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PubMed1978

Association of symptoms with measures of oculomotor deficiencies.

Phoria, vergence, and fixation-disparity were measured at near working distances for a nonclinical sample of 3rd-yr optometry students. A questionnaire divided the sample into 33 symptomatic and 44 asymptomatic subjects. Discriminant analysis was used to determine which clinical measures best predicted the group to which each subject belonged. Sheard's criterion was a good discriminator for exo deviations, and a variant of Percival's criterion was good for eso deviations. Fixation-disparity variables proved to be valuable diagnostically. The best fixation-disparity measures were the curve slope, curve type, and amount of fixation disparity.

Asthenopia↗
PubMed1986

Nonius horopter in projected viewing.

Nonius horopter measurements were made on three normal subjects using both physically displaced (real viewing) and stereogrammetrically displaced (projected viewing) test objects. Three subjects with ocular anomalies were tested using the projected viewing arrangement with and without 5% overall magnifier before the right eye, and seven complete measurements of the projected viewing horopter were made on a fourth subject with an ocular anomaly over the period of 1 month. These latter individual plots showed large irregularities that changed location from day to day. Plotting the mean and standard error of the means of these seven sets of data produced a smoothing out of the horopter locus. Plotting each individual horopter setting in the sequence of measurement and monitoring eye position indicated that all of the irregularities and regional horopter changes found are most likely introduced by changes in fixation disparity (vergence eye movements).

Depth Perception↗
PubMed2004

Performance data indicate summation for pictorial depth-cues in slanted surfaces.

Over recent years much has been learned about the way in which depth cues are combined (e.g. Landy et al.. 1995). The majority of this work has used subjective measures, a rating scale or a point of subjective equality, to deduce the relative contributions of different cues to perception. We have adopted a very different approach by using two interval forced-choice (21FC) performance measures and a signal processing framework. We performed summation experiments for depth cue increment thresholds between pairs of pictorial depth cues in displays depicting slanted planar surfaces made from arrays of circular 'contrast' elements. Summation was found to be ideal when size-gradient was paired with contrast-gradient for a wide range of depth-gradient magnitudes in the null stimulus. For a pairing of size-gradient and linear perspective, substantial summation (> 1.5 dB) was found only when the null stimulus had intermediate depth gradients; when flat or steeply inclined surfaces were depicted, summation was diminished or abolished. Summation was also abolished when one of the target cues was (i) not a depth cue, or (ii) added in conflict. We conclude that vision has a depth mechanism for the constructive combination of pictorial depth cues and suggest two generic models of summation to describe the results. Using similar psychophysical methods. Bradshaw and Rogers (1996) revealed a mechanism for the depth cues of motion parallax and binocular disparity. Whether this is the same or a different mechanism from the one reported here awaits elaboration.

Cues↗
PubMed2002

The perception of body orientation after neck-proprioceptive stimulation. Effects of time and of visual cueing.

Different sensory systems (e.g. proprioception and vision) have a combined influence on the perception of body orientation, but the timescale over which they can be integrated remains unknown. Here we examined how visual information and neck proprioception interact in perception of the "subjective straight ahead" (SSA), as a function of time since initial stimulation. In complete darkness, healthy subjects directed a laser spot to the point felt subjectively to be exactly straight ahead of the trunk. As previously observed, left neck muscle vibration led to a disparity between subjective perception and objective position of the body midline, with SSA misplaced to the left. We found that this displacement was sustained throughout 28 min of continuous proprioceptive stimulation, provided there was no visual input. Moreover, prolonged vibration of neck muscles leads to a continuing disparity between subjective and objective body orientation even after offset of the vibration; the longer the preceding vibration, the more persistent the illusory deviation of body orientation. To examine the role of vision, one group of subjects fixated a central visual target at the start of each block of continuous neck vibration, with SSA then measured at successive intervals in darkness. The illusory deviation of SSA was eliminated whenever visual input was provided, but returned as a linear function of time when visual information was eliminated. These results reveal: the persistent effects of neck proprioception on the SSA, both during and after vibration; the influence of vision; and integration between incoming proprioceptive information and working memory traces of visual information.

Adult↗
PubMed2005

Colour helps to solve the binocular matching problem.

The spatial differences between the two retinal images, called binocular disparities, can be used to recover the three-dimensional (3D) aspects of a scene. The computation of disparity depends upon the correct identification of corresponding features in the two images. Understanding what image features are used by the brain to solve this binocular matching problem is an important issue in research on stereoscopic vision. The role of colour in binocular vision is controversial and it has been argued that colour is ineffective in achieving binocular vision. In the current experiment subjects were required to indicate the amount of perceived depth. The stimulus consisted of an array of fronto-parallel bars uniformly distributed in a constant sized volume. We studied the perceived depth in those 3D stimuli by manipulating both colour (monochrome, trichrome) and luminance (congruent, incongruent). Our results demonstrate that the amount of perceived depth was influenced by colour, indicating that the visual system uses colour to achieve binocular matching. Physiological data have revealed cortical cells in macaque V2 that are tuned both to binocular disparity and to colour. We suggest that one of the functional roles of these cells may be to help solve the binocular matching problem.

