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At least 235 records · Page 13Linked to original sources
PubMed1995

Influence of flicker on perceived size and depth.

Previous research (e.g., Wong & Weisstein, 1984a, 1985) has shown that flickering stimuli appear to be more distant than nonflickering stimuli at the same physical distance. Given this relation between flicker and perceived depth, inappropriate constancy scaling theories predict that flickering stimuli should be perceived as larger than nonflickering ones. In contrast, links between flicker and motion perception suggest that flickering stimuli should be perceived as smaller than nonflickering ones. Two experiments tested these contrasting predictions. In Experiment 1, 22 subjects compared flickering and nonflickering vertical lines and reported that the flickering stimulus appeared significantly smaller than the nonflickering one. In Experiment 2, 21 subjects reported that the stimuli used in Experiment 1 produced depth effects similar to those reported in previous experiments: flickering stimuli were perceived as more distant than nonflickering ones. The observed effect of flicker on perceived size was contrary to predictions from inappropriate constancy scaling theory, but consistent with views that motion and flicker are processed by the same pathway.

Adolescent↗
PubMed1984

Visually perceiving distance: a comment on Shebilske, Karmiohl, and Proffitt (1983).

Shebilske, Karmiohl, and Proffitt (1983) interpret their data as showing that (a) the reference tonus level of the extraocular muscles controlling vergence is affected by everyday conditions of close viewing, and (b) this naturally induced phoria affects the visual perception of distance under natural viewing conditions. We note that these interpretations do not fully concur with the data presented--for example, the second conclusion favorably conflates partial results from two separate experiments--and we identify a number of confoundings that reduce the likelihood that the reported inaccuracies in distance judgments were due to variations in efference.

Distance Perception↗
PubMed1987

Art and the oculomotor system: perspective illustrations evoke vergence changes.

When a painting or drawing is viewed monocularly and fixation alternated between points that are at different implied distances from the observer, the covered eye usually makes vergence movements that are directionally appropriate for the indicated depth differences. These vergence changes evoked by perspective artwork vary greatly in magnitude and consistency from one illustration to the next: some drawings and paintings lead to convergence-divergence changes smaller than would be appropriate for the illustrated content, if seen from the implied viewing distance; others are supernormal stimuli, evoking inappropriately large vergence changes in all observers tested.

Adolescent↗
PubMed1993

Perceiving the affordance of contact in four- and five-month-old infants.

The focus of this study was on the ability of infants to perceive whether an object is positioned at a distance that would make contact possible. As a toy was presented, sometimes within and sometimes beyond reach, the initiation of reaching and leaning forward was scored. Infants were divided into leaning and nonleaning groups. Both leaning and nonleaning 5-month-olds changed their behavior dramatically when the object was placed beyond, as opposed to within, reach. The nonleaners showed a decline in reaching when this boundary for contact was crossed. The "leaners" did not; rather, they began to lean forward. These results suggest that 5-month-olds use information for the affordance of contact. 4-month-olds provided less evidence that arm length regulates reaching. 5-month-old infants acted as if they not only had some sensitivity to the absolute distance of an object but also to the effect that leaning forward has on their ability to make contact with a distant object.

Cognition↗
PubMed1986

Shape constancy and polar perspective.

The distortion of polar perspective depends on the depth of the tridimensional shape and on the observation distance. In four experiments using 54 undergraduates as subjects, we found that a compensation process which takes depth and observation distance into account corrects for such distortions. Compensation was demonstrated in experiments in which deceptive information on depth and on observation distance was provided. The result was distortions of the perceived shapes that would be expected if compensation were based on the deceptive information.

Cues↗
PubMed1976

An investigation of the relationship between viewing condition and preference for true and modified linear perspective and adults.

In four experiments, pictures varying in degree of perspective convergence from linear to parallel were observed under the following conditions: at an arbitrary station point, at correct station points, and with unconstrained view. Adults were asked to rank the pictures from the most to least natural and realistic-looking picture or from the most to the least accurate drawing. Subjects nearly always chose the parallel perspective pictures as most preferred and the linear perspective pictures as least preferred. Intermediate degrees of convergence were ranked accordingly. Results were interpreted in light of an argument for a pictorial station poing independent of the correct center of projection for a picture. Since this station point was calculated to be at a distance at least 10 times as great as the object is large, its assumption for pictorial viewing was termed the "Zoom "effect.

