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At least 1,099 records · Page 61Linked to original sources
PubMed1994

Convergence as a cue for distance.

Binocular eye movements were measured in subjects experiencing the wallpaper illusion. It was found that a physical displacement of the fixation point by more than 1 m out of the plane of apparent localisation of the strips had no influence on the illusory location of these strips. Hence, illusory localisation in the wallpaper illusion is independent of the actual magnitude of the subject's convergence angle, once the illusion has come into existence. This result suggests that convergence does not serve as a source of information about apparent distance, at least in the wallpaper illusion.

Adult↗
PubMed1994

Prospective control in catching by infants.

Catching a moving object requires the ability to predict the future trajectory of the object. To test whether infants can use visual information predictively, reaching for a toy moving at different speeds was investigated in six infants around 11 months of age. The toy was occluded from view by a screen during the last part of its approach. Gaze arrived at the exit side of the screen and the hand started to move forward before the toy had disappeared behind the occluder; these actions were prospectively geared to certain times before the toy would reappear. In addition, hand-movement duration was found to be related to the time of reappearance of the toy--the information used to regulate duration of hand movement being picked up before the toy disappeared behind the occluder. In a longitudinal experiment, the development of predictive reaching was investigated in two infants between the ages of 20 and 48 weeks. At all ages studied, gaze anticipated the reappearance of the moving toy. However, anticipation with hand movement of the disappearance of the toy and the ability to gear actions prospectively to the time (instead of distance) the toy was away from certain points on the track developed relatively late and marked the transition to successfully catching faster-moving toys.

Acceleration↗
PubMed1994

Invariance from the Euclidean geometer's perspective.

It is remarkable how well the human visual system can cope with changing viewpoints when it comes to recognising shapes. The state of the art in machine vision is still quite remote from solving such tasks. Nevertheless, a surge in invariance-based research has led to the development of methods for solving recognition problems still considered hard until recently. A nonmathematical account explains the basic philosophy and trade-offs underlying this strand of research. The principles are explained for the relatively simple case of planar-object recognition under arbitrary viewpoints. Well-known Euclidean concepts form the basis of invariance in this case. Introducing constraints in addition to that of planarity may further simplify the invariants. On the other hand, there are problems for which no invariants exist.

Attention↗
PubMed1994

The effect of knowledge of object distance on accommodation during instrument viewing.

We present data in which instrument accommodation was measured while knowledge of object distance was varied. The accommodative feedback loop was 'semiopen'--an intermediate state between the closed-loop and open-loop conditions of previous experiments. The semiopen-loop situation mimicked the degraded-image conditions which are frequently encountered during instrument viewing. The results show that for some subjects knowledge of object distance is a more powerful cue for instrument accommodation than is the optical distance of the object; however, for the majority of subjects this is not the case. We also found that subjects whose accommodation is influenced by knowledge of object distance tend to have a more proximal dark focus than those whose accommodation is independent of knowledge of object distance. We propose that the Mandelbaum effect, in which involuntary accommodation occurs when a transparency is superimposed between the observer and the object of regard, could account for the accommodative behavior of all subjects. However, the Mandelbaum effect would have to be interpreted more broadly than before. In the broader interpretation, the transparency could be cognitive (ie known distance) rather than physical.

Accommodation, Ocular↗
PubMed1994

Factors limiting large-scale localisation.

The mechanisms mediating relative spatial localisation in the visual system are still unclear. There is a growing amount of evidence that this capability is not merely limited by the processing of the front-end visual system. Models of localisation should, therefore, include higher-level processing stages. A careful study of the sources of error in localisation tasks may further our understanding of the nature of these processes. A study is reported in which the possible role of higher-order processing in relative spatial localisation is explicitly addressed. For this purpose the error sources of threshold performance were investigated for two similar relative-spatial-localisation tasks: two-dot separation discrimination and two-dot orientation discrimination. Fovea-centered stimuli with large dot separations were used. The front-end processing for these stimuli is probably identical in both tasks. Hence, differential effects of the variation of the experimental parameters on threshold performance for both tasks may reveal the characteristics of the higher-level processing involved. The effects of dot separation, stimulus orientation, and experimental procedure (single-stimulus binary forced choice versus two-alternative forced choice) on threshold performance for both tasks are reported. The results show that thresholds for both tasks increase proportionally with dot separation. However, separation-discrimination thresholds are always significantly higher than orientation-discrimination thresholds. Thresholds for separation discrimination are independent of stimulus orientation. In contrast, orientation-discrimination thresholds show an oblique effect: thresholds are consistently lower for horizontal stimuli. Both tasks also show a different dependency of threshold behaviour on the experimental procedure. For a horizontal stimulus orientation, separation discrimination is better with an explicit (physical) reference standard, whereas orientation discrimination is better with an implicit referent. These differential effects cannot be explained by any of the known characteristics of the front-end visual system. They suggest that large-scale spatial-localisation performance is probably limited at a processing level at which spatial relations are explicitly represented.

