Catching and matching bars with different orientations

The hypothesis that perception enslaves action is examined by assessing whether systematic distortions in perceptual judgments are reflected by inaccuracies in catching. In the first experiment, participants had to align manually the orientation of a reference bar placed at different distances in the frontoparallel plane. In the second experiment participants had to catch differently orientated moving bars, which became invisible at different distances from the interception point. In the matching experiment, systematic errors in the alignment of orientation were found in particular for oblique orientations, the magnitude of which increased with increasing distance of the reference bar. The inaccuracies in the final hand orientation during the catching task, however, did not mirror this pattern of deviations. The findings are interpreted to be more consistent with recent views that vision for perception (i.e., matching) and vision for action (i.e., catching) are dissociated than with the view that perception enslaves action.     

Perception of depth: Processing of simple positional disparity as a function of viewing distance

Dependency of perceived depth (relative to the fixation point) on disparity, viewing distance, and the type of the stereoscopic stimulus was investigated. Nearly complete constancy of depth, as required for a veridically matched perception, was observed only at small disparity values and with the larger square-formed stimulus; under these conditions, perceived depth corresponded well with real depth intervals for close viewing distances. Additionally, a model for perceptual processing of both variables, disparity and viewing distance, was applied to the data.     

The influence of restricted viewing conditions on egocentric distance perception: implications for real and virtual indoor environments

We carried out three experiments to examine the influence of field of view and binocular viewing restrictions on absolute distance perception in real-world indoor environments. Few of the classical visual cues provide direct information for accurate absolute distance judgments to points in the environment beyond about 2 m from the viewer. Nevertheless, in previous work it has been found that visually directed walking tasks reveal accurate distance estimations in full-cue real-world environments to distances up to 20 m. In contrast, the same tasks in virtual environments produced with head-mounted displays (HMDs) show large compression of distance. Field of view and binocular viewing are common limitations in research with HMDs, and have been rarely studied under full pictorial-cue conditions in the context of distance perception in the real-world. Experiment 1 showed that the view of one's body and feet on the floor was not necessary for accurate distance perception. In experiment 2 we manipulated the horizontal and the vertical field of view along with head rotation and found that a restricted field of view did not affect the accuracy of distance estimations when head movement was allowed. Experiment 3 showed that performance with monocular viewing was equal to that with binocular viewing. These results have implications for the information needed to scale egocentric distance in the real-world and reduce the support for the hypothesis that a limited field of view or imperfections in binocular image presentation are the cause of the underestimation seen with HMDs.     

Stereoscopic visual displays: Principles,viewing devices,alignment procedures

The principle of binocular (stereoscopic) depth perception is that the visual system interprets the slight differences between the views seen by the two eyes as depth cues. In computer-generated displays, two slightly different images are produced on the left and right halves of the display surface and viewed by a prism, mirror, or binoculars system that delivers the appropriate image to each eye. The prism system is the simplest, the mirror system gives the best optical quality, and the binoculars system is useful for producing large apparent images from small display surfaces. All three systems can be adapted for group viewing and all require careful alignment (null adjustment of accommodative distance and vergence distance). Objective and subjective methods of alignment are described.     

Visual and haptic matching of perceived orientations of lines

In this study we investigated the perception and production of line orientations in a vertical plane. Previous studies have shown that systematic errors are made when participants have to match oblique orientations visually and haptically. Differences in the setup for visual and haptic matching did not allow for a quantitative comparison of the errors. To investigate whether matching errors are the same for different modalities, we asked participants to match a visually presented orientation visually, haptically with visual feedback, and haptically without visual feedback. The matching errors were the same in all three matching conditions. Horizontal and vertical orientations were matched correctly, but systematic errors were made for the oblique orientations. The errors depended on the viewing position from which the stimuli were seen, and on the distance of the stimulus from the observer.     

Organizational factors and the perception of motion in depth

When two stationary, stereoscopically separated targets are viewed in a completely dark surround, and no cues concerning their egocentric distances from the observer are salient, the farther target tends to be seen at the same distance it would have assumed if it were by itself. The nearer target is seen as being closer than it would have been if seen alone. The present studies extend this previous finding (now termed thefar-anchor effect) into the domain of targets that move in stereoscopic space. Observers viewed two small illuminated targets, which began at either the same or different stereoscopic distances. One of the targets was moved in depth and the observers identified the target that appeared to move. Conditions varied according to the initial depth location of the moving target. Significantly more correct responses were reported when the nearer target moved than when the farther one moved, consistent with the hypothesis that the perception of motion in depth is affected by the aforementioned perceptual anchoring effect of the farther target.     

