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PubMed1990

New phenomena linking depth and luminance in stereoscopic motion.

A novel random-dot stereogram (RDS) was used to study stereoscopic motion. For this RDS stimulus, the direction of luminance motion and the direction of the moving cyclopean pattern can be independently controlled. The perceived cyclopean motion was examined under five different conditions, in which the cyclopean pattern was moving either up or down, the luminant dots were: (1) moving in the cyclopean direction; (2) moving opposite to the cyclopean direction; (3) moving orthogonal to the cyclopean direction, (4) stationary; or (5) dynamic (dots uncorrelated in successive frames). The study showed that luminance direction dominated cyclopean direction and that smooth and coherent cyclopean motion is seen only if luminance motion is present. The results suggest that stereoscopic motion is processed by interactions between separate binocular disparity units and luminance motion units, and not by a single binocular motion system, in which binocular units are tuned to both disparity and direction of motion.

Depth Perception↗
PubMed1997

Quantitative analysis of the accommodative convergence to accommodation ratio: linear and nonlinear static models.

Ogle and his colleagues proposed two measures of oculomotor linkage called the accommodative convergence to accommodation (AC/A) ratio. This ratio provided a clinically useful assessment of the drive of accommodation, or focusing system, on vergence, or binocular fixation system. The phoria method measured the relatively large deviation in eye alignment under the monocular condition, whereas the fixation disparity method measured the relatively small misalignment of the eyes under the binocular condition to obtain the AC/A ratio. Ogle et al. indicated that these two measures should be equal. However, experimental results showed a substantial difference between the AC/A ratios obtained by the two methods. To quantitatively assess the difference between the two methods, a linear static model was first evaluated. This model was based on an earlier successful model of the accommodation and vergence system. The linear-model solution showed that these two methods were equivalent and thus could not account for the differences found. Then, a nonlinear static model, containing the deadspace operators depth of field and Panum's fusional area (PFA), was evaluated. Since two solutions were possible for each deadspace operator, there were four basic solutions. However, there were two binocular-viewing paradigms. This resulted in four prism-viewing and four lens-viewing solutions. Finally, a difference was taken between the prism- and lens-viewing measures, giving a total combination of 16 solutions. Only four of these solutions were equal to that using the phoria method. Some of the other solution lines were widely separated, thus providing a range of possible data values across different solution lines. Calculations showed that the variation in AC/A ratio values for data across difference solution lines was comparable to that found experimentally. Thus, the deadspace operators in the nonlinear model were able to account for the discrepancy between the AC/A ratio determined by the phoria and fixation disparity methods.

Accommodation, Ocular↗
PubMed2005

Fast unambiguous stereo matching using reliability-based dynamic programming.

An efficient unambiguous stereo matching technique is presented in this paper. Our main contribution is to introduce a new reliability measure to dynamic programming approaches in general. For stereo vision application, the reliability of a proposed match on a scanline is defined as the cost difference between the globally best disparity assignment that includes the match and the globally best assignment that does not include the match. A reliability-based dynamic programming algorithm is derived accordingly, which can selectively assign disparities to pixels when the corresponding reliabilities exceed a given threshold. The experimental results show that the new approach can produce dense (> 70 percent of the unoccluded pixels) and reliable (error rate < 0.5 percent) matches efficiently (< 0.2 sec on a 2GHz P4) for the four Middlebury stereo data sets.

Algorithms↗
PubMed1998

Listening to migrant voices: focus groups on health issues in south Georgia.

This qualitative study utilized focus groups to invite Latino migrant farm workers to express ideas about their health and service needs. Four focus groups composed of Latino men and women were conducted on four different evenings in the same county. Three themes emerged: health care issues, living and working conditions, and social and community issues. Specific needs of the community were also identified by the participants. For the first time, migrant farm workers in Georgia had the opportunity to lend their own voice regarding their concerns and ideas about health and social conditions. The findings from this study are congruent with other studies and provide the basis for developing interventions to enhance the health of migrant farm workers. In addition, the findings have implications for community health nursing and the proposed Vision of 2010: Healthy People in Healthy Communities, whose goals include increased years of healthy life and the elimination of health disparities.

Adolescent↗
PubMed1978

The fixation disparity-heterophoria relationship.

If the heterophoria is the cause of a fixation disparity, then certain conditions can be experimentally observed. An experiment was performed and the conditions previously set forth as indicative of a cause-effect relationship between the heterophoria and fixation disparity were observed.

Adult↗
PubMed1995

Receptors, photoreception and brain perception. New insights.

Once photons have activated photosensitive cell receptors, a biochemical process mediated by G-proteins transforms the initial signal into nerve potentials. The generated impulses transmit the information through ganglion cells, after a complex interaction with other neurons by means of different neurotransmitters. Since visual function is processed in parallel, ganglion cells are divided into M-neurons which are in charge of capturing large objects, P-neurons capable of analyzing fine details and colors, and non-M, non-P neurons which are sensitive to changes in light intensity. Retina, bipolar and ganglion cells share circular receptive fields with an antagonistic surround whereas the lateral geniculate nucleus possesses rectangular receptive fields. Thus, when central cones are stimulated, ON-center cells depolarize, while OFF-center cells hyperpolarize. At the brain cortex, the magnocellular layers lead to orientation and achromatic perception, the parvocellular layers perform color vision in the blobs and achromatic contrast and orientation in the interblobs, and eventually, binocular perception is the result of multiple disparities phenomenon. On these bases, patients with agnosia for form and pattern or for depth and movement have been described. Likewise, color blindness is another disease that could be the result of photoreceptor dysfunctions or brain perception defects.

