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At least 91 records · Page 5Linked to original sources
PubMed1994

[Treatment of fusional disorders in patients with brain damage].

BACKGROUND: We trained fusional convergence systematically using 3 orthoptic devices (fusion trainer, prisms, cheiroscope) in brain damaged patients with a severe deficit of convergent fusion. PATIENTS AND METHODS: 12 patients were selected, 6 with vascular cerebral lesions and 6 with traumatic brain damage. The chronicity (time since lesion) was 15.8 months (range: 2-108). Near and far visual acuity, accommodation, convergent fusional range, stereopsis (Titmus and TNO test), maximal reading duration and subjective complaints (e.g. eye strain, headache) were evaluated. To separate improvements during treatment from spontaneous recovery of function or measurement artefacts we performed repeated measurements before treatment (baseline period) during a time span of 4-6 weeks. Follow-up measurements could be performed in 9 of 9 patients 10 months after cessation of treatment. RESULTS: No improvements were seen during the baseline period. 11 of 12 patients showed a significant recovery of fusional range during training which remained stable during the 10-month follow-up period. 10 of 11 patients showed significant improvements of local stereopsis (Titmus test) and 4 of 5 patients of global stereopsis (TNO test). All patients showed a significant increase of near visual acuity of about 10% (decimal visual acuity), improved reading ability and a reduction of subjective symptoms resulting from fusional deficiency, e.g. eye strain, headache. CONCLUSIONS: These results suggest a considerable potential for recovery of oculomotor and visual functions in brain damaged patients after training.

Accommodation, Ocular↗
PubMed1985

[Measurement of stereoscopic vision in 6-year-old preschool children].

Stereoacuity can be measured accurately in 6-year-old (pre-school age) children using a specially designed test. The values obtained, measured with stereo testers for long-range and close-range vision, do not differ significantly from those obtained in adults. Hence, it appears that the development of binocular vision must be terminated earlier than hitherto assumed. The limiting factor in stereo measurements at this age and with these methods is the degree of maturity of the children's mental and motor capabilities.

Child↗
PubMed1975

Recalibration by pairing: a process of perceptual learning.

When two cues which normally agree in determining perceived depth are experimentally paired so that they designate discrepant values for the depth dimension, an opportunity is created for the recalibration or re-evaluation of the cues. Experiments which show recalibration of the oculomotor cues and recalibration of binocular disparity as a result of pairing these cues with other discrepant cues are reviewed. The locus of change is related to the relative dominance of different cues and the contribution of allocation of attention in determining dominance is discussed. Implications of recalibration by pairing for understanding ontogenetic development are considered. It is suggested that some cues may acquire their effectiveness as a consequence of pairing during development.

Cues↗
PubMed1989

Measuring attention using induced motion.

Attention was measured by means of its effect upon induced motion. Perceived horizontal motion was induced in a vertically moving test spot by the physical horizontal motion of inducing objects. All stimuli were in a frontoparallel plane. The induced motion vectored with the physical motion to produce a clockwise or counterclockwise tilt in the apparent path of motion of the test spot. Either a single inducing object or two inducing objects moving in opposite directions were used. Twelve observers were instructed to attend to or to ignore the single inducing object while fixating the test object and, when the two opposing inducing objects were present, to attend to one inducing object while ignoring the other. Tracking of the test spot was visually monitored. The tilt of the path of apparent motion of the test spot was measured by tactile adjustment of a comparison rod. It was found that the measured tilt was substantially larger when the single inducing object was attended rather than ignored. For the two inducing objects, attending to one while ignoring the other clearly increased the effectiveness of the attended inducing object. The results are analyzed in terms of the distinction between voluntary and involuntary attention. The advantages of measuring attention by its effect on induced motion as compared with the use of a precueing procedure, and a hypothesis regarding the role of attention in modifying perceived spatial characteristics are discussed.

Adult↗
PubMed1990

Wallpaper illusion: cause of disorientation and falls on escalators.

The wallpaper illusion, first described over a century ago, can occur when a person with normal binocular vision views a pattern that is periodic in the horizontal meridian of the visual field. Escalator trends present such a pattern. Evidence is presented favoring the view that disorientation experienced by escalator riders is caused by this illusion. Possibly some of the estimated 60,000 escalator falls occurring in the United States each year are linked to it.

Accidental Falls↗
PubMed1991

The ceiling of the Church of St Ignatius and the perception of concave surfaces.

This research describes two hitherto unobserved phenomena in the frescoes of the seventeenth century architect and painter, Andrea Pozzo, painted on the vaulted ceiling of the central nave of the Church of St Ignatius in Rome. The present research also reports the results of two experimental studies on the problem of the perception of shapes projected on concave surfaces. A quantitative evaluation of the phenomena perceived from various points of observation is made by means of stimuli projected at various angles on a semicylindrical surface. The validity of the assumption of invariance, and in particular of the projective invariant called the cross-ratio, is discussed within the framework of ecological theories on perception.

Architecture↗
PubMed1992

Grouping based on phenomenal similarity of achromatic color.

It is widely acknowledged that a precondition for the perception of the world of objects and events is an early process of organization, and it has generally been assumed that such organization is based on the Gestalt laws of grouping. However, the stage at which such grouping occurs, whether early or late, is an empirical question. It is demonstrated in two experiments that grouping by similarity of neutral color is based not on similarity of absolute luminance at the level of the proximal stimulus, but on phenomenal similarity of lightness resulting from the achievement of lightness constancy. An alternative explanation of such grouping based on the equivalence of luminance ratios between elements and background is ruled out by appropriate control conditions.