Adult↗
PubMed1994

Visual directions of two stimuli in Panum's limiting case.

Visual directions of the two stimuli in Panum's limiting case with different interstimulus and convergence distances confirmed the predictions from the reformulated Wells-Hering's laws of visual direction. In experiment 1, six observers each converged on the midpoint of the interstimulus axis at 30, 60, and 90 cm from the eyes and adjusted a probe on the fixation plane to be in the same visual direction as that of each stimulus. Visual direction of the far stimulus was always nonveridical whereas that of the near stimulus was veridical only when its retinal disparity was small. In experiment 2, three observers each converged on the intersection of mid-sagittal plane and (a) the frontoparallel plane of the near stimulus, (b) that of the midpoint between the two stimuli, or (c) that of the far stimulus. The midpoint of the interstimulus axis was 60 cm from the eyes. Visual direction of the far stimulus was veridical only with convergence at the far plane. Visual direction of the near stimulus was veridical with convergence at the near plane, and also, only when its retinal disparity was small, with convergence at the two other planes.

Analysis of Variance↗
PubMed1996

Visual control of steering without course information.

An analysis and experimental evidence are presented that the visual control of steering in following a straight demarcated path is possible even when information about the direction of one's travel (course) is not available. Two likely sources of optical information available to observers are considered, bearing and splay, that might be used for steering under these conditions. In an experiment involving a computer-driven driving simulator, observers attempted to steer a straight path while subjected to lateral perturbing forces. When only bearing and its time derivative, motion parallax, were available, performance fell off as expected with the optical gain of motion parallax as the preview distance of the viewing aperture was varied. When splay angle and its time derivative, splay rate, were added to the display, performance generally improved and remained relatively constant with changing distance of the viewing aperture, as expected because of the constant optical gain of splay rate. Making course information available by adding point features to both displays improved steering performance only in the motion-parallax conditions.

Automobile Driving↗
PubMed1996

The role of retinal versus perceived size in the effects of pitched displays on visually perceived eye level.

Visually perceived eye level (VPEL) was measured while subjects viewed two vertical lines which were either upright or pitched about the horizontal axis. In separate conditions, the display consisted of a relatively large pair of lines viewed at a distance of 1 m, or a display scaled to one third the dimensions and viewed at a distance of either 1 m or 33.3 cm. The small display viewed at 33.3 cm produced a retinal image the same size as that of the large display at 1 m. Pitch of all three displays top-toward and top-away from the observer caused upward and downward VPEL shifts, respectively. These effects were highly similar for the large display and the small display viewed at 33.3 cm (ie equal retinal size), but were significantly smaller for the small display viewed at 1 m. In a second experiment, perceived size of the three displays was measured and found to be highly accurate. The results of the two experiments indicate that the effect of optical pitch on VPEL depends on the retinal image size of stimuli rather than on perceived size.

Adolescent↗
PubMed1999

Exocentric pointing in three-dimensional space.

A study is reported of an exocentric pointing task in all three dimensions, in near space, with only two visible luminous objects--a pointer and a target. The task of the subject was to aim a pointer at a target. The results clearly show that visual space is not isotropic, since every set direction appeared to consist of two independent components--one in the projection onto a frontoparallel plane (tilt), the other in depth (slant). The tilt component shows a general trend across subjects, an oblique effect, and can be judged monocularly. The slant component is symmetrical in the mid-sagittal plane, requires the use of binocular information, and shows considerable differences between subjects. These differences seem to depend on the amount of binocular information used by each subject. There was a remarkably high level of consistency in the exocentric pointing, despite the absence of environmental cues. The within-subject consistency in the settings of the pointer corresponds to a consistency of about 1 min of arc in disparity of its tip, even though the pointer and target are separated by more than 5 deg.

