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At least 865 records · Page 48Linked to original sources
PubMed2003

Shade matching in restorative dentistry: the science and strategies.

Closely matching natural teeth with an artificial restoration can be one of the most challenging procedures in restorative dentistry. Natural teeth vary greatly in color and shape. They reveal ample information about patients' background and personality. Dentistry provides the opportunity to restore unique patient characteristics or replace them with alternatives. Whether one tooth or many are restored, the ability to assess and properly communicate information to the laboratory can be greatly improved by learning the language of color and light characteristics. It is only possible to duplicate in ceramic what has been distinguished, understood, and communicated in the shade-matching process of the natural dentition. This article will give the reader a better understanding of what happens when incident light hits the surface of a tooth and give strategies for best assessing and communicating this to the dental laboratory.

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PubMed1991

Virtually real.

Explore the source record for details and available documents.

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PubMed1990

Experimental evidence for a transient system deficit in specific reading disability.

This paper summarizes the experimental evidence for a transient system deficit in specific reading disability. Differences have been found between controlled readers and specifically disabled readers in measurements of visible persistence, pattern contrast sensitivity and temporal or flicker contrast sensitivity. This transient system deficit was found in approximately 75% of the specifically reading disabled subjects tested. A further series of experiments failed to demonstrate differences in sustained system function between the two groups. Evidence is also presented which suggests that the visual system deficit precedes the reading disability. Possible mechanisms of the impact of a transient system deficit on reading are discussed.

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PubMed1989

The changing face of visual persistence.

In three experiments, the effect of target luminance on estimates of visual persistence was determined on a popular successive-field task. Even though the experiments differed from each other only in terms of minor changes in stimulus conditions, very different effects were obtained across the three experiments. The different findings were attributed to the often overlooked roles of masking and target degradation on tasks of persistence. Implications for the numerous contradictory findings in the persistence literature are discussed, and the current popularity of the successive-field task is questioned.

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PubMed1987

Photoreceptor signals and vision. Proctor lecture.

In recent years, there has been rapid progress in understanding the properties and mechanism of generation of the light-evoked electrical signals of vertebrate rods and cones. The graded hyperpolarization that carries information over the length of the cell is generated by closure of cation-selective aqueous pores in the surface membrane of the outer segment. These pores are controlled cooperatively by cyclic GMP, which acts continuously in darkness to keep the pores open. Photoisomerization of rhodopsin or cone pigment produces the rapid amplified activation of phosphodiesterase, which lowers the concentration of cGMP, thereby lowering the conductance of the surface membrane. Calcium ions, once thought to relay excitation to the light-sensitive channels, do not play this role. Instead, they appear to participate in a feedback control mechanism that regulates the nucleotide cascade. Although some general features of the transduction mechanism are now understood, a number of important questions remain. How is the nucleotide cascade shut off? Where does Ca act? What is the structure of the light-sensitive channel? How are stereotyped single photon responses produced? Primate photoreceptors are no longer off limits to single cell electrophysiology. Analysis of the response properties and dark noise of primate rods gives a physiological basis for several fundamental features of human rod vision: single photon detection, poor temporal resolution, the "dark light," rod saturation, scotopic spectral sensitivity, and, perhaps, after-image signals. Primate cones show less sensitive but faster responses shaped by a resonance which may figure in the flicker sensitivity of human cone vision. The spectral sensitivity of the three types of primate cones has been determined over the entire visible region. These sensitivities satisfactorily predict human color matching. The spectral sensitivity curves indicate that the pigment in a given cone is very pure, and that individual cones of a given type normally contain pigments with very similar or identical spectral properties.

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PubMed1988

Chromatic aftereffects associated with a night vision goggle simulation.

A visual perception experiment was conducted to determine the chromatic aftereffects of viewing a yellow-green field that simulated the display of current night vision goggles. Six females and two males served as subjects in a color-naming procedure. Subjects sequentially viewed an adaptation field, which was either yellow-green or white, and small colored targets presented on a CRT display. The time required to name the color of the targets was found to be dependent on the color of the adaptation field, the color of the target, and the interaction of these two variables. It was recommended that the effects of attenuation of the luminance of the night vision goggles be studied, and that color cockpit displays be redundantly coded whenever possible.

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PubMed1986

Cotard's syndrome in a patient with coexistent Capgras' syndrome, syndrome of subjective doubles, and palinopsia.

The hallmark of Cotard's syndrome is the delusion of being dead. It is usually seen in affective disorders, and its existence as a separate entity is controversial. A patient is described who presented with paranoid schizophrenia, Cotard's syndrome, the misidentification syndromes of Capgras and subjective doubles, and palinopsia (visual perseveration). Focal theories for these conditions are briefly outlined and the patient is discussed with reference to them. It is proposed that this case supports the concept that Cotard's syndrome is a distinct disorder. The possibility of cerebral dysfunction in the confluence of the parietal, temporal, and occipital regions accounting for this specific clinical presentation is considered.

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PubMed1985

Palinopsia and bitemporal visual extinction on fixation.

Spontaneous palinopsia (visual perseveration) and bitemporal visual extinction provoked only by ocular fixation developed in a patient with multiple sclerosis who had chronic bilateral retrobulbar optic neuritis. There were no signs of hemispheral compromise. The intermittent visual symptoms seemingly arose from the lesioned optic nerves, but were probably integrated at a cortical level. Palinopsia, classically considered diagnostic of posterior hemispheral cortical lesions, can also occur in patients with peripherally placed lesions of the visual pathways.

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