binocular summation with age was noted within the age range of the children tested. In contrast, the amblyopic observers showed no change in acuity with viewing conditions. The results demonstrate development of interocular interactions during childhood, and wide inter-individual variation in pattern of interocular interactions among anisometropic amblyopic adults.

Adolescent↗
PubMed2006

Stimulus flicker alters interocular grouping during binocular rivalry.

When the two eyes are presented with sufficiently different stimuli, the stimuli will engage in binocular rivalry. During binocular rivalry, a subject's perceptual state alternates between awareness of the stimulus presented to the right eye and that presented to the left eye. There are instances in which competition is not eye-based, but instead takes place between stimulus features, as is the case in flicker and switch rivalry (F&S). Here we investigate another such instance, interocular grouping, using a Diaz-Caneja type stimulus in conjunction with synchronous stimulus flicker. Our results indicate that stimulus flicker increases the total duration of interocularly bound percepts, and that this effect occurs for a range of temporal flicker frequencies. Furthermore, the use of contrast-inversion flicker causes a decrease of total dominance duration of the interocularly bound percepts. We argue that different flickering regimes can be used to differentially stimulate lower and higher levels of visual processing involved in binocular rivalry. We propose that the amount of interocularly combined pattern-completed percept can be regarded as a measure of the level at which binocular rivalry is resolved.

Dominance, Ocular↗
PubMed2006

Peripheral fading with monocular and binocular viewing.

This study measured the fading times of peripheral targets as a function of whether viewing was monocular or binocular, and of brightness contrast. Data from a binocularly normal group showed Troxler fading to be significantly faster with monocular (i.e., patched) than with binocular viewing. In contrast, one-eyed observers showed significantly longer fading times than the two-eyed observers viewing monocularly and equivalent times to their binocular viewing. A control experiment showed that these findings were not due to worse fixation stability, larger pupil sizes, or an unusually large blinking rate in the enucleated group. The enucleated group actually exhibited a slight miosis, equivalent fixation stability, and a normal blinking rate. In both experiments, the times to fading of all observers were a function of brightness contrast. We conclude that in binocularly normal observers patching or closing one eye does not produce monocular vision but rather a condition of weak binocular rivalry, and that the absence of inhibitory binocular interactions in the enucleated group may explain, in part, their resistance to fading and their superior performance in other contrast-defined tasks.

Adolescent↗
PubMed2006

Temporal frequency and contrast tagging bias the type of competition in interocular switch rivalry.

The nature of competition underlying perceptual alternations in binocular rivalry remains controversial. Interocular swapping of rivalrous stimuli can result in either slow irregular perceptual alternations that bridge multiple interocular switches or fast regular alternations that are time locked to the stimulus exchanges. We labeled either the inputs to the eyes or the individual rivalrous stimuli using temporal frequency and contrast tagging. Tagging of eye-of-origin signals enhanced the fast regular perceptual alternations associated with eye rivalry, while stimulus tagging shifted perception towards slow irregular alternations characteristic of stimulus rivalry. Thus, the type of competition in binocular rivalry can be biased based on additional cues in the visual inputs. The results are consistent with a model in which the brain combines information across multiple visual features to resolve ambiguities in visual inputs.

Contrast Sensitivity↗
PubMed2000

Binocular cues are important in controlling the grasp but not the reach in natural prehension movements.

Binocular cues are typically considered to be pre-eminent in the control of reaching and grasping behaviour. However, in the absence of such information prehension movements can still be accurate and reliable. The present study therefore was designed to assess further the contribution of binocular information in the control of human reaching and grasping movements. Participants reached for and picked up objects under binocular and monocular viewing, both in the absence of a visible scene around the target objects (complete darkness with 'self-illuminated' objects and hand), and under normal (fully illuminated) viewing. Analysis of kinematic parameters indicated that the removal of binocular information did not significantly affect the major indices of the transport component, although it did affect the grasp component. In contrast, the kinematic parameters in the unlit conditions revealed that both the transport component and the grasp component of the reach were severely disrupted whether binocular cues were available or not. Our results suggest that binocular information may be more important for the control of grasp formation than for the control of the transport component. Elimination of the surrounding scene and normal visual feedback affects both the transport and the grasp. It is concluded that in normal viewing conditions, reaching and grasping movements are less dependent on binocular information than has previously been thought.

Adult↗
PubMed1999

Motion parallax enables depth processing for action in a visual form agnosic when binocular vision is unavailable.

Visual-form agnosic patient DF, who has severe difficulties in using visual information about size, shape and orientation for perceptual report, can nevertheless--under normal viewing conditions--use the same information to accurately guide her hand movements. However, her performance of prehension tasks requiring the analysis of visual depth is severely disrupted when binocular vision is prevented. We have suggested that this deterioration in visuomotor control is due to an inability to use pictorial depth cues to compensate for the removal of binocular vision. In the current study we investigated whether DF was able to use motion parallax as an alternative to binocular cues. We asked her to grasp a square plaque slanted at different orientations in depth, under two monocular testing conditions. In one condition her head remained stationary on a chin rest, and in the other condition she made large lateral head movements just prior to each prehension movement. The results confirmed that DF is impaired in adjusting her hand orientation to the orientation of the target object when reaching monocularly with her head stationary. In contrast, when she made head movements, her manual performance was restored to almost normal levels. Our results are consistent with the idea that the processing of pictorial depth cues depends on the cortical ventral stream, which is known to be disrupted by DF's lesion. They further indicate that orientation in depth can be computed from motion parallax just as well as from binocular cues in the absence of a normally functioning ventral stream.

