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PubMed1979

Infant perception of the invariant shape of objects varying in slant.

In a previous study employing habituation-recovery techniques, partial confirmation for shape constancy in 12-week-old infants was found. The infants may have been responding to changes in slant or slant-related cues, leaving unresolved the question of whether shape perception should be considered proximal (retinal) or distal (objective). In the present experiment 12-week-old infants were desensitized to changes in slant prior to test. Following habituation to a shape exposed at varying slants, magnitude of recovery was overwhelmingly greater for a different shape than for the same shape, indicating that the constant real shape of the habituated figure had been perceived across rotational transformations.

Depth Perception↗
PubMed2004

Perceived contrast explains asymmetries in visual-search tasks with shaded stimuli.

Shaded stimuli have traditionally been used in the context of three-dimensional (3-D) shape perception. Many studies have shown a persistent asymmetry in that a circle filled with a shaded gradient that is dark at the top and bright at the bottom (top-dark circle) is much easier to locate among top-bright circles than in the opposite arrangement (a top-bright circle among top-dark circles). The immediate 3-D interpretation of top-dark and top-bright circles as hollows and protuberances, respectively, and the asymmetry just described have been explained in terms of 3-D percepts. The work described here challenges this view: the results of the first experiment show that top-dark circles are perceived as having 10% higher contrast than top-bright circles of the same physical contrast. Experiment 2 replicates classical visual-search experiments but adding a new condition where target and distractors were subjectively equated in contrast. For five of six subjects, the ubiquitous asymmetry disappears in this condition.

Adult↗
PubMed2004

Path perception during rotation: influence of instructions, depth range, and dot density.

How do observers perceive their direction of self-motion when traveling on a straight path while their eyes are rotating? Our previous findings suggest that information from retinal flow and extra-retinal information about eye movements are each sufficient to solve this problem for both perception and active control of self-motion [Vision Res. 40 (2000) 3873; Psych. Sci. 13 (2002) 485]. In this paper, using displays depicting translation with simulated eye rotation, we investigated how task variables such as instructions, depth range, and dot density influenced the visual system's reliance on retinal vs. extra-retinal information for path perception during rotation. We found that path errors were small when observers expected to travel on a straight path or with neutral instructions, but errors increased markedly when observers expected to travel on a curved path. Increasing depth range or dot density did not improve path judgments. We conclude that the expectation of the shape of an upcoming path can influence the interpretation of the ambiguous retinal flow. A large depth range and dense motion parallax are not essential for accurate path perception during rotation, but reference objects and a large field of view appear to improve path judgments.

Awareness↗
PubMed1993

Transparent surfaces defined by implicit X junctions.

An X junction is known to be a strong cue for transparency whereas a T junction typically indicates occlusion by an opaque surface. In this article, however, we will demonstrate two cases in which special T junctions (implicit X) can support the perception of a transparent surface. The T junction is perceived as having an additional illusory contour rendering it as an implicit X junction. There is physically realizable condition in which transparency can produce a T junction and the existence of this special case may explain why T junctions are not necessarily taken as cues for opaque surface. The similar processing for X junctions and implicit Xs to form transparent surfaces is suggested.

Adult↗
PubMed1978

Effect of perspective and slant on perception of apparent size and distance.

An experiement was performed to re-examine the role of linear perspective and floor slant on apparent size and distance scales. Misleading perspective cues did not alter the observers' apparent distance scales but did influence the absolute magnitude of distance judgments; floor slant exerted little influence on apparent distance scales or the absolute magnitude of distance judgments. Neither perspective nor slant manipulation reliably affected apparent size scales or exerted more than a minor influence on the absolute magnitude of size judgments.

Cues↗
PubMed1990

Visual perception and the guidance of locomotion without vision to previously seen targets.

Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and averaged about 8% of the target distance. Unlike Thomson's (1983) findings, there was not an abrupt increase in variable error at around 9 m, and no significant time-based effects were observed. The results demonstrate the accuracy of people's visual perception of absolute egocentric distances out to 24 m under open field conditions. The accuracy of people's walking without vision to previously seen targets shows that efferent and proprioceptive information about locomotion is closely calibrated to visually perceived distance. Sensitivity to the correlation of optical flow with efferent/proprioceptive information while walking with vision may provide the basis for this calibration when walking without vision.

Adult↗
PubMed2003

[Clinical analysis of binocular anisei konia after laser in situ keratomileusis on myopic patients].

PURPOSE: To explore the effect produced by laser in situ keratomileusis (LASIK) on binocular aniseikonia(BA) and steropsis of myopic patients. METHODS: Sixty-four cases who received LASIK were divided into 4 groups by different binoeular diopter with the binocular aniserkonia (BA) designed by Liugeping and BA. The patients were tested on 6 months before and after the operation respectively for studing the relationship between the post-operative BA and steropsis. RESULTS: When the binocular diopter difference was < or = 2.5 D, there was no significant difference between the preoperative and postoperative BA. When the diopter difference was > 2.50 D, the incongruons images of simultaneous perception and stereoscopic vision after operation had significant divergence compared with those before the operation. The postoperative stereopsis was closely related to binocular vision. CONCLUSION: LASIK can not only reduce the BA of high myopic anisome tropia patients to a range that can be endured, but also be helpful to restore the stereopsis. Moreover, the better the postoperative binocular vision, the patients have the finer the stereopsis will be.

Adult↗
PubMed1993

The effect of disparity on motion coherence.

Many moving plaid stimuli are ambiguous, and perception switches between a coherent plaid pattern and two transparent gratings. Here, experiments are reported that examined the effect of stereodepth between the two gratings of the moving plaid stimulus on the perception of coherence or motion transparency. Increasing disparity increased the percentage of time that two independently drifting transparent gratings were perceived. This was studied for plaids with various levels of intersection luminance. Using intersection luminances beyond conditions of physical transparency increased the percentage of time that one coherent plaid was seen. These two opposing influences could be pitted against each other to achieve constant levels of coherence. An adaptation paradigm was also used in which observers adapted to a stationary stimulus with either zero, crossed or uncrossed disparity between the gratings, and then indicated the occurrence of coherence and motion transparency in test stimuli of drifting plaids with zero, crossed or uncrossed disparity. Adaptation to crossed and uncrossed stereo-depth increased relative perceived coherence equally, especially for zero test disparity. An analysis of the length of the episodes of coherence and motion transparency indicated that the effect of adaptation was to decrease the length of motion transparency episodes, while the length of coherence episodes did not change. It is concluded that mechanisms involved in the processing of stereo-depth must have an input to the integration stage of the motion channel and that pattern and component motion mechanisms can operate quite independently.

Adaptation, Ocular↗
PubMed1999

Visual processing and dyslexia.

Magnocellular-pathway deficits have been hypothesized to be responsible for the problems experienced by dyslexic individuals in reading. However, research has yet to provide a detailed account of the consequences of these deficits or to identify the behavioural link between them and reading disabilities. The aim of the present study was to determine the potential consequences of the magnocellular-pathway deficits for dyslexics in a comprehensive range of visual tasks. Dyslexics and nondyslexics were compared on their ability to (i) perform vernier-acuity and orientation-acuity tasks; (ii) perceive motion by using a range of measures common in the psychophysical literature (Dmin, Dmax, and global coherence); and (iii) perceive shapes presented in random-dot stereograms at a range of disparity pedestals, thereby dissociating stereopsis from vergence control. The results indicated no significant differences in performance between the dyslexic and nondyslexic subjects in terms of the visual-acuity measures. In general, dyslexics performed relatively poorly on measures of motion perception and stereopsis, although when considered individually some of the dyslexics performed better than some of the controls. The poor performance of the dyslexics in the stereo-gram tasks was attributable to a subgroup of dyslexics who also appeared to have severe difficulty with the motion-coherence task. These data are consistent with previous evidence that some dyslexics may have deficits within the magnocellular visual pathway.

