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Y Ejima

Publications and source records attributed to Y Ejima.

At least 73 records · Page 4Linked to original sources
PubMed1989

Analysis of simple reaction time to a sinusoidal grating by means of a linear filter model of the detection process.

Simple reaction time (RT) to a sinusoidal grating was analyzed in terms of a linear filter model of the detection process. First, RT contrast functions were determined over a wide range of spatial frequencies and retinal illuminances. Second, calculating the time course of the linear filter's response, theoretical visual latency contrast functions were derived for the same conditions of spatial frequency and retinal illuminance as those in the RT measurements. Comparison of the two functions showed that the contrast dependence of the RT functions was much larger than that of the visual latency functions. The discrepancy between the two functions was satisfactorily described as a power function of the slope of the filter's response at threshold level. On the basis of these results, we propose a model of the RT process. According to the model, the RT process is mediated by a cascade that consists of a level detector, which includes a linear filter followed by a threshold device, and a differentiator of the filter's response.

Attention↗
PubMed1989

[Recessive oncogene and loss of heterozygosity].

Recessive oncogene, which has been originally proposed for the retinoblastoma susceptibility gene, is linked to the development of cancer by missing its gene function followed by the loss of normal allele (often observed as a loss of heterozygosity of neighbouring heteromorphic loci). Recent studies on the loss of heterozygosity in cancers indicate that mutations of such genes are relatively common in human cancers, and play a significant role in the dedifferentiation, progression and evolution of cancers as well as the initiative role. Such initiative and cooperative role of recessive oncogene opened a new field relating to the research on the genetic origin of cancer, evolutional implications of cancer development, and molecular diagnosis for cancer prognosis.

Chromosome Deletion↗
PubMed1988

Types, rates, origin and expressivity of chromosome mutations involving 13q14 in retinoblastoma patients.

A cytogenetic survey of 200 retinoblastoma (Rb) patients revealed that approximately 8.5% of the fresh germinal mutations were microscopically detectable chromosome mutations, either interstitial deletions or rearrangements, involving 13q14. They showed a strong bias toward paternal origin, indicating a significant contribution of errors in paternal meiotic processes. The incidence of patients with Rb due to such chromosome mutations was estimated to be 1.9 x 10(-6) of live births. Age-specific incidence of Rb tumors suggested that the Rb mutations by such chromosomal mechanisms had a lower carcinogenic potential, as indicated by the later onset of disease, than other Rb mutations of germinal origin.

Age Factors↗
PubMed1988

Illusory contours induced by isoluminant chromatic patterns.

An illusory-contour was induced by abutting colored gratings embedded in the white field under isoluminance condition. The present study specified the stimulus conditions that invoked the just-perceptible illusory contours for the isoluminant chromatic patterns. The results showed that the purity difference between the colored lines and the white field required for the illusory-contour perception gave a function closely resembling in shape the function obtained for saturation discrimination. Increasing the width of lines reduced threshold for the perception of illusory contours, while the line spacing had no significant effect. The dependence of the illusory-contour perception upon saturation could be accounted for by considering the extraction of the edge and colour information by means of the opponent-color processes observed for the cells in the retina and LGN. On the other hand, the effects of the spatial parameters met the response properties observed for the cells in the visual cortex. It is suggested that the perception of illusory contour may result from hierarchical organization from the retina to cortex in the visual system.

Color Perception↗
PubMed1988

Positive colored afterimages from the figure-ground configurations of colored lights: effects of chromaticity, luminance and a spatial parameter of the adapting stimuli.

Colored afterimages were obtained after the eye was exposed to the adapting field consisting of the figure-ground configuration of colored lights with the same hue and different saturation. When a colored patch was surrounded by a more saturated field, the color of the afterimage was similar to that of the previous patch (positive afterimage). By measuring the threshold chromaticity difference between the patch and the surround for the production of the positive afterimage, the effects of the chromaticity, luminance and a spatial parameter of the adapting field were determined. The obtained threshold chromaticity differences increased with an increase in the saturation of the adapting field, and with a decrease in the surround luminance. When the adapting field consisted of an equiluminous saturation-modulated rectangular grating, the threshold chromaticity difference curves showed similar properties as those of the contrast thresholds for equiluminous chromaticity-modulated gratings. The results suggest the existence of a set of mechanisms at higher-order level in the visual system, tuning the difference in hue and/or saturation across contours.

Adaptation, Ocular↗
PubMed1988

Increase in copy number of N-myc in retinoblastomas in comparison with chromosome abnormality.

