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PubMed1996

A general model for the perception of space and motion.

The perception of space and motion involves successive transformations of signals with respect to different reference systems. The visual input is coded in terms of retinal coordinates. The retinocentric values from each eye require to be unified, and to be combined with signals for eye position and movement. This egocentric reference provides a signal for the angular size, motion, or orientation of the stimulus with respect to the observer. The egocentric signals are transformed to a coordinate system that is three-dimensional-the geocentric frame of reference. Further transformations can occur at earlier levels owing to patterncentric interactions within the visual field. When the geocentric signal corresponds to the physical dimensions of space and motion, this is referred to as perceptual constancy.

Acceleration↗
PubMed1996

Interactions of monocular and cyclopean components and the role of depth in the Ebbinghaus illusion.

A study of size interactions of objects in three-dimensional space is reported. The canonical form of the Ebbinghaus illusion-test circles surrounded by large or small inducers-was used. Both monocularly visible (M) and purely cyclopean (C) objects were displayed stereoscopically to isolate the monocular and cyclopean components of the illusion. The results of two experiments indicate that: (i) depth plays a significant role when the test circles are cyclopean, but not when they are monocularly visible; and (ii) the size of C objects is affected equally by C and M inducers, but the size of M objects is affected much more strongly by M than by C inducers. In conclusion, possible explanations are offered for the main trends in the data, the most interesting of which is that cyclopean tests seem to be interacting only with the cyclopean component of monocularly visible inducers.

Adult↗
PubMed1996

Patterns that impair discrimination of line orientation in human vision.

The threshold for detecting a change in orientation away from the vertical of a briefly presented foveal line target is raised when there are immediately following visual presentations. This masking effect was examined by measuring the capacity of a variety of patterns to act as masks. When patterns were made of exactly the same number of light pixels, masking was least when they formed random dots and progressively became stronger as they formed lines of decreasing curvature from full circles to straight lines. The longer the lines, the stronger the masking. Threshold elevation was highest when the masking pattern was spatially superimposed on the line and was lessened when a large surround area was included, but there was still considerable masking when the interfering patterns were confined to the surround. By placing masks and test lines in different eyes, or by giving them opposite contrast polarity, almost complete interocular and interpolarity transfer was demonstrated. Relating these results to anatomical and electrophysiological findings about neurons in the primary visual cortex leads to the conclusion that the masking effects could have their substrates in interaction between cells in VI.

Humans↗
PubMed1997

Interactions of spatial frequency and unequal monocular contrasts in stereopsis.

Increasing the contrast of just one eye's image degrades stereothresholds; this phenomenon is referred to as the stereo contrast paradox. In experiment one, this paradox was found to be absent in dynamic random-element stereograms; thresholds were simply limited by the lower of the two eyes' contrasts. In experiment two, in which narrowband Gabor targets were used, the paradox was found to be strongest at relatively low spatial frequencies (1 cycle deg-1). As spatial frequency was increased, the paradox gradually disappeared. At relatively high spatial frequencies (5 cycles deg-1), thresholds were generally limited by the lower of the two eyes' contrasts, as was found for the dynamic noise targets. These results demonstrate the interactions of spatial frequency and contrast in binocular image combination and yield clues as to the different roles which high and low spatial frequencies may play in stereopsis.

Contrast Sensitivity↗
PubMed2000

On binocular alternation.

Diaz-Caneja (1928) made some prescient observations about binocular rivalry. Being in French, however, his paper remained largely unknown to the broader research community. His findings are similar to those reported very recently by contemporary researchers who had independently observed similar phenomena. Using concentric circles and parallel lines as stimuli, Diaz-Caneja presented half of each form to opposite eyes to provoke binocular rivalry. He observed periods in the ensuing binocular alternations in which rivalry occurred between the good Gestalt forms, despite the fact that they were distributed between the eyes. He proposed that each half of a good form generates synchronised oscillations in the visual system, and that this synchronisation enables the dichoptically viewed halves of the one form to be perceived as a whole.

Animals↗
PubMed2002

The pursuit of Leonardo's constraint.