Adult↗
PubMed2000

Monocular lustre from flicker.

A spot that flickers at 16 Hz between two luminance levels (on a grey surround) has an appearance of metallic lustre, which we call 'monocular lustre'. Binocular and monocular lustre were measured in comparable conditions by a rating procedure, and both were reported only when the light and dark values of the flickering (or binocularly fused) spot straddled the surround luminance, so that the spot was alternately brighter and darker than the surround. We attribute lustre to competition between ON and OFF visual pathways.

Flicker Fusion↗
PubMed2001

Phantom surface captures stereopsis.

A phantom surface is a stereoscopic illusory area that can be seen in depth although there is no conventional stereoscopic cues [Liu, L., Stevenson, S.B., & Schor, C.M. (1994). Quantitative stereoscopic depth without binocular correspondence. Nature, 367, 66-69; Gillam, B. & Nakayama, K. (1999). Quantitative depth for a phantom surface can be based on cyclopean occlusion cues alone. Vision Research, 39, 109-112]. The phenomenon has been explained as an example of half-occlusion processing in which the visual system uses information about cyclopean occlusion structure of the visual world. We created stereo capture stereograms in which phantom surfaces changed the perceived depth of conventionally defined binocular textures. Because conventional stereoscopic matching is strongly affected by half-occlusion processing, we suggest that half-occlusion processing is an integral part of the early stereoscopic processing and solving of the correspondence problem.

Depth Perception↗
PubMed2001

Filling-in at the natural blind spot contributes to binocular rivalry.

The human natural blind spot is usually filled in based on the contextual information. When two sufficiently different images are presented to the two eyes, observers typically perceive an alternation between the two images (binocular rivalry). Both the filling-in process and binocular rivalry have been the subject of considerable research. This study investigates whether filled information in one eye's natural blind spot can contribute to binocular rivalry. A radial grating (D=12 degrees ) was presented to one eye, centered on the natural blind spot. Observers perceived a complete figure in monocular view; the blind spot area was filled-in based on the surrounding information. Simultaneously, a circular grating smaller than the blind spot (D=4 degrees ), was presented to the fellow eye in the region corresponding to the other eye's blind spot. The amount of rivalry as indexed by how often the smaller circular grating remained visible was measured. The results suggest that the filled information in the area of the blind spot does contribute to the rivalry process.

Humans↗
PubMed2001

Motion rivalry impairs motion repulsion.

In their classic study on motion repulsion, Marshak and Sekuler (Science 205 (1979) 1399) reported a repulsion of up to 10 degrees when two different directions of motion were presented dichoptically. However, subjects in that study did not experience binocular rivalry, presumably because of the brief presentation time. In the present study, we measured repulsion during binocular rivalry by requiring subjects to dichoptically view the stimuli until one direction of motion appeared to exclusively dominate the other (Blake, Yu, Lokey, & Norman (1998). J. Cogn. Neurosci., 10, 46-60). We found that motion repulsion was significantly reduced during exclusive dominance. Indeed, after controlling for reference repulsion--the misjudgment of a single direction of motion (Rauber & Treue (1998). Perception, 27, 393-402)--we found no significant motion repulsion during exclusive dominance. These data suggest that motion repulsion may require the perception, rather than merely the physical presence, of multiple directions.

Humans↗
PubMed2002

The role of the cyclopean eye in vision: sometimes inappropriate, always irrelevant.

During binocular fixation, the eyes usually point in different directions, and yet, each object is judged to lie in a single direction. It is commonly believed that a particular location in the head serves as the origin for such directional judgments. This location is known as the cyclopean eye. We argue here that observers can judge visually perceived directions from angular information alone, and do not require positional information supplied by a cyclopean eye. We show that experimental findings reported as evidence for the cyclopean concept can also be explained solely by angular information without the need for a cyclopean eye. Recent findings concerning binocular shape perception and the cyclopean illusion demonstrate that binocular perception is incompatible with vision from a single vantage point. The concept of the cyclopean eye is sometimes inappropriate and always irrelevant as far as vision is concerned.

Depth Perception↗
PubMed2002

Luminance spatial scale and local stereo-sensitivity.

Using filtered, broad band, fractal noise images we measured the dependence of D(min) and D(max) for stereo on luminance spatial frequency. D(min) was found to exhibit a simple dependence on the highest spatial frequency contained in the stimulus. D(max) depended on both image size and spatial frequency in a way that suggests an informational limit. Different rules govern D(min) and D(max) even for first order stereopsis, arguing against a common neural explanation based on independent access to the most pertinent spatial filter.

Depth Perception↗