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PubMed1994

Single-track effects and new directions in GCR risk assessment.

Light flashes in the eye as recorded by astronauts on missions outside the geomagnetosphere are presumably caused by single particle traversals of galactic cosmic rays traversing the retina. Although these flashes are not considered to have deleterious short- or long-term effects on vision, they are testimony that the body can detect single particle traversals. The frequencies of the flashes implicate ions in the charge range of 6 to 8 (i.e., carbon and/or oxygen ions). Other particles with higher charge and causing more ionization are present at lower frequencies. The possibility of the importance of such single-track effects in radiation carcinogenesis and other late effects suggest that a risk assessment system based on particle fluence rather than absorbed dose might be useful for assessing risk on long-term space missions. Such a system based on the concept of a risk cross section is described. Human cancer risk cross sections obtained from recently compiled A-bomb survival data are presented, and problems involving the determination of the LET-dependence of such cross sections are discussed.

Breast Neoplasms↗

PubMed1999

The influence of large scanning eye movements on stereoscopic slant estimation of large surfaces.

The results of several experiments demonstrate that the estimated magnitude of perceived slant of large stereoscopic surfaces increases with the duration of the presentation. In these experiments, subjects were free to make eye movements. A possible explanation for the increase is that the visual system needs to scan the stimulus with eye movements (which take time) before it can make a reliable estimate of slant. We investigated the influence of large scanning eye movements on stereoscopic slant estimation of large surfaces. Six subjects estimated the magnitude of slant about the vertical or horizontal axis induced by large-field stereograms of which one half-image was transformed by horizontal scale, horizontal shear, vertical scale, vertical shear, divergence or rotation relative to the other half-image. The experiment was blocked in three sessions. Each session was devoted to one of the following fixation strategies: central fixation, peripheral (20 deg) fixation and active scanning of the stimulus. The presentation duration in each of the sessions was 0.5, 2 or 8 s. Estimations were done with and without a visual reference. The magnitudes of estimated slant and the perceptual biases were not significantly influenced by the three fixation strategies. Thus, our results provide no support for the hypothesis that the time used for the execution of large scanning eye movements explains the build-up of estimated slant with the duration of the stimulus presentation.

Anisotropy↗

PubMed2005

Localization of the plane of regard in space.

When we fixate an object in space, the rotation centers of the eyes, together with the object, define a plane of regard. People perceive the elevation of objects relative to this plane accurately, irrespective of eye or head orientation (Poljac et al. (2004) Vision Res, in press). Yet, to create a correct representation of objects in space, the orientation of the plane of regard in space is required. Subjects pointed along an eccentric vertical line on a touch screen to the location where their plane of regard intersected the touch screen positioned on their right. The distance of the vertical line to the subject's eyes varied from 10 to 40 cm. Subjects were sitting upright and fixating one of the nine randomly presented directions ranging from 20 degrees left and down to 20 degrees right and up relative to their straight ahead. The eccentricity of fixations relative to the pointing location varied by up to 40 degrees . Subjects underestimated the elevation of their plane of regard (on average by 3.69 cm, SD=1.44 cm), regardless of the fixation direction or pointing distance. However, when the targets were shown on a display mounted in a table, to provide support of the subject's hand throughout the trial, subjects pointed accurately (average error 0.3 cm, SD=0.8 cm). In addition, head tilt 20 degrees to the left or right did not cause any change in accuracy. The bias observed in the first task could be caused by maintained tonus in arm muscles when the arm is raised, that might interfere with the transformation from visual to motor signals needed to perform the pointing movement. We conclude that the plane of regard is correctly localized in space. This may be a good starting point for representing objects in head-centric coordinates.

Arm↗

PubMed2002

Size scaling: retinal or environmental frame of reference?