Leonardo da Vinci (1452-1519) identified two stimulus situations that cannot be painted faithfully on a canvas: (a) when two objects are located in the same direction with respect to the painter's head, and (b) when parts of a surface are visible to one eye, but occluded from the other eye. He analysed these situations in terms of rays being emitted from the two eyes and, aside from the origin of the rays, the projective geometry he used was correct. His analyses showed that what can be seen from two vantage points cannot be represented on a canvas, because a 'correct' painting must be created from a single 'station point'. He was struck by the consequence of this fact that the depth seen on a canvas cannot match that of viewing the scene with two eyes. Subsequent visual scientists focused on Leonardo's observation about the lack of vivid depth in a picture. We argue that a complete understanding of what we see in the two stimulus situations requires consideration of visual direction in addition to visual depth. More specifically, we argue that the visual directions of the two objects, (a) above, and the visual direction of the monocular areas, (b) above, are dependent upon the constraint that two opaque objects cannot be represented in the same direction. Demonstrations that readers can perform, and that support this argument, are provided on the Perception website at http://www.perceptionweb.com/perc0102/ono.html.

Depth Perception↗
PubMed2000

The temporal course of suppression during binocular rivalry.

Orthogonally oriented sinusoidal luminance gratings were dichoptically presented to the observers' left and right eyes. During the subsequent binocular rivalry, a small target was briefly presented (4AFC) to probe the strength of interocular suppression at various temporal latencies. Both stationary and moving rivalrous patterns were investigated. The purpose of experiment 1 was to compare the temporal characteristics of stationary and motion rivalry (0 and 1.2 deg s-1), while that of experiment 2 was to examine rivalry suppression for higher speeds (2 and 4 deg s-1). In all cases, it was found that the strength of suppression remained essentially constant throughout a single phase of binocular rivalry. The results of the investigation also revealed that moving rivalrous patterns lead to greater magnitudes of interocular suppression than static patterns. Despite these differences in the strength of suppression, the results of both experiments show that the temporal characteristics of motion and static rivalry are essentially identical.

Female↗
PubMed2003

A common oscillator for perceptual rivalries?

Perceptual rivalry is an oscillation of conscious experience that takes place despite univarying. if ambiguous, sensory input. Much current interest is focused on the controversy over the neural site of binocular rivalry, a variety of perceptual rivalry for which a number of different cortical regions have been implicated. Debate continues over the relative role of higher levels of processing compared with primary visual cortex and the suggestion that different forms of rivalry involve different cortical areas. Here we show that the temporal pattern of disappearance and reappearance in motion-induced blindness (MIB) (Bonneh et al, 2001 Nature 411 798-801) is highly correlated with the pattern of oscillation reported during binocular rivalry in the same individual. This correlation holds over a wide range of inter-individual variation. Temporal similarity in the two phenomena was strikingly confirmed by the effects of the hallucinogen LSD, which produced the same, extraordinary, pattern of increased rhythmicity in both kinds of perceptual oscillation. Furthermore. MIB demonstrates the two properties previously considered characteristic of binocular rivalry. Namely the distribution of dominance periods can be approximated by a gamma distribution and, in line with Levelt's second proposition of binocular rivalry, predominance of one perceptual phase can be increased through a reduction in the predominance time of the opposing phase. We conclude that (i) MIB is a form of perceptual rivalry, and (ii) there may be a common oscillator responsible for timing aspects of all forms of perceptual rivalry.

Adult↗
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↗
PubMed2006

Plaid motion rivalry: correlates with binocular rivalry and positive mood state.

Recently Hupé and Rubin (2003, Vision Research 43 531- 548) re-introduced the plaid as a form of perceptual rivalry by using two sets of drifting gratings behind a circular aperture to produce quasi-regular perceptual alternations between a coherent moving plaid of diamond-shaped intersections and the two sets of component 'sliding' gratings. We call this phenomenon plaid motion rivalry (PMR), and have compared its temporal dynamics with those of binocular rivalry in a sample of subjects covering a wide range of perceptual alternation rates. In support of the proposal that all rivalries may be mediated by a common switching mechanism, we found a high correlation between alternation rates induced by PMR and binocular rivalry. In keeping with a link discovered between the phase of rivalry and mood, we also found a link between PMR and an individual's mood state that is consistent with suggestions that each opposing phase of rivalry is associated with one or the other hemisphere, with the 'diamonds' phase of PMR linked with the 'positive' left hemisphere.

Adolescent↗
PubMed2006

Binocular rivalry and surface-boundary processing.