Adolescent↗
PubMed1999

Visual measurement of relative distances between three collinear dots rotating in a slanted plane.

Displays consisted of orthographic and perspective projections of three collinear dots rotating rigidly around a fixed centre in a plane slanted 45 degrees in depth. Observers were asked to decide whether the middle of the three dots was exactly centred in 3-D space between the other two dots. The visible rotation segments were 120 degrees, 160 degrees, or 200 degrees and the displacements were 2%, 4%, or 6%. Our untrained observers performed more poorly overall than well-practised observers tested earlier by Lappin and Fuqua (1983 Science 221 480-482). Results of additional manipulations suggested that 2-D image properties played a more important role than acknowledged by Lappin and Fuqua. First, displacement size and the position of the rotation centre produced nonlinear effects. Second, the direction of displacement affected performance. Third, projection type and display type (static snapshots versus elliptic traces) were involved in complex interactions. Clearly, performance was affected by 2-D image properties that should be irrelevant to the calculation of 3-D projective invariants.

Cues↗
PubMed2000

Cleomedes (c. 1st century AD) on the celestial illusion, atmospheric enlargement, and size-distance invariance.

Cleomedes (Kleomedes) is a little-known Greek author (c. 1st century AD) who produced what is probably the earliest extant statement of size-distance invariance. He supported the Stoic philosophy and was concerned to discredit the Epicurean position that we perceive objects as having their true size. He explained the celestial illusion (the apparent enlargement of the sun near the horizon) in two ways: partly as a refractive effect of the atmosphere similar to angular enlargement when looking into water; and partly as a linear enlargement due to increased apparent distance in a misty atmosphere. He is the earliest extant author to offer apparent distance as a clear explanation of the celestial illusion. He attributed these views to Posidonius (c. 135-50 BC). His explanations remained at the geometrical level, and he did not speculate on sensory mechanisms.

Distance Perception↗
PubMed2000

The spatial spread of attentional modulation of the motion aftereffect.

The spatial spread of attentional modulation of selective adaptation was investigated in four experiments in which the duration of the movement aftereffect (MAE) was measured with and without processing of intermittently changing digits at the fixation point. In the first experiment, the effects of diverting attention on MAE duration were found to reduce as the distance between the fixation digits and the inner edge of the surrounding adapt/test grating was increased. A second experiment suggested that eye movements were unlikely to underlie the attentional effects. In experiment 3, the attentional effect stayed constant as the outer diameter of the adapt/test gratings was increased. In experiment 4 (as in experiment 1) the modulatory effects of attention were larger the closer the adapt/test gratings were to the locus of attention, when the area of the grating was held constant but its eccentricity varied. In experiments 1 and 4, an intermittently changing fixation digit was found to reduce MAE durations more than an unchanging digit, even when subjects were not required to process it, suggesting that exogenous as well as endogenous attentional processes modulate early motion processing.

Attention↗
PubMed2002

Global and local contributions to the optical specification of time to contact: observer sensitivity to composite tau.

First-order time remaining until a moving observer will pass an environmental element is optically specified in two different ways. The specification provided by global tau (based on the pattern of change of angular bearing) requires that the element is stationary and that the direction of motion is accurately detected, whereas the specification provided by composite tau (based on the patterns of change of optical size and optical distance) does not require either of these. We obtained converging evidence for our hypothesis that observers are sensitive to composite tau in four experiments involving relative judgments of time to passage with forced-choice methodology. Discrimination performance was enhanced in the presence of a local expansion component, while being unaffected when the detection of the direction of heading was impaired. Observers relied on the information carried in composite tau rather than on the information carried in its constituent components. Finally, performance was similar under conditions of observer motion and conditions of object motion. Because composite tau specifies first-order time remaining for a large number of situations, the different ways in which it may be detected are discussed.

Adolescent↗
PubMed2002

Large-scale visual frontoparallels under full-cue conditions.

