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PubMed1980

What is suppressed during binocular rivalry?

To answer the question 'what is suppressed during binocular rivalry?" a series of three experiments was performed. In the first experiment observers viewed binocular rivalry between orthogonally oriented patterns. When the dominant and suppressed patterns were interchanged between the eyes observers continued seeing with the dominant eye, indicating that an eye, not a pattern, is suppressed during rivalry. In a second experiment it was found that a suppressed eye was able to contribute to stereopsis. A third experiment demonstrated that the predominance of an eye could be influenced by prior adaptation of the other eye, indicating that binocular mechanisms participate in the rivalry process.

Adaptation, Ocular↗
PubMed2003

Pulfrich on wheels.

Explore the source record for details and available documents.

Adaptation, Ocular↗
PubMed2002

Vertical disparity can alter perceived direction.

It has been well established that vertical disparity is involved in perception of the three-dimensional layout of a visual scene. The goal of this paper was to examine whether vertical disparities can alter perceived direction. We dissociated the common relationship between vertical disparity and the stimulus direction by applying a vertical magnification to the image presented to one eye. We used a staircase paradigm to measure whether perceived straight-ahead depended on the amount of vertical magnification in the stimulus. Subjects judged whether a test dot was flashed to either the left or the right side of straight-ahead. We found that perceived straight-ahead did indeed depend on the amount of vertical magnification but only after subjects adapted (for 5 min) to vertical scale (and only in five out of nine subjects). We argue that vertical disparity is a factor in the calibration of the relationship between eye-position signals and perceived direction.

Adaptation, Physiological↗
PubMed2002

From visual function deficiency to handicap: measuring visual handicap in Mali.

BACKGROUND/AIMS: Blindness is a major public health problem in developing countries, even though most could be prevented by relatively simple hygienic and medical interventions. Relatively few patients use the quality health care services available, despite their low cost, due to problems of access or socio-cultural barriers. This health services research project stressed the need for measurement of subjective self-perceived health. The objectives of this study were twofold: a) To translate, adapt and integrate the cultural context found in Mali and validate two instruments for measuring, respectively, perceived vision and quality of life. b) To study the relationship between these variables and visual deficiencies by gender. METHODS: The perceived vision and quality of life questionnaires were based on a translation of the Aravind questionnaire, adapted to Mali. The resulting perceived vision questionnaire comprises 13 questions, grouped according to five subscales (global vision, visual perception, sensory adaptation, visual field and depth perception). Furthermore, the 13 questions on quality of life were grouped into four subscales (personal care, mobility, social life and psychological). For both questionnaires, a global score could be computed. These two questionnaires were administered to a representative sample of 203 subjects with impaired vision, aged over 40, in a rural area in Mali. RESULTS: The acceptability of the questionnaires was good (1% missing data). The convergent validity was adequate for all but one subscale (psychological). The discriminate validity is acceptable for three of the six subscales where measurement can be made (visual perception, personal care, mobility). The Cronbach alpha coefficients indicate good reliability for the global scores. CONCLUSIONS: Analysis of mean results confirms the validity of the International Classification of Disease (ICD) definition of blindness (seeing less than 0.05 results in a steep decrease in quality of life). Moreover, blindness affects the quality of life of women more severely than that of men; this may be related to the availability of social support.

Adult↗
PubMed2005

Perceptions of the role of maternal nutrition in HIV-positive breast-feeding women in Malawi.

A neglected issue in the literature on maternal nutrition and HIV is how HIV-positive women perceive their own bodies, health, and well-being, particularly in light of their infection, and whether these perceptions influence their infant feeding practices and their perceived ability to breast-feed exclusively through 6 mo. We conducted formative research to better understand breast-feeding practices and perceptions, and to inform the Breastfeeding, Antiretroviral, and Nutrition (BAN) Study, a clinical trial to evaluate antiretroviral and nutrition interventions to reduce mother-to-child transmission of HIV during breast-feeding in Lilongwe, Malawi. Twenty-two HIV-positive women living in semi-rural areas on the periphery of Lilongwe participated in in-depth interviews. In an adaptation of the body-silhouette methodology, nine culturally appropriate body silhouettes, representing a continuum of very thin to very large shapes, were used to elicit women's views on their present, previous-year, and preferred body shapes, and on the shape they perceived as healthy. The narrative scenario method was also used to explore women's views on 2 fictional women infected with HIV and their ability to exclusively breast-feed. Women perceived larger body shapes as healthy, because fatness is considered a sign of good health and absence of disease, and many recognized the role of nutrition in achieving a preferred or healthy body shape. Several women believed their nutritional status (body size) was declining because of their illness. Women were concerned that breast-feeding may increase the progression of HIV, suggesting that international guidelines to promote appropriate infant feeding practices for infants whose mothers are infected with HIV should focus on the mother's health and well-being, as well as the infant's.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Phylogenetic relationships within the Alcidae (Charadriiformes: Aves) inferred from total molecular evidence.