Adolescent↗
PubMed2003

Luminance gradient can break background-independent lightness constancy.

A display with a luminance gradient was shown to induce a strong lightness illusion (Logvinenko, 1999 Perception 28 803-816). However, a 3-D cardboard model of this display was found to produce a much weaker illusion (less than half that in the pictorial version) despite the fact that its retinal image is practically the same. This is in line with the hypothesis that simultaneous lightness contrast is solely a phenomenon of pictorial perception (Logvinenko et al, 2002 Perception 31 73-82). The residual lightness illusion in the 3-D model can be accounted for by the fact that this model is a hybrid display. Specifically, while it is a real object, a pictorial representation (of the illumination gradient) is superimposed on it. Thus, lightness in the 3-D display is a compromise between two opposite tendencies: the background-independent lightness constancy and the lightness illusory shift induced by the luminance gradient.

Adolescent↗
PubMed1992

Simple-pooling of unidirectional motion predicts speed discrimination for looming stimuli.

Looming objects comprise many 2D unidirectional motion elements changing over time. However, observers assign a single 3D speed to looming objects, not many independent unidirectional speeds to different regions of the object. These experiments examined speed discrimination for looming stimuli to illuminate the mechanisms underlying the perception of 3D motion. Speed discrimination thresholds for looming displays were comparable to those of fronto-parallel translating and rotating displays (approximately 5%), and thresholds were predicted from the simple linear combination of 2D unidirectional thresholds. These results suggest that 2D unidirectional motion and looming motion are not independent: the simple pooling of unidirectional motion units limits sensitivity to looming stimuli. These results do not support the notion that the visual system directly encodes relative motion within a distinct channel.

Depth Perception↗
PubMed1978

Two dimensionality of the correspondence process in apparent motion.

A fundamental process underlying motion perception is the matching of corresponding elements in different views. In this correspondence process spatial separation between elements plays a major role. The relevant separation is shown by the current study to be the two-dimensional, uninterpreted distance, a finding that has an implication to the level at which the correspondence process is carried out. The current findings are compared with earlier results concerning 'optimality' of apparent motion to conclude that optimality cannot serve as a measure for the correspondence strength.

Depth Perception↗
PubMed2000

Does face recognition rely on encoding of 3-D surface? Examining the role of shape-from-shading and shape-from-stereo.

It is now well known that processing of shading information in face recognition is susceptible to bottom lighting and contrast reversal, an effect that may be due to a disruption of 3-D shape processing. The question then is whether the disruption can be rectified by other sources of 3-D information, such as shape-from-stereo. We examined this issue by comparing identification performance either with or without stereo information using top-lit and bottom-lit face stimuli in both photographic positive and negative conditions. The results show that none of the shading effects was reduced by the presence of stereo information. This finding supports the notion that shape-from-shading overrides shape-from-stereo in face perception. Although shape-from-stereo did produce some signs of facilitation for face identification, this effect was negligible. Together, our results support the view that 3-D shape processing plays only a minor role in face recognition. Our data are best accounted for by a weighted function of 2-D processing of shading pattern and 3-D processing of shapes, with a much greater weight assigned to 2-D pattern processing.

Adolescent↗
PubMed1996

Metamerisms in Structure-from-motion perception.