N-myc oncogene amplification was studied in tumor tissue DNA from Japanese retinoblastoma patients, taking into consideration their uni- or bilateral disease form, their family history, and any chromosome abnormalities. Of the 23 cases examined, seven (30%) showed a 1.9- to 2.3-fold amplification of N-myc. No correlation was found between N-myc amplification and either tumor form or family history. Two of three cases having double minute bodies in their tumors showed N-myc amplification. In two tumors with 13q deletions, one produced in the host with constitutional 13q--abnormality showed no N-myc amplification, and the other one produced in the host with normal karyotype showed an N-myc amplification. These results indicate N-myc amplification is independent of the known genetic background in retinoblastoma patients.

Child↗
PubMed1988

Temporal integration of stimulus increments under chromatic adaptation: effects of adaptation level, wavelength, and target size.

The threshold-duration functions were determined for a 520-, 570-, or 650-nm test presented upon the various monochromatic backgrounds. The variation of the threshold-duration functions with the background intensity, taken with the 520- or 650-nm test, showed a strong dependence on the background wavelength. This wavelength difference became prominent for the high background intensities: for the bright 570-nm background, partial summation occurred for the duration range from 50 to 200 msec, while such a partial summation effect was very small for the bright 520- and 650-nm background. Test for test-mixture additivity indicated that the longer integration time, obtained for the 520- or 650-nm test with the 570-nm background, was attributed to contribution of the opponent-color process. The elongation of the temporal integration period was found to be affected by the size of the test target. The interrelation among temporal and spatial summation, background intensity, and wavelength could be accounted for by temporal integration of the opponent-color process in addition to that of the cone mechanisms.

Adaptation, Ocular↗
PubMed1987

Chromosome aberration frequency and radiation dose to lymphocytes by alpha-particles from internal deposit of Thorotrast.

Frequencies of chromosome aberrations in peripheral blood lymphocytes from 63 Thorotrast patients were analysed basing on the age distribution of lymphocytes. The frequency and distribution of chromosome aberrations among lymphocytes are best explained if we assume that the lymphocytes are renewed as an exponential function of time and spend most of their lifetime in the distributive pool where, while exchange of lymphocytes is taking place, the lymphocytes are hit by alpha-particles from Thorotrast aggregates resulting in the formation of chromosome aberrations and killing at specific rates per hit. The model predicts that the aberration frequency is rather insensitive to the fluence rate because of modulation by cell killing by hit. Fitting the observed data to the model showed that approximately 0.8 dicentrics and rings were produced by a single path of alpha-particle and average fluence rate to lymphocytes in a group of patients with the highest aberration frequency was estimated to be about 1.5 hits or 87 rad/lymphocyte/year.

Aged↗
PubMed1987

Effect of surround configuration on increment thresholds of a tiny violet flash.

Increment thresholds were measured for a 5', 435-nm test flash (50 or 200 msec) on background fields of various wavelengths and spatial configurations. As the field diameter was increased, the detection threshold for the 50-msec test decreased rapidly and leveled off when the field diameter exceeded 20'. For short-to-middle wavelength fields (much less than or equal to 503 nm), the detection threshold for the 200-msec test varied with field diameter in a similar manner to those observed for the 50-msec tests, while for middle-to-long wavelength fields (much greater than or equal to 544 nm), the detection threshold continued to decrease even when the field diameter exceeded 20'. The temporal-integration properties and the threshold vs intensity curves were determined for 465-nm and 579-nm fields to specify the mechanisms responsible for the detection. It was shown that the detection thresholds of the test upon the large 579-nm field were characterized by the short-wavelength mechanism isolated by an intense yellow adapting field, whereas the detection thresholds of the test upon the small 579-nm or the 465-nm field showed an intrusion of a more sensitive alternate mechanism, presumably the middle-wavelength mechanism. It was suggested that the sensitivity of the S cone signals might be affected by spatially distributed signals from the longer-wavelength mechanisms.

Adaptation, Ocular↗
PubMed1987

Simple reaction time to sinusoidal grating and perceptual integration time: contributions of perceptual and response processes.

For sinusoidal gratings, two experiments were carried out to examine relation between simple reaction time and perceptual and response processes. First, the simple reaction time (RT) was measured as a function of grating contrast with spatial frequency as a parameter. Second, contrast threshold was determined as a function of exposure duration (ED). On the basis of the RT-contrast function and the ED-contrast threshold function empirically obtained, the difference between the RT and the ED was evaluated as a function of grating contrast. The RT-ED difference, in which the perceptual integration time was eliminated, was considered to reflect the transmission time, delay in the response process, and delay in the motor response. As the grating contrast increased, the RT-ED difference decreased rapidly at first, and then gradually, and finally leveled off. The RT-ED difference vs contrast function depended on spatial frequency. Based on the analysis of the characteristics of the RT-ED functions, the effects of grating contrast and spatial frequency on the simple RT could be ascribed to the changing contributions of the perceptual and the response processes.