Previous studies have reported that when subjects are presented with two forms in a same-different task, their reaction times increase with the size ratio. This suggests a "mental scaling" transformation analogous to the "mental rotation" used to compensate for differently oriented forms in similar tasks. However, since the stimuli were presented in isolation, retinal and environmental size ratios were confounded. The present study varied both retinal and environmental size ratios in a same-different simultaneous matching task. In one experiment, random forms were placed at different distances along a textured hallway. A second experiment varied the monocular size information: In one condition the forms were displayed in a textured hallway; a second condition added cast shadows; and a third condition displayed the forms against a frontal wall of indeterminate distance. The results suggest that environmental size is determined prior to mental scaling and form matching.

Adult↗

PubMed1984

The effects of caffeine on near point plus acceptance.

Forty-two university students participated in a study of reading with +0.50 sphere or yokes prism base down for overconvergence and base up for underconvergence. Sixty-four percent of the group improved with a mean of +10.79 wpm. The level of coffee consumption of each student was recorded. A negative correlation existed between the intake of caffeine and reading improvement, r = -.81, p less than .001. Two students reduced their coffee consumption and transformed their loss in words per minute to a significant gain. A double-blind protocol was used in this study. A placebo lens (plano) controlled for subject and investigator bias. The relationship between caffeine and accommodation was investigated by means of a monocular test through a +4.D sphere. The location of the blur point was indicative of the state of tonicity of the ciliary system. Pre- and post-tests of the blur point for 14 subjects who were tested before and after consuming 150 mg of caffeine showed a significant change. The experimental group showed an increase of -0.52D while the control group showed a change of +0.36D. r = .781, p less than .01.

Accommodation, Ocular↗

PubMed2004

Analysis of the optical quality of intraocular lenses.

PURPOSE: To evaluate the optical quality of different intraocular lenses (IOLs). METHODS: An optical test bench and suitable software were used to assist in analysis of the optical Fourier transform (OFT) of a test image and to determine the quality of the lens in terms of spatial frequency response. The OFT was automatically converted, by means of an optical-electronic calibration procedure, into a modulation transfer function (MTF) for each lens. The passband value calculated by computer analysis of the MTF is an objective index of the lens quality. Three randomly acquired samples of 24 different models of foldable IOLs were compared. Statistical analysis was performed with two-way and one-way ANOVA for repeated measurements and with the Ryan-Einot-Gabriel-Welsch multiple F test. RESULTS: The method was demonstrated to be precise and accurate. A large range of passband values was found. Statistically significant differences between the mean passband values for different lenses were found. The lowest passband value (125.60 line pairs [lp]/mm) was measured for the IOL (Lenstec LH3000; Lenstec, Inc., St. Petersburg, FL) and the highest (191.48 lp/mm) for the Acrysof SA30AL (Alcon, Fort Worth, TX). CONCLUSIONS: Different IOLs can transmit different spectra of spatial frequencies. The best frequency response was provided by acrylic IOLs, particularly those with an asymmetrically biconvex profile. This could be due to a reduction of optical degradation provided by this type of profile. A lens with a higher frequency response should determine a better quality of vision once implanted and the frequency response should therefore be considered when choosing the intraocular lens model.

Fourier Analysis↗

PubMed1997

Efficiency of the Ishihara test for identifying red-green colour deficiency.

The Ishihara test is the most widely used screening test for red-green colour deficiency. Results obtained by 401 people with red-green colour deficiency show that the combined sensitivity of the Transformation and Vanishing plates of the 38 plate Edition of the Ishihara plates is 95.5% on eight errors, 97.5% on six errors and 99.0% on three errors. The Hidden digit designs only identified approximately 50% of colour-deficient subjects. The protan/deutan classification plates were found to be more effective for deutans than for protans. No classification was obtained for 18% of protanopes and 3% of deuteranopes who saw neither figure on classification plates; 40% of protanomalous trichromats and 37.5% of deuteranomalous trichromats saw both classification figures and were classified on the relative luminance (clarity) of these figures. The specificity of the Ishihara test was determined in a previous study (Birch and McKeever, 1993) and the results combined with the present data to obtain the overall efficiency of the Ishihara plates for a representative cross section of colour-deficient subjects.