We determined the curvature of apparent frontoparallels in a natural scene (a large lawn in broad daylight). Data on frontoparallels in these conditions are very sparse and reveal idiosyncratic curvatures of frontoparallels and irregular variation with distance. We used a method of bisection of linear segments indicated through pairs of stakes at angular separations (from the vantage point) of up to 120 deg. Distances of 2 m and 10 m (in the forward direction) were used. The bisection was carried out by the observer through maneuvering a radio-controlled vehicle carrying a third stake. Four observers participated in the experiment; they had no problems with the task and yielded mutually consistent results. We found that the frontoparallels are significantly curved and are concave towards the observer. Surprisingly, the sign of the curvature is opposite to that found when the frontoparallels are defined through an exocentric pointing task. Available theory (Luneburg's) does not predict this, but the theory is hardly applicable to the case of vision in natural scenes. This interesting discrepancy has not been reported before.

Cues↗
PubMed2003

Spatial reference and scanning with the left and right hand.

Discrepant findings on performance by the two hands in spatial tasks make it difficult to infer spatial coding unambiguously. We tested the hypotheses (a) that the left hand is consistently better in haptic spatial tasks and (b) that adding spatial reference information produces more accurate coding in spatial tasks, independently task and hand effects. Instructions to use external cues from a surrounding frame as well as body-centred cues for reference produced highly significant increases in accuracy in haptic distance and location experiments. The distance experiments showed no hand differences. A small right-hand advantage with longer positioning movements in the recall of locations was significant when combined with left-hand scanning of the frame, but did not relate to reference conditions. Hand use interacted significantly with the location-versus-distance experiments, but showed no interaction with the spatial reference factor, which was highly significant in both experiments. The finding suggests that modes of coding need to be distinguished from cross-lateral effects of sensory input conditions. The study shows that varying reference information offers a potentially useful behavioural tool for distinguishing spatial coding from input and task conditions independently of hand performance. Methodological, practical, and theoretical implications are discussed.

Adolescent↗
PubMed2003

Judging distance across texture discontinuities.

Sinai et al (1998 Nature 395 497-500) showed that less distance is perceived along a ground surface that spans two differently textured regions than along a surface that is uniformly textured. We examined the effect of texture continuity on judged distance using computer-generated displays of simulated surfaces in five experiments. Discontinuities were produced by using different textures, the same texture reversed in contrast, or the same texture shifted horizontally. The simulated surface was either a ground plane or a frontoparallel plane. For all textures and both orientations, less distance was judged in the discontinuous conditions than in continuous conditions. We propose that when a surface contains a texture discontinuity, a small area adjacent to the perceived boundary is excluded from judged distances.

Adult↗
PubMed2003

A comparison of visual and nonvisual sensory inputs to walked distance in a blind-walking task.

Two experiments were conducted in order to assess the contribution of locomotor information to estimates of egocentric distance in a walking task. In the first experiment, participants were either shown, or led blind to, a target located at a distance ranging from 4 to 10 m and were then asked to indicate the distance to the target by walking to the location previously occupied by the target. Participants in both the visual and locomotor conditions were very accurate in this task and there was no significant difference between conditions. In the second experiment, a cue-conflict paradigm was used in which, without the knowledge of the participants, the visual and locomotor targets (the targets they were asked to walk to) were at two different distances. Most participants did not notice the conflict, but despite this their responses showed evidence that they had averaged the visual and locomotor inputs to arrive at a walked estimate of distance. Together, these experiments demonstrate that, although they showed poor awareness of their position in space without vision, in some conditions participants were able to use such nonvisual information to arrive at distance estimates as accurate as those given by vision.

Awareness↗
PubMed2004

The development of distance estimation in optic flow.

In three experiments we tested the ability of children aged 8 to 12 years and adults to locate a target in an optic texture flow projected onto the ground. During the exposure phase, a static target (diode) was lit up at 6 m or 8 m on the ground in front of the subject. During the pointing phase, the subject was asked to indicate the perceived location of the target with a laser pointer as soon as the target was switched off. In the first experiment, during both phases the optic texture (environment) was either motionless or approaching the subject. Results showed that target locations were significantly more underestimated within the moving texture than within the still texture. In the second experiment, a detailed error analysis showed that the differences of performance between children and adults were not due to differences in eye height. Errors can be described by a linear fit with the retinal speed of the optic flow surrounding the targets. Distance judgments improved from the age of 8 years onwards. In the last experiment we found the same kind of results with a receding texture and without stimulation in central vision. Results are discussed in terms of subject's capacity to compensate for the effect of linear vection produced by the optic flow.

Adult↗