Animals↗
PubMedDate not supplied

[Stereoscopic perception. Probable intervention of pulvinar neurons in the cat (author's transl)].

With the aid of a programme of automatic analysis it has been possible to determine the visual fields of each eye in the case of binocular cells in the pulvinar, lateral-posterior and supageniculate nuclei. The visual properties determined by stimulation of one eye were often similar to those of the other eye. By an objective method of determination of the centre of activity of the receptive fields it was possible to measure disparities between large fields of neurons of these structures. These disparities are compatible with the intervention of these associative nuclei of the postero-lateral thalamus in the mechanisms in stereoscopic vision.

Animals↗
PubMed2006

Vision and oral health needs of individuals with intellectual disability.

Over the past 20 years, there has been an increased emphasis on health promotion, including prevention activities related to vision and oral health, for the general population, but not for individuals with intellectual disability (ID). This review explores what is known about the prevalence of vision problems and oral health conditions among individuals with ID, presents a rationale for the increased prevalence of these conditions in the context of service utilization, and examines the limitations of the available research. Available data reveal a wide range of prevalence estimates for vision problems and oral health conditions, but all suggest that these conditions are more prevalent among individuals with ID compared with the general population, and disparities exist in the receipt of preventive and early treatment for these conditions for individuals with ID. Recommendations for health improvement in these areas include better health planning and monitoring through standardized population-based data collection and reporting and increased emphasis on health promotion activities and early treatment in the healthcare system.

Adolescent↗
PubMed1991

The Charles F. Prentice Award Lecture 1990: specific tests and specific blindnesses: keys, locks, and parallel processing.

Classical color vision theory incorporates the concepts of hard-wired parallel independent processing and of hard-wired opponent-processing. These two powerful concepts can be applied more generally in visual psychophysics. The concept of parallel independent processing can help to understand two extremes of visual performance: disordered vision in patients and the extraordinary visual abilities of athletes and aviators. Three illustrations of this thesis are discussed. First, evidence for dissociations of spatial vision for low-contrast and high-contrast objects. Second, evidence that a binocular system for motion in depth runs in parallel with the classical disparity-driven binocular system for relative position in depth. Third, evidence that a visual system for motion-defined form parallels the well known system for contrast-defined form. However, in principle these two concepts have limited value because they do not incorporate the possibility that the functional organization of the visual pathway could be modified by descending task-dependent signals.

Awards and Prizes↗
PubMed1978

[Diplopia in monocular aphakia].

In monocular aphakia, diplopia results from disparities between the two retinal images in form, size, outline, luminous intensity and colour. If one wishes to give the best binocular vision possible to a monocular aphake, it is important to recognize the different factors which may give rise to diplopia.

Aniseikonia↗
PubMed2003

Computational model for neural representation of multiple disparities.

It has been known that the visual system can detect more than one disparity and/or motion direction at the same region in the image. These multiple (or transparent) surfaces can be perceived when, for example, we are looking scenes through a glass. However, many conventional models cannot deal with these multiple surfaces. The present paper investigates the neural encoding and decoding of multiple disparities with the binocular energy model, which is known as a biologically plausible model. Based on the analysis of the response of the energy model to multiple disparities, the present paper proposes a stereo model that can detect disparities of two overlapping surfaces.

Algorithms↗
PubMedDate not supplied

Direction repulsion in motion transparency.

A series of experiments investigated perceived direction of motion and depth segregation in motion transparency displays consisting of two planes of dots moving in different directions. Direction and depth judgments were obtained from human observers viewing these "bi-directional" animation sequences with and without explicit stereoscopic depth information. We found that (1) misperception of motion direction ("direction repulsion") occurs when two spatially intermingled directions of motion are within 60 deg of each other; (2) direction repulsion is minimal at cardinal directions; (3) perception of two directions of motion always results in separate motion planes segregated in depth; and (4) stereoscopic depth information has no effect on the magnitude of direction repulsion, but it does disambiguate the depth relations between motion directions. These results are developed within the context of a two-stage model of motion transparency. On this model, motion directions are registered within units subject to inhibitory interactions that cause direction repulsion, with the outputs of these units pooled within units selective for direction and disparity.

Adaptation, Ocular↗
PubMed1996

Alhazen's neglected discoveries of visual phenomena.

The first three books of the Book of Optics written by Alhazen in Cairo in the eleventh century were translated into English by A I Sabra in 1989. Book I deals with optics, the structure of the eye, image formation in the eye, and with the visual pathways. This book inspired all other books on optics from the thirteenth to the seventeenth century and formed the basis upon which Kepler solved the problem of image formation. However, Alhazen's work contained in Books II and III has been almost totally ignored. These two books contain an account of hundreds of observations and experiments carried out by Alhazen on a broad range of topics which are now studied under the heading of visual perception. He clearly enunciated many of the fundamental principles which are credited to scientists living in the last two hundred years, including a theory of unconscious inference; the law of equal innervation of the eye muscles; the principles of binocular direction; constancy of size, shape, and colour; induced visual motion; the vertical horopter; the fusional range of binocular disparity; and many others.

Egypt↗