Adult↗

PubMed2000

A moment in time: AIDS and business.

Business has transformed the planet. But this gives it new responsibilities. People now expect business leaders to lead--and not just respond when things go wrong. HIV/AIDS is a global problem, with over 16.3 million people now thought to have died of the disease (Global Summary of HIV/AIDS Epidemic, UNAIDS, December 1999). Without action now, the pandemic will worsen, health services will come under relentless pressure and the number of people dying will increase exponentially. So why should business sit up and take notice? First: money. AIDS is slowly strangling many businesses and economies--and in a global market, everyone eventually suffers. Without profit, there is no business--so the business community needs to act to protect its bottom line. Second: people. Over 80% of those dying are in their 20s, 30s, and 40s. Businesses are losing workers and customers, and human networks that have taken decades to build. Third: imagination. Business is inventive, creative and fast-moving. It has the opportunity to use these strengths for the benefit of the wider community. It's time to pit business ideas (and some money, too) against the threat of AIDS. The course of the AIDS epidemic is not inevitable. The world's businesses have the skills and intensity to make a measurable difference, especially if they find public sector and NGO partners with whom they share a vision. A focused, coordinated, results-driven effort will hit AIDS hard. The HIV virus moves fast (and is mutating all the time). Business has the opportunity to make a difference. It must grasp this opportunity. And grasp if fast.

Commerce↗

PubMed1989

C. G. Jung and the shaman's vision.

Implications for Modern Analysis and Psychotherapy. After this rather wide-ranging journey reviewing the shamanic archetype with Jung as its centre, we come back to the question of what all this means for the present age. We are now into the second generation as followers of Jung in terms of the movement that has developed bearing his name. It is clear that the original founder, himself, performed the functions of a primitive shaman by the influence he has exerted on a culture and its power to deal with the elements of healing and curing. He has fused science and religion, or the rational and the irrational or mystical, in a remarkable synthesis. However, there is now much questioning in Jungian circles, as the initial light and power emanating from his personality are on the wane and as those who knew him are beginning to pass on, as to what is the meaning of the movement he represented. What we see emerging are the development of different approaches to treatment and to the healing process. At present, it could be said that there are eclectic or modern Jungians who function basically through dreams, treat relationship in a symbolic way and practise the paradigm of teacher and pupil. There are the priestly Jungians who might be considered 'classical' Jungians who have almost ritualistically tried to recreate what he represented, even bringing in the Swiss cultural background. They evoke the numinous and archetypal in the healing process much as priests do. There are the medical Jungians who have fused psychoanalysis with other traditions, such as Klein, Winnicott, Bion, Langs, Kohut and others, who express Jung and the healing process in technical, scientific terms. There are, finally, those few who might be called the 'true Jungians', who differ from other Jungians inasmuch as they, like Jung, function as shamans in the therapeutic process dealing directly with the patient's illness in order to produce a transformational healing experience. The great difficulty is that there are few analysts who can be shamans and work as Jung did. Shamanism, as the literature reveals, is a dangerous occupation and few can survive it for a long period of time, hence the natural tendency is to function in one of the other three larger categories and cross integrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Dissociative Disorders↗

PubMed2001

Nonlinear and extra-classical receptive field properties and the statistics of natural scenes.