As a three-dimensional object is moving through our world, we generally obtain a vivid impression of both its structure and its motion through space. The time-course of two-dimensional projections of the scene (optic flow) is important in conveying this three-dimensional information to us. The extent to which we can solve this specific inverse problem, i.e. infer a three-dimensional scene from two-dimensional flow, depends on the accuracy with which the required flow characteristics are processed by our visual system. In adequate two-dimensional processing can lead to incomplete representations of the three-dimensional world (three-dimensional metric information is lost). Then the motion and structure of objects can no longer be recovered uniquely. Consequently, metameric classes of three-dimensional representations arise (e.g. only affine properties are conserved). this study investigates under what conditions we find metameric combinations of the perceived attitude and perceived rotation of a plane. Our subjects are presented with stimuli consisting of two horizontally separated planar patches rotating back and forth in depth about vertical axes. Subjects are required to match both the attitude and the rotation magnitude of these two patches. We vary the attitude from 15 to 60 deg vertical slant, and the rotation magnitude from 28 to 98 deg. We find that the matched slant and rotation settings vary widely. For high slant values and for small rotations, attitude and rotation settings become highly correlated, suggesting metamery. For low slant values and for large rotations, the correlation almost disappears, suggesting that both quantities are estimated independently and uniquely. Our paradigm reveals that with one task and one type of stimulus a gradual transition occurs from unique settings (metric representations) to metameric classes of settings (e.g. affine representations).

Depth Perception↗
PubMed2003

T-junctions and perceived slant of partially occluded surfaces.

Häkkinen and Nyman (1997 Perception 26 29-38) reported that perceived slant is reduced when occlusion is a possible interpretation for the visual system. We present data from three experiments that confirm and expand on their finding. Our stimuli consisted of four types of stereograms depicting white central rectangles flanked on either side by two grey rectangles. The central white rectangles varied in height, thus manipulating the polarity of the T-junction information between the central and flanking rectangles. Perceived slant was smallest or not apparent when T-junction information indicated the central rectangles were nearer than the flanking rectangles and greatest when T-junction information indicated a farther central rectangle. Slant estimates for a stimulus containing a subjective pacmen-induced central rectangle were biased towards a depth step when an occlusion interpretation was possible.

Depth Perception↗
PubMed2002

Three-systems theory of human visual motion perception: review and update: comment.

This comment addresses two issues raised by Lu and Sperling [J. Opt. Soc. Am. A 18, 2331 (2001)]. These authors stated that stereomotion (movement of binocular disparity) is processed exclusively by a third-order motion system that involves feature tracking. This comment discusses evidence that clearly shows that stereomotion is processed by a low-level mechanism that does not track features. Lu and Sperling also claimed that motion signals from binocular rivalry have confounded many stereomotion experiments in the past. This comment discusses how stimuli employed in most previous studies of stereomotion processing would not produce rivalry.

Depth Perception↗
PubMed1978

Stereopsis and spatial perception in amblyopes and uncorrected ametropes.

Amblyopes and nonamblyopes were compared on 2 tests of spatial perception. One, the Titmus stereotest, provided only disparity cues and thus measured pure stereopsis. The other, the 3-rods test, provided a variety of monocular and binocular cues and measured the precision of distance discrimination. On both tests the amblyopes were significantly worse than nonamblyopes with equivalent acuity deficits. The Titmus stereotest was found to be an effective means of screening for amblyopia. The results of the distance discrimination test are discussed in terms of their clinical and physiological implications.

Adult↗
PubMed2002

When feeling is more important than seeing in sensorimotor adaptation.

Perception and action are based on information from multiple sensory modalities. For instance, both vision and proprioception provide information about hand position, and this information is integrated to generate a single estimate of where the hand is in space. Classically, vision has been thought to dominate this process, with the estimate of hand position relying more on vision than on proprioception. However, an optimal integration model that takes into account the precision of vision and proprioception predicts that the weighting of the two senses varies with direction and that the classical result should only hold for specific spatial directions. Using an adaptation paradigm, we show that, as predicted by this model, the visual-proprioceptive integration varies with direction. Variation with direction was so strong that, in the depth direction, the classical result was reversed: the estimate relies more on proprioception than on vision. These results provide evidence for statistically optimal integration of information from multiple modalities.

Adaptation, Physiological↗