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E Hita

Publications and source records attributed to E Hita.

13 recordsLinked to original sources
PubMed2001

Analysis of discrimination threshold on the tritan axis.

Discrimination thresholds on the tritan axis were obtained for an extensive group of 66 stimuli: in some of the stimuli, S-cone trolands were held constant by keeping the product of the S-cone excitation level and the luminance unchanged, while in others only the luminance was changed to establish various S-cone troland values. These thresholds depended clearly on the S-cone value of the stimuli, while they remained almost constant against the retinal illumination. Thus, we noted that the excitation of the L - 2M channel had practically no influence over the discrimination threshold on the tritan axis, although this independence of delta S from L - 2M was not so obvious when the S value was high. With our data, we performed different fits, and found that the fit including the terms S, (L - 2M) and (L + M) adapted better to our results.

Adult↗
PubMed2001

Optical measurement of cardiac rhythm using a personal computer with telediagnosis possibilities.

A system that enables the automatic measurement of cardiac rhythm and the quantity of oxygen in the blood has been designed, constructed, and patented. Equipped with the appropriate software, this system registers this information and represents it numerically, in the form of a graph, which can then be printed as a detailed record of cardiac rhythm. This system aids in the determination of cardiac pathologies, and also enables the information to be sent to medical professionals to perform telediagnosis. The apparatus is based on the measurement (sampling) of noninvasive medical parameters. The apparatus is intended to cover a broad range of requirements and needs, as can be used by medical professionals (to detect pathologies related to the pumping and circulation of blood in the body) as well as by lay people who might wish to monitor or gain information concerning their cardiac rhythm and the general functioning of their heart. Thus, the system is designed to be clear and concise in its information as well as easy to use, especially for people unrelated to the medical profession. The way to constructing this system is explained in detail.

Cardiovascular Diseases↗
PubMed2000

Visual system's adjustments to illuminant changes: heuristic-based model revisited.

This study evaluates the effect of illuminant changes along the two post-receptoral mechanisms: red-green (L - 2M) and yellow-blue (L + M - S). By means of a CRT colour monitor, Mondrian-type scenes were simulated and a series of asymmetric colour matches were made with five test illuminants. The standard objects comprising the scenes were simulations of surfaces under equal-energy illuminant and were selected according to lines of equal excitation of the red-green and the yellow-blue mechanisms. Results show that observers' matches are well predicted by assuming affine transformations between test and standard illuminant conditions. The best linear fits derived from the data corroborates the previous heuristic-based algorithms [Zaidi Q. (1998) Journal of the Optical Society of America A. 7. 1767-1776] although some discrepancies were found. Results along red-green mechanism confirm that the significant effect of the illuminant is an additive change along this axis, while data for yellow-blue mechanism suggest that illuminant induces not only multiplicative changes along this axis but additive too. In addition, we found that memory factors involved in the experiment could influence the observers' matches and would be taken into account as responsible of the differences found between the yellow-blue and the red-green systems.

Adaptation, Ocular↗
PubMed2000

Changes in stereoscopic depth perception caused by decentration of spectacle lenses.

The effect that decentered spectacle (ophthalmic) lenses exert on depth perception has been studied, evaluating stereopsis through the disparity range (maximum horizontal disparity) for random-dot stereograms (RDS). The results show that variations in fusional convergence due to increments of decentration can diminish the stereopsis in observers, reducing the region within which stereoscopic correspondence can take place. Decreases in disparity ranges were found for vertical and horizontal prismatic effects, although the prismatic effect necessary for this was less in the vertical case. A decreased disparity range has also been confirmed with figural-stimuli stereograms and using prisms for generating the prismatic effects.

Adaptation, Ocular↗
PubMed2000

Towards a colorimetric characterization of the human iris.

We propose a new approach to the quantitative determination of the iris colour through the spectroradiometric measurement of a set of 72 artificial irises under controlled illumination and geometry. The spread of these samples in the CIELAB colour space indicates no clearly distinguished groups within the set analysed. Colour measurements for different points of these irises and for the overall irises (pupil and specular image of the light source included) are well correlated. Complementary colour measurements were also performed for the irises of 25 ocular prostheses and 40 real observers. All these colour measurements appear to be quite consistent, the average standard deviation of any of the three a*, b*, L* co-ordinates being lower than 1.0 units. In a visual experiment where 11 normal observers matched the 25 ocular prostheses using the 72 artificial irises, the results indicate that a simple criterion based on the lowest colour-difference agreed with the observers' judgements in only 18% of the cases. This result suggests that, although colour appears to be a major parameter in the overall characterization of the human iris, additional factors such as patterns or textures should also be considered.

Colorimetry↗
PubMed1997

Influence of the luminance and opponent chromatic channels on stereopsis with random-dot stereograms.