The neural mechanisms of early vision can be explained in terms of an information-theoretic optimization of the neural processing with respect to the statistical properties of the natural environment. Recent applications of this approach have been successful in the prediction of the linear filtering properties of ganglion cells and simple cells, but the relations between the environmental statistics and cortical nonlinearities, like those of end-stopped or complex cells, are not yet fully understood. Here we present extensions of our previous investigations of the exploitation of higher-order statistics by nonlinear neurons. We use multivariate wavelet statistics to demonstrate that a strictly linear processing would inevitably leave substantial statistical dependencies between the outputs of the units. We then consider how the basic nonlinearities of cortical neurons--gain control and ON/OFF half-wave rectification--can exploit these higher-order statistical dependencies. We first show that gain control provides an adaptation to the polar separability of the multivariate probability density function (PDF), and, together with an output nonlinearity, enables an overcomplete sparse coding. We then consider how the remaining higher-order dependencies between different units can be exploited by a combination of basic ON/OFF point nonlinearities and subsequent weighted linear combinations. We consider two statistical optimization schemes for the computation of the optimal weights: principal component analysis (PCA) and independent component analysis (ICA). Since the intermediate nonlinearities transform some of the higher-order dependencies into second-order dependencies even the basic PCA approach is able to exploit part of the redundancies. ICA ignores this second-order structure, but can exploit higher-order dependencies. Both schemes yield a variety of nonlinear units which comprise the typical nonlinear processing properties, such as end-stopping, side-stopping, complex-cell properties and extra-classical receptive field properties, but the 'ideal' complex cells seem only to occur with PCA. Thus, a combination of ON/OFF nonlinearities with an integrated PCA-ICA strategy seems necessary to exploit the statistical properties of natural images.

Algorithms↗

PubMed1998

Neural dynamics of motion processing and speed discrimination.

A neural network model of visual motion perception and speed discrimination is presented. The model shows how a distributed population code of speed tuning, that realizes a size-speed correlation, can be derived from the simplest mechanisms whereby activations of multiple spatially short-range filters of different size are transformed into speed-turned cell responses. These mechanisms use transient cell responses to moving stimuli, output thresholds that covary with filter size, and competition. These mechanisms are proposed to occur in the V1-->MT cortical processing stream. The model reproduces empirically derived speed discrimination curves and simulates data showing how visual speed perception and discrimination can be affected by stimulus contrast, duration, dot density and spatial frequency. Model motion mechanisms are analogous to mechanisms that have been used to model 3-D form and figure-ground perception. The model forms the front end of a larger motion processing system that has been used to simulate how global motion capture occurs, and how spatial attention is drawn to moving forms. It provides a computational foundation for an emerging neural theory of 3-D form and motion perception.

Form Perception↗

PubMed2006

Achieving the goal of halving global hunger by 2015.

The FAO World Food Summit (WFS) in 1996 set the goal of halving the numbers of the global population suffering hunger by the year 2015, which was later incorporated into the UN Millennium Development Goals (MDG) that commit the international community to an expanded vision of development, and one that vigorously promotes human development as the key to sustaining social and economic progress in all countries. The two targets under the first MDG goal to eradicate poverty and hunger call for halving the proportion of individuals who suffer from poverty and from hunger by 2015. This commitment is another instance of the international community through the UN system yet again renewing its efforts and setting a target and a time frame to deal with the global problem of hunger, poverty and malnutrition. To date, the efforts to reduce global hunger in the developing world have fallen far short of the pace required to meet these targets. There has no doubt been some progress and several countries in the developing world have proved that success is possible. The economic and societal costs to developing countries of not taking decisive action, and thus failing to achieve a reduction in hunger and undernutrition, including micronutrient malnutrition costs, are that every year five million children lose their lives, 220 million disability-adjusted life years are lost as a result of childhood and maternal undernutrition and billions of dollars are lost in productivity and incomes in these countries. Alongside this perennial problem in developing societies are emerging new epidemics of diet-related diseases resulting from the profound demographic changes, urbanization and the economic transition that is transforming and globalizing the food systems in these countries. Thus, many developing countries are facing new and additional challenges of co-existing hunger alongside the emergence of other forms of malnutrition. Meeting the WFS and MDG targets of achieving the goal of halving global hunger is urgent, and the question that needs to be addressed is not whether the international community can achieve this goal in time but whether it can afford not to.

Developing Countries↗

PubMed2003

[Multifocal steady-state pattern-reversal electroretinography in glaucoma patients].