The Alcidae is a unique assemblage of Northern Hemisphere seabirds that forage by "flying" underwater. Despite obvious affinities among the species, their evolutionary relationships are unclear. We analyzed nucleotide sequences of 1,045 base pairs of the mitochondrial cytochrome b gene and allelic profiles for 37 allozyme loci in all 22 extant species. Trees were constructed on independent and combined data sets using maximum parsimony and distance methods that correct for superimposed changes. Alternative methods of analysis produced only minor differences in relationships that were supported strongly by bootstrapping or standard error tests. Combining sequence and allozyme data into a single analysis provided the greatest number of relationships receiving strong support. Addition of published morphological and ecological data did not improve support for any additional relationship. All analyses grouped species into six distinct lineages: (1) the dovekie (Alle alle) and auks, (2) guillemots, (3) brachyramphine murrelets, (4) synthliboramphine murrelets, (5) true auklets, and (6) the rhinoceros auklet (Cerorhinca monocerata) and puffins. The two murres (genus Uria) were sister taxa, and the black guillemot (Cepphus grylle) was basal to the other guillemots. The Asian subspecies of the marbled murrelet (Brachyramphus marmoratus perdix) was the most divergent brachyramphine murrelet, and two distinct lineages occurred within the synthliboramphine murrelets. Cassin's auklet (Ptychoramphus aleuticus) and the rhinoceros auklet were basal to the other auklets and puffins, respectively, and the Atlantic (Fratercula arctica) and horned (Fratercula corniculata) puffins were sister taxa. Several relationships among tribes, among the dovekie and auks, and among the auklets could not be resolved but resembled "star" phylogenies indicative of adaptive radiations at different depths within the trees.

Alleles↗
PubMed1980

Adaptation to prism-induced heterophoria.

Measurements of the way the oculomotor system adapts to prism-induced heterophorias have been made in eight normal subjects. Adaptation to 2 delta vertically and, on separate occasions, to 6 delta horizontally was found to be substantially completed after only 2-3 minutes of binocular visual experience. The form of the adaptive process for distant targets was asymmetrical in the horizontal meridian, being faster after the insertion of 6 delta base-out than for 6 delta base-in. This asymmetry largely disappeared for near vision.

Adaptation, Physiological↗
PubMed1982

Effect of orthoptics upon the ability of patients to adapt to prism-induced heterophoria.

In a previous study we showed that subjects with abnormal binocular vision either lacked or had a deficient ability to adapt their oculomotor systems to a prism-induced heterophoria. In this study we report on the results of an experiment designed to establish whether the adaptation ability improves in patients who are successfully treated, by means of orthoptics, for convergence insufficiency. In all seven patients examined, we found an improved ability to adapt. Whereas at the beginning of the experiment only two patients fell within the 95% confidence limits of the norm, at the end five patients fell within these limits. These results demonstrate that the success of orthoptics in relieving symptoms is associated with an improved ability to adapt to prism-induced heterophoria.

Adaptation, Ocular↗
PubMed1974

Interocular transfer of a visual after-effect in normal and stereoblind humans.

1. Following inspection of a high contrast grating a test grating of a slightly different orientation will briefly appear rotated from its true orientation in a direction opposite to that of the adapting grating.2. The extent of interocular transfer of this phenomenon (the tilt after-effect) was measured in a number of normal subjects and in four subjects (three of whom had a strabismus) who lacked stereopsis.3. In contrast to the normal subjects, none of the four stereoblind subjects showed any interocular transfer of the tilt after-effect. Amongst the normal subjects the extent of transfer of this after-effect was positively correlated with the subject's stereoacuity. Maximum transfer (70%) was found in the subject with the best stereoacuity. In many subjects transfer was greater from the dominant eye to the non-dominant eye than vice versa.4. By analogy with experiments on cats deprived of congruent visual input to the two eyes early in life it is argued that the stereoblind subjects lack any binocularly driven cortical neurones.

Adaptation, Ocular↗
PubMed2000

Study of near infrared technology for intracranial hematoma detection.

Although intracranial hematoma detection only requires the continuous wave technique of near infrared spectroscopy (NIRS), previous studies have shown that there are still some problems in obtaining very accurate, reliable hematoma detection. Several of the most important limitations of NIR technology for hematoma detection such as the dynamic range of detection, hair absorption, optical contact, layered structure of the head, and depth of detection are reported in this article. A pulsed light source of variable intensity was designed and studied in order to overcome hair absorption and to increase the dynamic range and depth of detection. An adaptive elastic optical probe was made to improve the optical contact and decrease contact noise. A new microcontroller operated portable hematoma detector was developed. Due to the layered structure of the human head, simulation on a layered medium was analyzed experimentally. Model inhomogeneity tests and animal hematoma tests showed the effectiveness of the improved hematoma detector for intracranial hematoma detection.

Absorption↗
PubMedDate not supplied

Extracorporeal ablation of liver tissue by high-intensity focused ultrasound.

High-intensity focused ultrasound (HIFU) may produce a well-delineated lesion of coagulation necrosis in deep organs, by means of an extracorporeal transducer. Applications of this method to the liver in animal models have been studied for many years. The effects of HIFU on the normal liver parenchyma and on hepatic tumors are reviewed. In the normal rabbit liver in vivo we showed the relation between intensity levels and exposure times and the need to adapt intensity to the depth of the target. No severe complications were observed when an intensity of 1,000 W/cm2 was used. HIFU is a noninvasive method for the local destruction of liver tumors. In experimental models, safety and efficacy were demonstrated. HIFU may be interesting for the treatment of some human liver tumors.

Animals↗
PubMed1989

On the evidence for a 'pure' binocular process in human vision.

Wolfe (1986, Psychol. Rev. 93, 269-282) proposed a model of human binocular vision based on the assumption of two functionally distinct classes of binocular neuron. These neurons may be regarded as logical AND and OR gates. In the present paper we assess the evidence relevant to this assumption. We find that while both types of binocular neuron have been described in the cortex of cat and monkey, there is no indication that they form functionally separate populations. Critical analysis of the psychophysical evidence for AND and OR channels in human vision suggests that much of the data presented in favor of an AND channel is subject to alternative interpretations. We conclude that the available data are not consistent with the existence of separate channels as proposed by Wolfe.

Adaptation, Ocular↗