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Biomedical subjects

Y Ejima

Publications and source records attributed to Y Ejima.

At least 91 records · Page 5Linked to original sources
PubMed1985

Effect of localized grating adaptation as a function of separation along the length axis between test and adaptation areas.

Aftereffect following adaptation to localized gratings was measured as a function of the separation along the length axis between test and adaptation gratings. When the adaptation gratings were located on or near the retinal area occupied by the test grating, contrast sensitivity greatly decreased. When the adaptation gratings were spatially separated from the test grating, contrast sensitivity significantly increased. This property is similar to that which was observed in our previous study, in which the adaptation gratings were displaced from a test grating along the modulation axis. The facilitatory aftereffect of the grating adaptation can be accounted for by assuming that there may exist two mechanisms involved in the adaptation process; one is a center mechanism responsible for the detection of a test pattern, its adaptation producing a reduction in responsiveness; the other is a surround mechanism which tonically inhibits the center mechanism, its adaptation resulting in an increase in the sensitivity of the center mechanism by releasing the tonic inhibition. The spatial property of the adaptation effect may reflect the nature of spatial integration process of the center and surround mechanism.

Adaptation, Ocular↗
PubMed1985

Effect of light adaptation on the perceptual red-green and yellow-blue opponent-color responses.

Spectral sensitivities of the red-green and yellow-blue opponent-color responses were determined under broad-band light adaptation for the light-adaptation levels of 5 to 5000 Td. With changing light-adaptation level, the spectral-sensitivity functions of the opponent-color systems change in shape, especially in the short-wavelength region of the spectrum. The light-adaptation effect on the red-green responses can be ascribed to the changes at the cone receptor level, whereas the light-adaptation effect on the yellow-blue responses can be ascribed to the changes at two sites, i.e., at the cone receptor site and at the opponent site.

Adaptation, Physiological↗
PubMed1984

The neon color effect in the Ehrenstein pattern. Dependence on wavelength and illuminance.

The neon color effect can be described as an illusory spread of color surrounding colored lines embedded in certain line gaps. The effect is seen in the Ehrenstein pattern if colored crosses are added to the central gaps so as to connect the inner tips of the pattern. Experiments were conducted to explore the dependence of this neon color effect on the wavelength and retinal illuminance of the inducing lines. The following results were obtained: neon color effects are strong when the wavelength of the crosses is in the short- (less than 480 nm) or long-wave part of the spectrum (greater than 620 nm) and the wavelength of the Ehrenstein pattern is in the middle-wave part (500-580 nm). Effects are weak or absent when the crosses and the pattern have similar wavelengths. The neon color effect is just detectable when the ratio between the retinal illuminances of the Ehrenstein pattern and the crosses ranges from 0.1 to 0.8. The neon color effect is maximal at illuminance ratios ranging from 0.8 to 8. The strength of the neon color effect is independent of the illuminance level of the crosses if the illuminance ratio to the Ehrenstein pattern is maintained.

Color Perception↗
PubMed1984

Bezold-Brücke hue shift and nonlinearity in opponent-color process.

Dependence of the red-green and yellow-blue opponent-color responses on stimulus intensity was examined. First, each of four chromatic responses was measured as a function of illuminance by using a hue cancellation procedure. The cancellation redness and greenness increased proportionally with illuminance, but the cancellation yellowness and blueness did not. Second, the relative growth rate with illuminance between the two opponent-color systems was determined by using a technique of the estimation of hue ratio. The result gave a support to the view that the Bezold-Brücke hue shift is contributed mainly by the opponent-colors neural interactive process. It was suggested that the nonlinear transduction of the yellow-blue system, producing the hue shift, might have a close relation to the change with stimulus intensity in the relative sensitivity of the short-wavelength cone mechanism to the long- and middle-wavelength cone mechanisms.

Color Perception↗
PubMed1984

Change in detection threshold caused by peripheral gratings: dependence on contrast and separation.

The detection threshold for a sinusoidal grating in the presence of peripheral gratings was determined as a function of peripheral-grating contrast and separation between the two gratings, with phase relation as a parameter. The result showed that the peripheral gratings, in the range of low contrast, yielded a facilitatory or an inhibitory effect dependent on the phase relation, but in the range of high contrast, yielded an inhibitory effect irrespective of the phase relation. This suggests that two separate mechanisms may underlie the grating induction effect of the detection threshold.

Form Perception↗
PubMed1984

Facilitatory and inhibitory after-effect of spatially localized grating adaptation.

Aftereffects of spatially localized grating adaptation were measured for different locations of the adaptation grating relative to test grating. When the adaptation grating was located on or near the retinal area occupied by the test grating, contrast sensitivity was markedly reduced. When the adaptation grating was spatially separated from the test grating, contrast sensitivity was significantly increased. This aftereffect of spatially localized grating adaptation suggests that spatial-frequency-selective detectors are not spatially independent, but tonically inhibited by spatially contiguous mechanisms. Thus the adaptation of these mechanisms might cause an increase in contrast sensitivity of detectors subserving the test grating.

Adaptation, Ocular↗
PubMed1984

Spatial properties of red-green and yellow-blue perceptual opponent-color response.

Opponent color responses for an equal illuminance spectrum were measured for field size from 10' to 2 degrees, by means of a hue cancellation procedure. Results showed that when the field diameter was increased, the red and yellow response relatively increased and the green and blue response relatively decreased. There existed a different spatial property between the red-green and yellow-blue opponent-color response function. The results were compared with the optical density hypothesis of the cone visual pigments and with the neurophysiologically obtained receptive field properties of opponent-color cells.