Adult↗
PubMed1979

Estimation of distances of recorded sounds presented through headphones.

Intermittent sounds generated at 270 degrees azimuth and from distances ranging from 2 to 10 feet were recorded on magnetic tape and played back to listeners via headphones. Loudness cues for relative distance were eliminated at the time of recording. Listeners were required to estimate the apparent distance of the recorded sounds when heard monoaurally and binaurally. Most subjects estimated the order of distances correctly. Distance estimations were as proficient when listening monaurally as when listening binaurally. Performance was more accurate for high-pass (greater than 4.0 kHz) noise bursts than for low-pass (less than 1.0 kHz) noise bursts. In a second study, broad-band noise bursts were recorded from azimuthal positions of 360 degrees, 330 degrees, 300 degrees and 270 degrees again at distances ranging from 2 to 10 feet. Estimations of the distances of the sounds, presented via headphones, were most proficient when azimuthal position of the original stimuli was 330 degrees.

Acoustic Stimulation↗
PubMed1984

[Binocular functions in unilateral pseudophakia].

71 patients (average age 64 years) were examined for binocular vision after unilateral posterior chamber lens implantation. Average visual acuity in the pseudophacic as well as the phacic eyes was 0.8. Intact stereoscopic dose-up and long-distance vision was found in 85% of the cases. Patients with vertical phorias or moderately decreased visual acuity more often presented impaired binocular functions. Further investigations will be carried out.

Aged↗
PubMed1990

Perceptual information for the timing of interceptive action.

Time-to-contact is an important quantity for controlling activities which involve the timing of interactions with objects and surfaces in motion relative to an observer. Two alternative means for obtaining perceptual information that might be used to obtain the time-to-contact required to correctly time an interaction have been contrasted: a method based on the perception of distance and velocity, and a method due to Lee involving a perceptual variable called tau. A monocular version of the first method is presented and shown to place a highly unrealistic and arbitrary limitation on the capabilities of the visual system. The second method is reviewed and its limitations discussed. Several means by which these limitations can be overcome are presented. Recently reported results from experiments which involved catching self-luminous balls in the dark are interpreted in terms of timing information available to the subject, and the notions of intermodal and multimodal timing information are introduced. Finally, the possibility that timing information is available to an observer which does not involve the variable tau is considered. It is concluded that many questions regarding the perception of time-to-contact remain unresolved and that much empirical research remains to be done.

Acceleration↗
PubMed1988

Depth resolution in the pigeon.

Pigeons possess a binocular visual field and a retinal region of higher cellular density pointing to the center of this overlap. These features and the precision of pecking behavior suggest that in this lateral-eyed bird cues other than monocular ones might participate in depth judgements. Pigeons were trained with an operant procedure to discriminate between luminous points differing in depth which appeared to the observer as floating in the dark. The accuracy of depth judgements was found to be a function of the ratio between the interstimulus distance and the mean eyes-to-stimulus distance. In a first test (experiment I) no external binocular disparity cues were available, the animal only seeing one luminous point at a time (near or far). In a second test (experiment II) where binocular disparity cues were available, the animal having this time to discriminate a pair of points placed at equal depth from a pair placed at unequal depths, only one pair being visible at a time, depth resolution did not improve. This suggests that, at least within the range of distances explored, the pigeon has no stereoscopic vision. Notwithstanding this, binocular cues do play a role, since when tests were done comparing binocular with monocular viewing (experiment III), monocular depth resolution was significantly worse.

Animals↗
PubMed1992

The role of binocular vision in prehension: a kinematic analysis.

This study examined the contribution of binocular vision to the control of human prehension. Subjects reached out and grasped oblong blocks under conditions of either monocular or binocular vision. Kinematic analyses revealed that prehensile movements made under monocular viewing differed substantially from those performed under binocular conditions. In particular, grasping movements made under monocular viewing conditions showed longer movement times, lower peak velocities, proportionately longer deceleration phases, and smaller grip apertures than movements made under binocular viewing. In short, subjects appeared to be underestimating the distance of objects (and as a consequence, their size) under monocular viewing. It is argued that the differences in performance between the two viewing conditions were largely a reflection of differences in estimates of the target's size and distance obtained prior to movement onset. This study provides the first clear kinematic evidence that binocular vision (stereopsis and possibly vergence) makes a significant contribution to the accurate programming of prehensile movements in humans.