Color↗
PubMed1997

A functional role for illusory colour spreading in the control of focused visual attention.

In cases of modal completion, illusory colour spreading fills in the surface of a subjectively completed shape. In amodal completion, shapes are likewise completed, but now behind a partial occluder, so that filling in of illusory colour to the completed region no longer arises. We consider the possible functional effects that illusory colour spreading may exert on later stages of vision, and argue that comparisons of modal with amodal completion may be particularly revealing in this regard. It is hypothesised that cueing the inducers of a modally completed object should attract attention to the entire object, including the completed region, owing to the colour spreading there. By contrast, changes to the inducers of a comparable amodally completed object should only attract attention to the inducing regions themselves. This prediction is supported by findings in two experiments with stereoscopic displays, with control conditions ruling out nonattentional accounts, or explanations in terms of stereo disparity alone rather than the presence versus absence of illusory colour. We argue that illusory colours get filled in at quite early stages during modal completion, precisely so that later stages of vision, such as focused attention, can then be driven by the completed regions in the same way as for uniform regions that are physically present in the image.

Color Perception↗
PubMed1986

Vergence adaptation: a review.

The present review aims to discuss the current researches on the ability of the vergence system to adjust to new information. A concomitant or non-concomitant binocular retinal disparity caused by a prism or an anisometropic prescription can be adapted to such that the induced phoria of fixation disparity reduces back to the original value. The features and mechanisms of this normal adaptation and also the response in subjects with abnormal binocular vision are discussed. The less extensive work on the adaptive ability of the accommodative vergence system is also reviewed.

Accommodation, Ocular↗
PubMed1980

On the depth of the cyclopean retina.

The maximum disparity which can elicit depth perception was measured in dynamic random-dot stereograms as a function of stimulus size and duration. Maximum disparity increased with size as a function of the square root of stimulus area, and depth could under optimal conditions be perceived up to several arc degrees of disparity, even for short (48 ms) durations of exposure. These data delineate the limiting disparity/depth characteristics of the cyclopean retina, and provide fresh evidence of the distinction between local and global disparity processing.

Animals↗
PubMed2003

Detecting disparity in two-dimensional patterns.

One can measure the disparities between two retinal images in several different ways. Experiments were conducted to identify the measure that is invariant at the threshold for detecting the disparity of two-dimensional patterns. The patterns used were stereo plaids, which permit a partial dissociation between the disparity of the pattern and the disparities of its one-dimensional components. For plaids with near-horizontal disparities, thresholds are limited by a disparity phase shift equal to the threshold phase shift for single gratings. For non-horizontal disparities, thresholds are elevated, yet are still phase-limited. In no disparity direction are thresholds for detecting disparity determined by the spatial extent of the plaids' disparity. Effects of the number and the orientation of components with task-relevant disparities indicate that plaid thresholds are limited by the disparity of the plaid's one-dimensional components. No evidence was found that these components form any higher-order pattern that can be used in detecting disparity. Oblique and near-vertical disparities generate elevated thresholds at a stage beyond component disparity detection. This second stage combines component disparities, which are ambiguous about depth, into pattern disparities capable of supporting veridical depth perception.

Humans↗
PubMed1993

Merging nursing departments. An experience.

In 1979, two of the largest private, not-for-profit hospitals in New York City merged to become one institution under the aegis of a single corporate administration. The integration of two large and disparate nursing departments, each with its own distinct identity and organizational structure, into what would become a unified department of nursing with a shared vision and goals was a complex task. The author, the nurse executive who oversaw this transition, describes the process 12 years after the merger.

Health Facility Merger↗
PubMed2006

Improving health care in the 21st century: focus on Medicaid.

This report contains information from the Health Policy Summit, held in conjunction with the Fifth Annual Primary Care Conference and the Tenth Annual HeLa Women's Health Conference. During the Summit's presentation, the Honorable Newt Gingrich offered key elements of his "Vision for a 21st Century Medicaid Solution." The vision focuses on developing a "21st Century Responsible Citizen Medicaid Act," which will provide improved health outcomes, decreased healthcare spending, and dramatically reduced health disparities.

Health Care Reform↗
PubMed1979

What prior uniocular processing is necessary for stereopsis?