Color Perception↗
PubMed1983

Chromatic induction as a function of wavelength of inducing stimulus.

Induced chromatic effects were determined for monochromatic, equal-luminance inducing stimuli from 460 to 680 nm by using a hue-cancellation procedure. The observed red-green-and yellow-blue-induced chromatic-response functions, which were different from the prediction based on the opponent-color hypothesis, could accurately explain the characteristics of the simultaneous color contrast effect. Good linear fits were obtained for the red-green function with a linear combination of R and G cones and for the yellow-blue function with a linear combination of R and B cones. These findings suggest that the opponent mechanisms for color contrast may be different from those for homogeneous color.

Adult↗
PubMed1983

Functional relationship between chromatic induction and luminance of the inducing stimulus.

We determined the functional relationship between chromatic induction and luminance of the inducing stimulus for different spatial conditions and assessed whether the effects of luminance and spatial variables could be explained in terms of the total effective energy in the inducing field. The result showed that the relationship between chromatic induction and luminance of the inducing stimulus could be mathematically expressed by an exponential function of the luminance ratio between the test and inducing stimuli and that the coefficient of the exponent was independent of spatial variables, i.e., area and separation. This led to the conclusion that a luminance ratio between two fields, rather than a quantum energy of the inducing field, was a relevant determinant of the effect of luminance of the inducing stimulus on chromatic induction.

Adult↗
PubMed1983

Relationship between chromatic induction and spatial variables: an integrated explanation in terms of element-contribution function.

Chromatic induction as a function of separation and as a function of area was determined by a hue-cancellation procedure. Both functions obtained were expressed by exponential functions with similar exponential coefficients. This led to the derivation of an element-contribution function, based on a linear summation model, that could explain both the relationship between chromatic induction and separation and that between chromatic induction and area. The effects of separation and area on chromatic induction could readily be determined in terms of an element-contribution function. In addition, the induction area that is due to a blue inducing stimulus was larger than those that are due to the other inducing stimuli, suggesting that the summation area of the blue response was larger than those of the other chromatic responses.

Adult↗
PubMed1983

Chromatic valence and hue sensation.

Red-green and yellow-blue chromaticnesses were scaled for various monochromatic lights by a just-noticeable-difference method. The just-noticeable difference of each chromaticness, i.e., redness, greenness, yellowness, or blueness, was defined by the change of the canceling light intensity that was required to produce a just-noticeable difference in the amount of the opponent-hue attribute of each monochromatic light. The results showed that an approximately logarithmic transformation took place at the two opponent-color coding systems and that there existed an interaction between red-green and yellow-blue opponent-color coding systems in such a manner that the effective contribution of one opponent-color response to the perceived opponent-hue attribute was reduced by increasing the magnitude of the other opponent-color response. This interaction is considered to be responsible for the well-known veiling effect.

Adult↗
PubMed1983

Effects of high-contrast peripheral patterns on the detection threshold of sinusoidal targets.

Detection thresholds of sinusoidal gratings in the simultaneous presence of high-contrast peripheral masking stimuli partially overlapping the test gratings were determined as a function of the separation between the center of the test grating and the peripheral stimulus by a two-alternative forced-choice method. The results showed that the threshold-elevating effect of simultaneously present peripheral masking stimuli depends on how much of the test grating is left unexposed. An additional experiment, in which the detection thresholds in the absence of the peripheral stimulus were determined as a function of the number of cycles of the test grating, enabled us to show that the threshold-elevating effect is somewhat higher than the effect of simply cutting the test grating down in size. The threshold-elevating effects caused by high-contrast peripheral masking stimuli can be explained in terms of a lateral inhibition and a probability summation across space, taking into account the nonuniform sensitivity across the visual field.

Female↗
PubMed1982

Radiosensitivity of fibroblasts from patients with retinoblastoma and chromosome-13 anomalies.

Diploid fibroblast cell strains derived from 14 patients with various forms of retinoblastoma (RB) and 5 non-RB patients with constitutional chromosome anomalies involving chromosome 13 were assayed for their clonogenic survival after X-irradiation. Cells from a patient with ataxia telangiectasia (AT) was used as a radiosensitive reference strain. When compared with cell strains from 7 healthy persons as normal controls, a marked radiosensitivity was observed in strain from an AT patient. However, none of the cell strains derived from RB patients or patients with inborn anomalies in chromosome 13 showed pronounced deviation from the normal range of radiosensitivity. The findings thus did not warrant either the RB as radiosensitive genetic disease or the presence of repair locus on chromosome 13, deletion or triplication of which was previously suggested to link to radiosensitivity.

Cell Survival↗
PubMed1982

Possible inactivation of part of chromosome 13 due to 13qXp translocation associated with retinoblastoma.

Chromosome examination of a female patient with 13/X translocation associated with retinoblastoma was carried out using peripheral blood lymphocytes and cultured skin fibroblasts. The constitutional karyotype was 46,X,t(13;X) (q12;p22). Q-banding analysis showed that the translocated chromosomes were of paternal origin. Studies on DNA replication pattern with Giemsa banding using the bromodeoxyuridine substitution technique revealed that the derivative X chromosome was late replicating, and the translocated chromosome 13 was affected by the spreading of lyonization. Such a functional monosomy of 13q14 may also be involved in retinal blasts, and be related to the development of retinoblastoma.

Chromosome Banding↗