AIM: This study was designed to answer the question of whether multifocal steady-state pattern-reversal electroretinography (ERG) is capable of detecting glaucomatous visual field defects. METHOD: Sixteen patients (28 eyes) and ten normal subjects (20 eyes) were examined. Multifocal pattern ERGs were recorded with the RETIscan system and DTL electrodes. We stimulated with a steady-state checkerboard pattern reversal (three reversals during 171 ms sweep length, congruent with 17.5 reversals/s). The multifocal pattern ERG amplitudes were evaluated using discrete Fourier transformation (DFT) across three reversals. In cases of advanced glaucoma, the DFT-calculated amplitudes were combined in hemispheres and checked for correlations with corresponding visual field defects. In all binocularly examined persons, side comparisons ("worse" eye vs "better" eye), and interindividual comparisons (glaucoma vs normal) were carried out. RESULTS: In interindividual comparisons and interocular side comparisons, significant amplitude reductions of the "worse" eyes were seen in the foveal records. No topographical correlation between multifocal pattern ERG amplitudes and visual field defects could be found. CONCLUSIONS: In glaucomatous visual field defects, multifocal steady-state pattern-reversal ERG using the present stimulation was significantly reduced in its foveal records but seems to be incapable of detecting them topographically.

Adult↗

PubMed2002

Active pulleys: magnetic resonance imaging of rectus muscle paths in tertiary gazes.

PURPOSE: The orbital layer of each rectus extraocular muscle (EOM) inserts on connective tissue, and the global layer inserts on the eyeball. The active-pulley hypothesis (APH) proposes that a condensation of this connective tissue constitutes a pulley serving as the functional origin of the rectus EOM, and that this pulley makes coordinated, gaze-related translations along the EOM axis to implement a linear ocular motor plant. This study was designed to measure gaze-related shifts in EOM pulley locations. METHODS: Magnetic resonance imaging (MRI) was performed in eight normal volunteers in 2-mm thickness coronal planes perpendicular to the orbital axis for nine cardinal gaze directions. Intravenous gadodiamide contrast was administered to define EOM tendons anterior to the globe equator. Paths of EOMs, defined by their area centroids, were transformed into an oculocentric coordinate system. Sharp inflections in EOM paths in secondary and tertiary gaze positions defined pulley locations which were then correlated with gaze direction and compared with theoretical predictions. RESULTS: Rectus pulley positions were consistent with a central primary position. In tertiary gaze positions, each of the four rectus pulleys translated posteriorly with EOM contraction and anteriorly with EOM relaxation by a significant (P < 0.02) amount predicted by the APH, but more than 100 times greater than the translation predicted by a passive pulley model. CONCLUSIONS: The APH prediction of coordinated anteroposterior shifting of EOM pulleys with gaze is quantitatively supported by changes in EOM path inflections among tertiary-gaze positions. Human rectus pulleys move to shift the ocular rotational axis to attain commutative behavior of the ocular motor plant.

Adult↗

PubMed2005

[Toric intraocular lenses for correction of persistent corneal astigmatism after penetrating keratoplasty].

PURPOSE: Cataract extraction with implantation of toric intraocular lenses (tIOL) is a new surgical option for correction of residual astigmatism following penetrating keratoplasty and cataract with only minimal direct manipulation of the graft. PATIENTS AND METHODS: We implanted an individually manufactured backtoric tIOL in 11 eyes of 9 patients. TIOL power calculation was done using vergence transformation in a paraxial space. RESULTS: Implantation and intraoperative alignment of tIOL were uneventful in all patients. Uncorrected visual acuity increased from 0.1+/-0.06 preoperatively to 0.47+/-0.18 (p=0.006) postoperatively. Best-corrected visual acuity changed from 0.23+/-0.18 preoperatively to 0.6+/-0.14 postoperatively (p=0.002). The refractive cylinder could be reduced from 7.0+/-2.6 D to 1.63+/-1.5 D (p=0.001) after surgery. We observed a small mean deviation from the target axis of 4.1+/-2.9 degrees (0-8 degrees ) after a mean follow-up time of 3.5 (2-7) months. CONCLUSION: TIOL implantation is a promising option for correction of high astigmatism following penetrating keratoplasty with only minimal direct surgical manipulation of the graft. Regular and symmetric corneal topography is essential for successful implantation of tIOL.