In order to induce stereoscopic depth, retinal images in the right and left eyes must differ. Our experiments demonstrate that these uniocular differences for simple three-line configurations at stereo-threshold cannot usually be distinguished one from the other. We confirm that depth values are associated with individual features by virtue of their disparity, rather than by a comparison of their image separations in the two eyes. In ordinary stereoacuity patterns, no prior identification of monocular relationships is needed to produce discriminable depth differences. For certain patterns, disparity of the positions of the averages of the targets' internal light distributions in the two eyes can substitute for disparity of pattern contours in stereoscopic depth discrimination.

Depth Perception↗
PubMed1979

Noonan's syndrome. IQ and specific disabilities.

The IQ of eight male patients with Noonan's syndrome, aged 13 to 26 years, ranged from 64 to 127, with a median of 102. The full IQ masked the possible presence of specific verbal or praxic (visual-constructional) disability. There was no verbal/praxic disparity in three cases; there was substantial verbal disability in one case; and there was major praxic disability in four cases, three unrelated to vision and one accounted for by severe visual impairment. Ostensible general mental retardation in Noonan's syndrome should always be further evaluated for specific disability. Academic placement should then be arranged accordingly.

Adolescent↗
PubMed2003

Auditory influences on visual temporal rate perception.

Visual stimuli are known to influence the perception of auditory stimuli in spatial tasks, giving rise to the ventriloquism effect. These influences can persist in the absence of visual input following a period of exposure to spatially disparate auditory and visual stimuli, a phenomenon termed the ventriloquism aftereffect. It has been speculated that the visual dominance over audition in spatial tasks is due to the superior spatial acuity of vision compared with audition. If that is the case, then the auditory system should dominate visual perception in a manner analogous to the ventriloquism effect and aftereffect if one uses a task in which the auditory system has superior acuity. To test this prediction, the interactions of visual and auditory stimuli were measured in a temporally based task in normal human subjects. The results show that the auditory system has a pronounced influence on visual temporal rate perception. This influence was independent of the spatial location, spectral bandwidth, and intensity of the auditory stimulus. The influence was, however, strongly dependent on the disparity in temporal rate between the two stimulus modalities. Further, aftereffects were observed following approximately 20 min of exposure to temporally disparate auditory and visual stimuli. These results show that the auditory system can strongly influence visual perception and are consistent with the idea that bimodal sensory conflicts are dominated by the sensory system with the greater acuity for the stimulus parameter being discriminated.

Acoustic Stimulation↗
PubMed1989

[Comparison of the Kolling distance vision stereo-test with current stereo-test procedures].

A new type of stereotest for distant vision (after Kolling) is compared with established stereotests for distant (different types of Zeiss Polatest) and near vision (Titmus, TNO, Lang tests) in a total of 203 patients. The Kolling test is based on the three-rod method in accordance with Helmholtz. The apparatus does not require separation of the visual input of the two eyes. This new stereotest is practice-oriented, quick, easy to understand and gives reliable and reproducible results. The test cannot be completed successfully with monocular viewing, if the head is fixed. The results show a good correspondence between the Kolling test and the Zeiss Polatest using disparate outlined figures. The Zeiss Polatest using random-dot patterns turned out to have the strictest criteria for this purpose of all stereotests. Interestingly enough, subjects performed much better in stereotests for near vision (Titmus, TNO tests) than in those for distant vision (Kolling test, different types of Zeiss Polatest). The widespread use of stereotests of near vision in driving tests is therefore problematic.

Adolescent↗
PubMed1980

Meridional size disparity as a function of compressed inferior visual space: a case in point.

This case report describes a very unusual form of aniseikonia which was eventually documented to be variable within the total field of vision and limited to vertical space perception. Initially the condition could be partially relieved by monocular occlusion, visual training procedure, and the use of isoikonic lenses. Ultimately, the greatest improvement was produced by the introduction of prismatic properties to the lenses which directly addressed the patient's problem of meridional space perception.

Aniseikonia↗
PubMed1995

Lateral geniculate lamination and the corticogeniculate projection: a potential role in binocular vision in the quadrants.

Students of vision have long speculated about the functions of the distinct lamination of the lateral geniculate nucleus and the massive return projection from visual cortex to this thalamic structure. This paper proposes that these features of the visual system reflect, in part at least, its solution to a geometric problem inherent in binocular vision. Points in the visual quadrants are imaged on geometrically non-corresponding retinal points. Two such retinal loci, optically conjugate with a given visual point at one fixation distance or angle, will correspond to no single visual point at other fixation distances or angles. This raises potential problems for visual cortical neurons sensitive to a narrow range of binocular disparities. If these neurons are to function optimally at a variety of fixation distances and angles, their disparity tuning must be variable. It is suggested here that such dynamic disparity tuning is effected by the corticogeniculate projection acting on the segregated ocular representations in the geniculate laminae.

Animals↗