Theoretical and empirical studies show that the visual system relies on boundary contours and surface features (e.g. textures) to represent 3-D surfaces. When the surface to be represented has little texture information, or has a periodic texture pattern (grating), the boundary contour information assumes a larger weight in representing the surface. Adopting the premise that the mechanisms of 3-D surface representation also determine binocular rivalry perception, the current paper focuses on whether boundary contours have a similar role in binocular rivalry. In experiment 1, we tested the prediction that the visual system prefers selecting an image/figure defined by boundary contours for rivalry dominance. We designed a binocular rivalry stimulus wherein one half-image has a boundary contour defined by a grating disk on a background with an orthogonal grating orientation. The other half-image consists solely of the (same orientation) grating background without the grating disk, ie no boundary contour. Confirming our prediction, the predominance for the half-image with the grating disk is approximately 90%, despite the fact that the grating disk corresponds to an area with orthogonal grating in the fellow eye. The advantage of the grating disk is dramatically reduced to about 50% predominance when a boundary contour is added to the background-only half-image at the location corresponding to the grating disk. We attribute this reduced advantage to the formation of a corresponding binocular boundary contour. In experiment 2 the grating background was substituted by a random-dot background in a similar stimulus design. We found that the perceptual salience of the corresponding binocular boundary contours extracted by the interocular matching process is an important factor in determining the dynamics of binocular rivalry. Experiment 3 showed that vertical lines with uneven thickness and spacing as the background reduce the contribution of the monocular boundary contour of the grating disk in binocular rivalry, possibly through the formation of binocular boundary contours between the local edges (vertical components) of the vertical lines and the corresponding grating disk.

Contrast Sensitivity↗
PubMed2006

A gain-control theory of binocular combination.

In binocular combination, light images on the two retinas are combined to form a single "cyclopean" perceptual image, in contrast to binocular rivalry which occurs when the two eyes have incompatible ("rivalrous") inputs and only one eye;s stimulus is perceived. We propose a computational theory for binocular combination with two basic principles of interaction: in every spatial neighborhood, each eye (i) exerts gain control on the other eye's signal in proportion to the contrast energy of its own input and (ii) additionally exerts gain control on the other eye's gain control. For stimuli of ordinary contrast, when either eye is stimulated alone, the predicted cyclopean image is the same as when both eyes are stimulated equally, coinciding with an easily observed property of natural vision. The gain-control theory is contrast dependent: Very low-contrast stimuli to the left- and right-eye add linearly to form the predicted cyclopean image. The intrinsic nonlinearity manifests itself only as contrast increases. To test the theory more precisely, a horizontal sine wave grating of 0.68 cycles per degree is presented to each eye. The gratings differ in contrast and phase. The predicted (and perceived) cyclopean grating also is a sine wave; its apparent phase indicates the relative contribution of the two eyes to the cyclopean image. For 48 measured combinations of phase and contrast, the theory with only one estimated parameter accounts for 95% of the variance of the data. Therefore, a simple, robust, physiologically plausible gain-control theory accurately describes an early stage of binocular combination.

Contrast Sensitivity↗
PubMed2001

Uncorrected binocular distance visual impairment in U.S. Hispanic children and adolescents.

PURPOSE: To assess and compare uncorrected binocular distance visual impairment rates in U.S. Hispanic children and adolescents. METHODS: Data from the Hispanic Health and Nutrition Examination Survey, 1982-1984, were analyzed for 6-19 year-old Cuban-Americans (n = 317), Mexican-Americans (n = 2519), and Puerto Ricans (n = 988). Visual acuity was assessed using Sloan Letters or Landolt Rings. RESULTS: Prevalence rates of uncorrected binocular distance visual impairment (20/30 or worse) were 15.5%, 14.9%, and 23.6% for Cuban-Americans, Mexican-Americans, and Puerto Ricans, respectively. After adjusting for age and gender, the differences between Puerto Ricans and both Cuban-Americans and Mexican-Americans were significant (p < 0.05). Children 6-12 years of age had lower visual impairment rates than 13-19 year-old adolescents. Girls had higher age-adjusted visual impairment rates than boys; these gender differences were statistically significant among Mexican-Americans (OR = 1.6, 95% CI = 1.1, 2.2) and Puerto Ricans (OR = 1.7, 95% CI = 1.2, 2.4). CONCLUSIONS: Among Hispanics, Puerto Rican children and adolescents have the highest prevalence rate of uncorrected binocular distance visual impairment; older age and female gender are associated with higher rates of uncorrected visual impairment.