True three-dimensional displays that allow viewers to dynamically shift accommodation, bringing objects displayed at different viewing distances into and out of focus.

Under natural viewing conditions, viewers do not just passively perceive. Instead, they dynamically scan the visual scene by shifting their eye fixation and focus between objects at different viewing distances. In doing so, the oculomotor processes of accommodation (eye focus) and vergence (angle between lines of sight of two eyes) must be shifted synchronously to place new objects in sharp focus in the center of each retina. Accordingly, nature has reflexively linked accommodation and vergence, such that a change in one process automatically drives a matching change in the other. Conventional stereoscopic displays force viewers to try to decouple these processes, because while they must dynamically vary vergence angle to view objects at different stereoscopic distances, they must keep accommodation at a fixed distance--or else the entire display will slip out of focus. This decoupling generates eye fatigue and compromises image quality when viewing such displays. In an effort to solve this accommodation/vergence mismatch problem, we have built various prototype displays that can vary the focus of objects at different distances in a displayed scene to match vergence and stereoscopic retinal disparity demands and better simulate natural viewing conditions. By adjusting the focus of individual objects in a scene to match their stereoscopic retinal disparity, the cues to ocular accommodation and vergence are brought into agreement. As in natural vision, the viewer brings different objects into focus by shifting accommodation. As the mismatch between accommodation and vergence is decreased, natural viewing conditions are better simulated and eye fatigue should decrease.     

Perception of visual inclination in a real and simulated urban environment

The perceived inclination of slopes is generally overestimated. We claim that overestimation depends on the use of impoverished stimuli and on the distance between the observer and an inclined surface. In experiment 1, participants reported the perceived inclination of a set of urban roads from two different viewing distances. Observers did not overestimate the perceived inclination of slopes when they saw roads from the shorter viewing distances, whereas they slightly overestimated the perceived inclination of slopes from the farther distance. In experiment 2, participants reported the perceived inclination of a set of stereoscopic slides representing the same urban roads as in experiment 1. Here, observers did not overestimate the perceived inclination of slopes when the projected stereoscopic image contained horizontal disparity and simulated the shorter viewing distance; while they revealed a slight overestimation from the farther distance. We found always overestimation when the binocular image did not contain horizontal disparity, independently from the viewing distance. In conclusion, slopes are overestimated when (a) horizontal disparity is absent, and (b) the viewing distance is increased.     

Slope estimation and viewing distance of the observer

The overestimation of geographical slant is one of the most sizable visual illusions. However, in some cases estimates of close-by slopes within the range of the observer’s personal space have been found to be rather accurate. We propose that the seemingly diverse findings can be reconciled when taking the viewing distance of the observer into account. The latter involves the distance of the observer from the slope (personal space, action space, and vista space) and also the eye-point relative to the slope. We separated these factors and compared outdoor judgments to those collected with a three-dimensional (3D) model of natural terrain, which was within arm’s reach of the observer. Slope was overestimated in the outdoors at viewing distances between 2 m and 138 m. The 3D model reproduced the errors in monocular viewing; however, performance was accurate with stereoscopic viewing. We conclude that accurate slant perception breaks down as soon as the situation exits personal space, be it physically or be it by closing one eye.     

Weber's illusion and body shape: anisotropy of tactile size perception on the hand

The perceived distance between touches on a single skin surface is larger on regions of high tactile sensitivity than those with lower acuity, an effect known as Weber's illusion. This illusion suggests that tactile size perception involves a representation of the perceived size of body parts preserving characteristics of the somatosensory homunculus. Here, we investigated how body shape is coded within this representation by comparing tactile distances presented in different orientations on the hand. Participants judged which of two tactile distances on the dorsum of their left hand felt larger. One distance was aligned with the proximodistal axis (along the hand), the other with the mediolateral axis (across the hand). Across distances were consistently perceived as larger than along ones. A second experiment showed that this effect is specific to the hairy skin of the hand dorsum and does not occur on glabrous skin of the palm. A third experiment demonstrated that this bias reflects orientation on the hand surface, rather than an eye- or torso-centered reference frame. These results mirror known orientational anisotropies of both tactile acuity and of tactile receptive fields (RFs) of cortical neurons. We suggest that the dorsum of the hand is implicitly represented as wider than it actually is and that the shape of tactile RFs may partly explain distortions of mental body representations.     