Adult↗
PubMed1982

[Dynamic wallpaper phenomenon and fusional hysteresis].

Two experiments were conducted with six and three subjects, respectively, to examine the "dynamic" wallpaper phenomenon in which the apparent location of a uniform repeating pattern shifted abruptly at a certain convergence distance when the pattern was viewed with the gradual change of convergence. Experiment 1 demonstrated that the critical convergence distances (shift points), at which the apparent location of the pattern shifted, differed between the two directions of the change of convergence, converging and diverging. It was greater in the diverging condition than in the converging condition. This fact shows a tendency to keep the same fusional state as far as possible when the convergence changes gradually. Experiment 2 showed that the difference of the critical convergence distance between the converging and diverging conditions is systematically related to the convergence level, that is, the difference increased as the convergence angle increased. The implications of the results of the two experiments were discussed in the context of the fusional hysteresis.

Adult↗
PubMed1980

[Effect of age on visual functions].

The differential color-distinquishing threshold, functional reserves, visual acuity, distance to the nearest point of clear vision and positive part of absolute accomodation were measured in working people in active age. A certain deterioration of these visual parameters with advancing age was recorded, which was practicall manifested by decreased ability for fine distinquishing of details, color and relief, when continuous work at short distance was performed. The greater variations in the functional state of vision at the of the working day in elderly workers require measures to be taken to alleviate work, in conformity with the age characteristics of the visual functions.

Accommodation, Ocular↗
PubMed1993

The effects of size, clutter, and complexity on vanishing-point distances in visual imagery.

The portrayal of vanishing-point distances in visual imagery was examined in six experiments. In all experiments, subjects formed visual images of squares, and the squares were to be oriented orthogonally to subjects' line of sight. The squares differed in their level of surface complexity, and were either undivided, divided into 4 equally sized smaller squares, or divided into 16 equally sized smaller squares. Squares also differed in stated referent size, and ranged from 3 in. to 128 ft along each side. After subjects had formed an image of a specified square, they transformed their image so that the square was portrayed to move away from them. Eventually, the imaged square was portrayed to be so far away that if it were any further away, it could not be identified. Subjects estimated the distance to the square that was portrayed in their image at that time, the vanishing-point distance, and the relationship between stated referent size and imaged vanishing-point distance was best described by a power function with an exponent less than 1. In general, there were trends for exponents (slopes on log axes) to increase slightly and for multiplicative constants (y intercepts on log axes) to decrease as surface complexity increased. No differences in exponents or in multiplicative constants were found when the vanishing-point was approached from either subthreshold or suprathreshold directions. When clutter in the form of additional imaged objects located to either side of the primary imaged object was added to the image, the exponent of the vanishing-point function increased slightly and the multiplicative constant decreased. The success of a power function (and the failure of the size-distance invariance hypothesis) in describing the vanishing-point distance function calls into question the notions (a) that a constant grain size exists in the imaginal visual field at a given location and (b) that grain size specifies a lower limit in the storage of information in visual images.

Adult↗
PubMed1992

Position-linked interference in forming simple visual groups.

Experiments with 2-element visual groups reveal a form of interference that has several interesting properties. Observers judged the orientation of an imaginary line formed by 2 pixels (the target) while attempting to ignore a third pixel (the noise). Noise interfered with performance, even when it was made distinct from the target in various ways. This interference was strongly position linked; a single equation described the interference pattern for many different target-noise configurations. Maximum interference was observed not when the noise was closest to the target but when it was at a distance of half the separation between target pixels. Some initial findings were consistent with the idea that visual grouping reflects the operation of visual channels with Gabor-like receptive-field profiles. But subsequent results implicated processes that automatically construct visual boundaries.

Adult↗
PubMed1993

A Müller-Lyer-type illusion of egocentric distance with 3D convex and concave objects.

An illusion of egocentric distance with concave and convex objects at a distance of 135 cm is reported. When the centre of a concave object was viewed with both eyes its surface appeared nearer than the centre of the surface of a convex object at the same distance. The distortion was about two per cent of the viewing distance with right-angle objects and about five per cent with hemicylindrical objects. The distortion was slightly reduced when size cues for distance were attached to the surfaces of the objects, absent with monocular viewing, greater with convex than with concave objects, and occurred with the generally convex surface of a model human face. Possible explanations of the findings are discussed.

Defense Mechanisms↗