Adolescent↗
PubMed2003

The plasticity of vertical motor and sensory fusion in normal subjects.

PURPOSE: It is generally agreed that vertical prism bar training can increase vertical fusion amplitude. However, little is known as to whether the increased vertical fusion amplitude following vergence exercise is due to improvement of the sensory or the motor system or both. The main aim of the present study was to determine the effect of vertical prism bar training on the motor and sensory components of vertical fusion. METHODS: Fifty normal subjects between 17 and 25 years of age were given vertical prism bar training to improve their vertical fusion amplitude. Vertical vergence eye movements were recorded using an infrared reflectance eye tracker system. The sensory component was assessed using a Sheedy disparometer. RESULTS: The findings of the present study showed that the average increase in vertical motor fusion was approximately 30% following vertical prism bar training. The maximum magnitude of VFD remained unchanged in the majority (73%) of subjects. CONCLUSIONS: The increase in the vertical fusion amplitude following vertical prism bar training is largely due to improvements in the vertical motor fusion. The prism training has little effect on the sensory component.

Adolescent↗
PubMed2001

Associated phoria and the measuring and correcting methodology after H.-J. Haase (MKH).

The test charts included in the Polatest, designed by H.-J. Haase and manufactured by Zeiss, are used in Germany, Switzerland and Scandinavia for prism correction of 'associated phoria.' From clinical experience with the Polatest Haase developed a motor and sensory theory of the different stages of decompensation of 'associated phoria ' and a strategy for its prismatic correction - the MKH (Measuring and Correcting Methodology after H.-J. Haase). The theory challenges many accepted ideas about the plasticity of the visual system and the use of prisms in the treatment of sensory abnormalities. This article, the first full description in English, describes and critically discusses the MKH.

Accommodation, Ocular↗
PubMed1996

Stereopsis with normal and reversed binocular parallax using a head mounted display in normal and strabismic subjects.

A virtual reality system using a head mounted display (HMD) was constructed for the purpose of finding out how human beings perceive the three-dimensional world. Four ophthalmologically normal subjects and 4 strabismic patients (2 with exotropia, 2 with esotropia) were examined. They wore the HMD and viewed some familiar objects (e.g. human face) and an unfamiliar object (e.g. tangled ropes) under normal parallax, reversed parallax, and monocular conditions. They also attempted the ring and hook test under each condition. They recognized the normal familiar objects under each condition, but some normal subjects were confused when they perceived unfamiliar objects. The normal subjects barely passed the ring and book test under the reversed parallax condition. The results of the strabismic subjects showed change under each condition. Stereoptic ability in normal and strabismic patients were considered based on the above. Also considered were some stereoptic keys, binocular parallax, monocular stereoptic keys such as shadows, shades, texture, etc., the near reflex and the fact that the objects were familiar. It was found that the strabismic patients used monocular stereoptic keys more than normal people to supplement their lack of binocular parallax perception.

Adult↗
PubMed1996

Evaluation of stereoscopic picture quality with CFF.

The method of binocular stereoscopic imaging has attracted attention as a simple and technically feasible means of three-dimensional (3-D) display. It has been said, however, that the binocular picture system is more fatiguing to view than a conventional two-dimensional picture, much as the current television picture. The main objective of this paper is to evaluate quantitatively fatigue caused by binocular stereoscopic picture viewing, to clarify the basic characteristics of this type of picture. Various measurement methods of fatigue have been proposed, and that using the critical flicker frequency (CFF) has found wide use in measurement of mental fatigue and is easy to make. Actual measurement in this study used the CFF value obtained in a descending series of the method of limits, normalized to the value at the start of measurement for each observer, and the CFFs of all observers then averaged. It was found that the measurements produced stable and highly accurate results. CFFs of the observers of a current television picture and a binocular stereoscopic television picture were measured. It was found that the conventional television did not cause a statistically significant decrease in CFF--even over 1 h of viewing--but that the stereoscopic television did cause a significant CFF decrease within 30 min. It was also found that the CFF decreases are related to a subjective feeling of fatigue. From these results, it was concluded that CFF is an effective measure for objectively measuring the fatigue of television observers, including observers of binocular stereoscopic television. Also, the binocular stereoscopic television produced higher fatigue in observers than did the conventional television picture, but it was found that with respect to CFF viewing of around 30 min was allowable.

Accommodation, Ocular↗