Monkeys perceive the orientation of objects relative to the vertical axis

Orientation processing is essential for segmenting contour from the background, which allows perception of the shape and stability of objects. However, little is known about how monkeys determine the degree and direction of orientation. In this study, to determine the reference axis for orientation perception in monkeys, post-discrimination generalization tests were conducted following discrimination training between the 67.5° and 112.5° orientations and between the 22.5° and 157.5° orientations. After discrimination training between the 67.5° and 112.5° orientations, the slope of the generalization gradient around the S⁺ orientation was broad, while the slope was steep after discrimination training between the 22.5° and 157.5° orientations. Comparing the shapes of the gradients indicated that the subjective distance between the 67.5° and 112.5° orientations was small, while the subjective distance between the 22.5° and 157.5° orientation was large. In other words, the monkeys recognized that the former and the latter distances were 45° and 135° across the vertical axis, rather than 135° and 45° across the horizontal axis, respectively. These findings indicate that the monkeys determined the degree and direction of the tilt using the vertical reference.     

Dissociation between location and shape in visual space

There are often large perceptual distortions of shapes lying on the ground plane, even in well-lit environments. These distortions occur under conditions for which the perception of location i saccurate. Four hypotheses are considered for reconciling these seemingly paradoxical results, after which 2 experiments are reported that lend further support to 1 of them--that perception of shapeand perception of location are sometimes dissociable. The 2 experiments show that whereas perception of location does not depend on whether viewing is monocular or binocular (when other distance cues are abundant), perception of shape becomes more veridical when viewing is binocular. This means that perception of shape is not fully constrained by the perceived locations of the vertices that define the shape.     

The induced effect,vertical disparity,and stereoscopic theory

The induced effect is an apparent slant of a frontal plane surface around a vertical axis, resulting from vertical magnification of the image in one eye. It is potentially important in suggesting a role for vertical disparity in stereoscopic vision, as proposed by Helmholtz. The paper first discusses previous theories of the induced effect and their implications. A theory is then developed attributing the effect to the process by which the stereoscopic response to horizontal disparity is scaled for viewing distance and eccentricity. The theory is based on a mathematical analysis of vertical disparity gradients produced by surfaces at various distances and eccentricities relative to the observer. Vertical disparity is shown to be an approximately linear function of eccentricity, with a slope or gradient which decreases with observation distance. The effect of vertical magnification on such gradients is analyzed and shown to be consistent with a change in the eccentricity factor, but not the distance factor, required to scale horizontal disparity. The induced effect is shown to be an appropriate stereoscopic response to a zero horizontal disparity surface at the eccentricity indicated. However, since extraretinal convergence signals provide conflicting evidence about eccentricity, they may attenuate the induced effect from its mathematically predicted value. The discomfort associated with the induced effect is attributed to this conflict.     

Picture perception: An analysis of visual compensation

Although geometric information is altered when a picture’s viewing point is changed, such changes often do not affect perception. Two experiments assessed pictorial perception relative to the distortions introduced by viewing point dislocation. Results provide a psychophysical demonstration of pictorial compensation and suggest that it is based on the discrepancy between the actual and an assumed-correct viewing position. An explanation of pictorial compensation is offered that could be applied to direct picture perception and to picture-in-a-picture perception.     

On the interactive influence of facial appearance and explicit knowledge in social categorization

Although people form impressions of others with ease, sometimes one's initial perceptions of individuals conflict with what one knows about them. Here, we aimed to investigate the process by which explicit knowledge about people interacts with initial perceptions on the basis of cues from facial appearance. Participants memorized the sexual orientations of men's faces wherein half of the targets were encoded with a sexual orientation opposite to their actual orientation. Subsequent categorization showed that perceivers favored appearance‐based information when temporally constrained but favored explicit knowledge about group membership with increased viewing time. Additionally, real‐time measures of participants' categorizations showed greater vacillation between appearance‐based cues and explicit knowledge as viewing time increased. These findings suggest that explicit knowledge does not simply overrule appearance‐based cues past a particular threshold but that the two may interact recurrently with top‐down knowledge directing attention and perception at later processing. Copyright © 2014 John Wiley & Sons, Ltd.     

Pictorial perspective: perception of size, linear, and texture perspective in children and adults

Perception of size, linear, and texture perspective was investigated in third-grade and sixth-grade children and in college adults in three separate studies. A matching task required the observer to choose from a set of four alternative real scenes the correct match for the test stimulus, which was either a picture or a real scene. Correct performance required that the subject utilize perspective information for both size and distance distance relations. Erroneous choices available to the subject indicated errors in size judgement, in distance judgment, or in both simultaneously. View was either restricted at the correct station point or was free, with head motion. There were no significant effects of grade level. For all three groups, mean percent correct was nearly 100% with the real-scene test stimuli, and significantly below the chance level with the picture test stimuli. Errors in size judgment occurred most frequently, indicating that the geometrically correct rate of perspective convergence was too rapid to be seen by the subjects as perceptually acceptable. With size-perspective information alone, the number of size plus distance errors also increased significantly. There was no significant effect of viewing condition.     