The present work examines the relationship between random-dot stereograms (via the disparity range parameter) and color-vision mechanisms (via the luminance channel and red-green and tritan directions at isoluminance). The results clearly indicate that the variations in the stereograms along red-green confusion lines contribute to stereopsis. Stereoscopic perception depends on spatial information for stereograms generated with variations along tritan confusion lines. For observers who perceive stereopsis via tritan directions, the results show a gradation in the disparity range, with the disparity range for stereograms generated by luminance variations being greater than for stereograms generated in red-green directions; the latter range is, in turn, greater than for stereograms generated along tritan directions.

Color Perception↗
PubMed1997

Performance of a color indicator in a disinfecting solution for the maintenance of soft contact lenses.

An experimental study of Allergan's Oxysept Comfort system was performed by measuring the slight reddish hue that appears in the disinfecting solution, indicating to the users that their lenses are again ready to be worn. The temporal evolution of the color of the solution has been measured under standardized conditions and analyzed in the CIELAB system, from the perspective of the typical threshold discrimination of the human eye. Color differences between neutralized and non-neutralized solutions occurred in an appropriate direction of the color space to enhance discrimination and were clearly perceptible by normal observers (greater than 9.7 +/- 1.2 CIELAB units). Colorimetric analyses have been used to draw conclusions regarding observers with defective color vision. The color of the solution changes abruptly, approximately 25 min after the neutralization process begins, and remains nearly constant after about 60 min, this agreeing well with the temporal evolution of the hydrogen peroxide concentration.

Color↗
PubMed1994

Variations in corneal sensitivity with hydrogel contact lenses.

Changes in corneal sensitivity were studied in two groups of healthy subjects who wore hydrogel contact lenses: 44 persons whose lenses contained 38% water, and 23 who wore lenses of 55% water content. Corneal sensitivity decreased in both groups during the first 8 h following insertion; the decrease was more marked in the group who wore 38% water lenses. Changes in corneal tactile sensitivity were greater in women than in men, and determinations in different corneal zones showed that the central zone was less affected in sensitivity than any of the peripheral zones. After lenses were removed, tactile sensitivity showed full recovery within 4 h.

Adolescent↗
PubMed1989

Appearance of color matchings under various chromatic adaptation conditions.

Three chromatic reference stimuli (red, green, and blue) seen under five adaptation conditions (red, green, blue, achromatic, and darkness) were appearance-matched to subsequent color stimuli seen under achromatic conditions. The experimental results have been used to verify the opponent-color color-vision model and also to check the validity of some of the published transformation equations for predicting the tristimulus values of colors matched to a reference stimulus seen under different chromatic-adaptation conditions. It is concluded that the extant transformation laws are not sufficiently general to be applied to all adaptation conditions.

Adaptation, Ocular↗
PubMed1988

Color-prediction discrepancies and differential chromaticity thresholds with photopigment bleaching.

The differential chromaticity thresholds of three color stimuli have been determined from metameric matches carried out during the cone-plateau period after photopigment bleaching. The results are compared with some recently published ones [E. Hita, L. Jiménez del Barco, and J. Romero, J. Opt. Soc. Am. A 3, 1203 (1986)] obtained under similar experimental conditions but without prior photopigment bleaching. The possible effects of rod intrusion on color-prediction discrepancies are discussed in the light of both sets of results. Under our experimental conditions, with foveal fields of 3 deg, luminance within the low photopic level, and sets of primary colors produced by filters of differing spectral bandwidth, the rod intrusion effect can be ruled out as a possible cause of color-prediction discrepancies, although it does appear to produce variations in the sizes of the discrimination ellipses and in their orientation.

Acclimatization↗
PubMed1986

A comparative study of successive and simultaneous methods in colour discrimination.

Simultaneous and successive methods of comparison of stimuli are studied by comparing experimental results of colour discrimination experiments. In this way, colour differential thresholds for two normal observers and four different stimuli were measured by the two methods. In most cases, the capacity to discriminate colour decreased when the successive method was used, although no differences were found in qualitative aspects of discrimination. These results differ somewhat from previous reports in this field, probably because of experimental differences in the method of obtaining the thresholds.

Color Perception↗
PubMed1986

Differential color thresholds from metameric matches: experimental results concerning failures of colorimetric additivity.

The differential chromaticity thresholds obtained by varying degrees of metamerism have been evaluated for five target chromaticities. Differences have been found between the chromaticities predicted by the CIE-1931 standard observer and those actually observed under our experimental conditions, with foveal fields of 3 degrees, luminance within the low photopic level, and sets of primary colors produced by filters of differing spectral bandwidths. Failures of colorimetric additivity under these experimental conditions are discussed. The results have also been analyzed by using other sets of color-matching functions, i.e., Judd's proposed modification at short wavelengths and also the supplementary standard observer, CIE-1964.

Color↗