Adult↗
PubMed1993

Apparent relative size and depth of moving objects.

The effects of the relative velocities of moving objects on their apparent relative size and depth were investigated with the aid of square patterns generated on a CRT display by a microcomputer. The observer matched the apparent sizes of squares, arranged in two or more rows that moved with different velocities, and made judgments of the apparent relative depth of the rows. In many conditions, squares moving more slowly were perceived as larger in size than those moving faster, regardless of the kind of depth responses, but in some conditions which contained strong depth cues the size responses seemed to be affected by perceived depth. The size-change effect of moving objects is discussed from the viewpoint of size-depth relationship.

Acceleration↗
PubMed1993

New depth to the Müller-Lyer illusion.

It is demonstrated that when the two halves of the Müller-Lyer illusion are shown separately to the two eyes this can result in a perception of the binocularly viewed shaft as slanted in depth. For short fin lengths, the magnitude of this slant can be predicted by the extent of the ordinary two-dimensional illusion. This result is discussed in relation to Julesz's claim that stereoscopic matching of the images in the two eyes must precede whatever process is responsible for the Müller-Lyer illusion (whereas the reported illusion seems to imply the reverse). The cyclopean Müller-Lyer demonstration on which Julesz's argument is based is reexamined. It is suggested that the matching of coarse-scale features in the images in the two eyes may help to explain both the cyclopean and the reported three-dimensional Müller-Lyer illusion.

Depth Perception↗
PubMed1993

Stereoscopic slant reversals: a new kind of 'induced' effect.

Data are presented from three experiments confirming an earlier finding that the stereoscopic slant perceived may be opposite to the geometrically predicted direction of slant (Gillam 1967). The stimulus for stereoscopic slant was created by imposing a disparity gradient on a frontal plane surface. Reversals are shown to occur readily for slants around a vertical axis but rarely for slant around a horizontal axis. Reversal frequency is greater for surfaces which have a regular pattern, providing good perspective information about slant. Cue conflict cannot explain reversals because adherence to perspective information predicts a perception of zero slant rather than reverse slant. A new explanation has been proposed attributing reversals to the ambiguity of horizontal disparity gradients and disambiguation of the disparity gradient by its relationship to the perspective gradient. It is shown that for any given disparity gradient there is a physical surface which would give rise to a slant reversed with respect to that normally predicted. Such a surface is eccentric in the field of view, with eccentricity given by the difference between the slants signalled by the disparity gradient and the perspective gradient. This explains why reversal responses to disparity gradients occur in the presence of perspective. It is proposed, on the basis of this analysis and the fact that reversals occur, that, like convergence and vertical disparity, perspective is a factor contributing to the correct scaling of disparity gradients in the horizontal meridian with respect to surface eccentricity.

Attention↗
PubMed1994

The natural moon illusion: a multifactor angular account.

It is argued that the failure to explain the celestial illusion results from conceptual confusion about perceived size and from disregard of the observational evidence relating to the natural moon illusion. The evidence shows that the illusion consists of a perceived angular size enlargement of horizon objects, by a factor of about 1.5-2.0 in diameter in comparison with elevated objects. Most measurements of the illusion have been made in terms of angular size, although in some proposed explanations an illusion of linear size is assumed. The magnitude of the illusion varies, particularly with the detail of the horizon scene. The illusion can be explained as the sum of several factors that affect perceived angular size: size contrast, vergence commands and eye or head position, aerial perspective, and colour. The relative contributions of these factors are assessed.

Color Perception↗
PubMed1995

Spatial-gradient limit on perception of multiple motion.

Motion is perceived whenever a subject is presented with an appropriate spatiotemporal visual pattern. Like many other visual tasks, motion perception involves both local and global processing, and thus might be subject to the well-known paradox that arises from the fact that local features and observations form the basis for global perception, but sometimes this global percept can not be easily derived from any single local observation, as is best exemplified by the aperture problem. Globally, dual (transparent) motion can be readily perceived. Spatial limits on the local ability to perceive multiple motion are sought. By using the framework of apparent motion, it is found that dual, orthogonally oriented motion can be perceived only when the dots that constitute the two motions are separated by some spatial limit. For short-range apparent motion, the limit is found to be comparable to D(max), and the visual system cannot perceive more than a single coherent motion in a local "patch" of radius D(max). It was also found that this spatial limit on local-motion perception is not constant, but depends linearly on the spatial organisation of the stimuli, and vanishes for stimuli having reverse contrast. The lower bound on the ability to perceive multiple motion is compared with some well-known bounds in stereopsis, and a cortical columnar architecture that might account for it is proposed.

Adult↗
PubMed1979

A developmental study of three-dimensional perception in Israeli children.

One hundred thirty-six 5- to 10-year-old Israeli male and female children were given three black and white photographs of a highway, a column of identical tanks, and a row of elephants, and were asked some questions on each one of the photographs in order to elicit responses of three-dimensional perception. The results showed a clear developmental pattern, quite similar to what has been found in other studies. It appears that the procedure used in the present study is an easier and probably more reliable way of assessing perspective responses than the original procedure of Piaget and Inhelder.

Child↗