The nature of adaptation in distance perception based on oculomotor cues

In previous work by the senior authors, brief adaptation to glasses that changed the accommodation and convergence with which objects were seen resulted in large alterations in size perception. Here, two further effects of such adaptation are reported: alterations in stereoscopic depth perception and a change when distance is represented by a response of S’s arm. We believe that the three effects are manifestations of one primary effect, an alteration of the relation between accommodation and convergence on the one hand and the distance they represent in the nervous system (registered distance) on the other. This view was supported by the results of two experiments, each of which demonstrated that the alterations in stereoscopic depth perception could be obtained after adaptation periods which had provided no opportunity to use stereoscopic vision, and that the adaptation effect was larger for depth perception than for size perception when it was obtained under the same conditions; the latter finding was expected if both effects resulted from the same change in registered distance. In three of the five experiments here reported, the variety of cues that could represent veridical distance during the adaptation period was limited. In one condition of adaptation, only the pattern of growth of the retinal images of objects that S approached and the kinesthetic cues for S’s locomotion served as cues to veridical distance. In two other conditions S remained immobile. In one of these, only the perspective distortion in the projection of the scene that S viewed mediated veridical distance, and in the other one familiar objects of normal size were successively illuminated in an otherwise totally dark field, conditions from which opportunities to use stereoscopic vision were again absent. After exposure to each of these adaptation conditions, adaptive changes in perceived size and larger ones in perceived stereoscopic depth were obtained. Because we found that familiar size may serve as the sole indicator of veridical distance in an adaptation process, we concluded that it can function as a perceptual as distinguished from an inferential cue to distance.     

Magnification rate of objects in a perspective image to fit to our perception

Abstract: A landscape photograph may give a different impression from that formed at the real scene, with respect to the size and distance of objects. Researchers have reported that the perceived sizes and distances of objects in a photograph are not identical to those in a real space. In order to develop a method to create a graphic image that is close to our visual impression as seen in the real space, two experiments were conducted. In Experiment 1, we examined how the magnification rate of the perceived size to the object size on the retina varied with the viewing distance (range was from 1 m to 10 m). In Experiment 2, we examined whether transformation based on the magnification rate is effective for creating an image that matches the perceived size of the object at the scene. Our results indicate that the magnification rate is useful for transforming the perspective image to match our perception of the objects regardless of the viewing distance.     

Optic array determinants of apparent distance and size in pictures

This study explored whether special mechanisms are operative in picture perception to correct for the distortion that occurs when pictures are viewed from the wrong station point. Five photographs were taken of a layout composed of two same-sized dolls positioned at different distances on a flat untextured ground. Perspective differences existed between the photographs as a function of varying the distance of the camera to the layout. Each picture was viewed from five station points along the normal by 12 adults who estimated the relative magnitude of the depth interval between the dolls and judged whether the rear doll was objectively smaller, larger, or the same size as the front doll. No evidence was found of a compensation mechanism operating to stabilize the pictured layout. Distance and size judgments were affected in a manner that was consistent with what would occur if an actual layout and the conditions under which it were viewed were similarly transformed.     

Introduction: A Cognitive Science Slam in Honor of Guy Van Orden

Illusory depth perception experienced in driving simulators is afforded by monocular depth information contained in visual displays. Presumably binocular convergence and binocular disparity, though useful for depth perception in real environments, may poorly contribute to illusory depth in a driving simulator. Instead, they may generate conflicting information by revealing the distance of the display screen and its flatness. Nevertheless, illusory depth induced by monocular information contained in visual displays usually produces enough immersion and realism to create the illusion of driving in a real environment.

Many authors have noted improved depth perception in paintings, photographs, and even in drawings when viewed monocularly. However, this effect, known as monocular advantage, has never been explored in driving simulation. The purpose of this experiment was to assess whether the effect might exist in driving simulation. It was expected that drivers would perceive distances in depth better and more accurately with a monocular than with a binocular viewing of the display. Distance estimates were evaluated for two types of driving maneuvers referred to as alignment and bisection. Results showed that when significant performance differences between monocular and binocular viewing conditions occurred, target cars were perceived farther in depth and more accurately using monocular vision.

Alternative viewing conditions using both eyes are discussed at the end of the article.