Aged↗

PubMedDate not supplied

Principles of ray tracing aberrometry.

PURPOSE: Of all transforms of an eye, aberrations are significant when higher visual acuity is to be achieved. Ray tracing aberrometry developed by the Institute of Biomedical Engineering (Kiev) and first tested at the Vardinoyannion Eye Institute of Crete is a promising technique for eye refraction aberration and refraction mapping. METHODS: The technique uses measurement of the position of a thin laser beam projected onto the retina. The beam is directed into the eye parallel to the visual axis. Each entrance point provides its own projection on the retina. A set of entrance points forms a set of projections. From these data, a refraction map is reconstructed as well as a point spread function of the eye. The total time of scanning over the whole aperture of the eye is within 10 to 20 ms and depends on the number of test points at the eye entrance, as well as on the number of independent measurements in each point. Configuration of the scanning pattern can be chosen by the operator. It may contain 60 to 400 points, each checked 1 to 5 times. RESULTS: Preliminary studies showed high reproducibility of results. Twenty pseudophakic eyes were subjected to 30 consecutive measurements each. Ninety-five percent of all measured values were within +/-0.20 D of declination from the mean. CONCLUSIONS: Ray tracing aberrometry is a flexible technology for eye investigation. It can be adapted to any laser technique of vision correction Its further development should be oriented on laser-linked applications of the refraction driven refractive surgery.

Accommodation, Ocular↗

PubMed2000

A Fraser illusion without local cues?

In the well-known Fraser illusion, a line composed of tilted elements itself appears tilted. The standard explanation of this illusion has been that the global orientation of the line is in some way influenced by the local orientation of the elements. The illusion was recreated using a texture composed of collinear Gabor stimuli, which were vertical. There was no local tilt. The illusory tilt was produced by gradually shifting the phase of the successive Gabors along each line. Although the 2D Fourier transform of this global pattern peaks at off-vertical orientations, the local energy of the patches is predominantly vertical. How does the visual system nevertheless pick up this global information? This can be explained by elongated linear filters, or a phase-tuned second-stage mechanism. We examined the first theory using a stereoscopic demonstration. When lines of opposite tilt are presented in the two eyes, they combine binocularly to produce stereoscopic slant. We tested whether the illusory tilts in the phase-shifted Gabors texture give stereoscopic slant, when opposite tilts are presented to the two eyes. They do not. Instead, stereoscopic depth is dominated by the local phase-disparity of the individual patches. This indicates that the illusion is not present at the stage of linear filters, which are input to stereo, but must involve second-stage interactions or collators.

Cues↗

PubMed1978

The development of the parachute reaction: a visuo-vestibular response.

The development of the parachute reaction as a postural response has been tested under various optic stimuli in normal and statomotorically retarded infants. Complete reaction consists in symmetric extension of the arms with extension and spreading of the fingers on quick approach to visual surface. Using a glass plate with three different sized stimulus patterns the parachute response is scored as complete or incomplete. The complete reaction to large visual surface develops significantly earlier than to small visual surface. The response also requires simultaneously a visual and a vestibular sensory input. The developmental course of the parachute reaction is statistically significant linear correlated in double logarithmic transformation to the stimulus pattern and to the age indicating a complex biological maturating process. When the whole retinal area was stimulated by moving visual scenes similar to normal environmental conditions the reaction starts with about 4 months of age and is fully developed from 9 months onwards. The time of quickest development is around 6.3 months of age, a period where locomotor abilities shift from horizontal postiion to active verticalisation of the body. In statomotorically retarded infants the response develops significantly later according to their active motor behaviour. Brain integration and computing centers of sensory afferent input could be multilevel from reticular formation to cerebral cortex, wherein the latter, probable the parietal lobe should play the major role. It is concluded that the parachute reaction results from a combined visuovestibular mechanism of interaction in connection with sufficient kinesthetic experience in visuo-motor behaviour.

Age Factors↗