Evoked Potentials, Visual↗
PubMed1986

Ataxia telangiectasia with generalized skin pigmentation and early death.

A female infant with clinical and laboratory features of ataxia telangiectasia (AT) showed two clinical features exceptional for the disease, i.e. generalized skin pigmentation and an unusually early death at the age of 15 months. Her clinical features supportive of the diagnosis of AT included growth and developmental retardation and muscle weakness. Findings indicating immunodeficiency included recurrent pulmonary infections, failure of PHA stimulation of PB lymphocytes, decreased levels of serum IgM and IgA and on autopsy, an atrophic thymus without Hassall's corpuscles. Her cultured skin fibroblasts showed increased spontaneous chromosome breakages and hypersensitivity to X-ray irradiation, as would be expected for AT fibroblasts. She showed elevated blood HbF levels, macrocytic anaemia, granulocytopenia and thrombocytopenia, findings suggestive of a preleukaemic or leukaemic process. Yet aspirates of her bone marrow revealed no malignant cells. Autopsy revealed bilateral Pneumocystis carinii pneumonia, telangiectatic lesions in all the internal organs studied, sparse and degenerative Purkinje cells in the cerebellar cortex and atrophic ovaries. In view of these findings, it was concluded that the patient had a hitherto undescribed variant of ataxia telangiectasia.

Ataxia Telangiectasia↗
PubMed1986

Spatial and chromatic antagonism between the long- and middle-wavelength cones in the detection of long-wavelength flashes.

Field additivity was tested for small red increments on small and large adapting fields. The results for a large adapting field showed the failure of field additivity of the cancellation type, providing strong evidence for cone-antagonistic coding, while the results for a small adapting field showed field additivity. The cancellation effect took place concurrently with the spatial sensitization effect, thus suggesting that the spatial and chromatic antagonism occur concomitantly at some stage in the detection pathway.

Color Perception↗
PubMed1986

Increment spectral sensitivities for spatial periodic grating patterns: evidence for variable tuning of the chromatic system.

Increment spectral sensitivities were measured for spatial periodic grating patterns. First, the increment threshold was determined as a function of wavelength, for various spatial frequencies and white-background intensities. Second, the additivity of test mixture was tested. Thirdly, the threshold vs intensity curves were determined for various spatial frequencies of test monochromatic stimuli. Finally, the increment threshold was determined as a function of spatial frequency. The following results were obtained: the background intensity and the spatial frequency affected the increment spectral sensitivity functions in different manners; the result of test mixture showed subadditivity for high background intensity and approximately linear additivity for low background intensity; the resultant t.v.i. curves converged toward Weber's law at high background intensity; and the sensitivity vs spatial frequency curve showed a loss of the sensitivity at low spatial frequency for high background intensity. These results called in question the existing hypothesis of separate chromatic and achromatic systems whose spectral tunings are invariant with a spatial parameter, but favored the hypothesis of variable tuning of the chromatic system.

Color Perception↗
PubMed1985

Interaction between short- and longer-wavelength cones in hue cancellation codes: nonlinearities of hue cancellation as a function of stimulus intensity.

Hue cancellation experiments were carried out to test the linear additivity of chromatic valences. There were two kinds of experiments: the measurements of the yellow-blue cancellation function and of the red-green one. The opponent-color equilibria were determined as a function of stimulus intensity for mixture lights of various spectral compositions. The results of the yellow-blue cancellation functions showed that the nonlinearity of the cancellation code strongly depended on the spectral compositions of stimuli: the nonlinearity became evident under conditions producing a relative increase in the long-wavelength-cone excitation, while it was reduced under conditions producing a relative increase in the middle-wavelength-cone excitation. This property could be well explained if we assume that the gain of the short-wavelength signal might be controlled by a difference signal between the long- and middle-wavelength cones. The results of the red-green cancellation functions showed that the cancellation function for a violet light was nonlinear under some specific conditions, while the cancellation function for a red light remained linear. The nonlinearity of the short-wavelength red response became more prominent under conditions producing a relative increase in the long-wavelength-cone excitation. It is suggested that the cone-interaction between the short- and longer-wavelength cones may be responsible for the nonlinearities of the yellow-blue and red-green hue cancellation codes.

Adaptation, Ocular↗
PubMed1985

Apparent contrast of a sinusoidal grating in the simultaneous presence of peripheral gratings.

Apparent contrast of a vertical sinusoidal grating in the simultaneous presence of peripheral gratings was measured as a function of peripheral contrast, with test contrast, and relative phase and position of the two gratings as parameters. When the peripheral gratings were horizontally adjacent to the test grating, irrespective of the phase relation, the apparent contrast was raised in the range of peripheral contrast below the test contrast, but depressed in the range of peripheral contrast above the test contrast. When the peripheral gratings were vertically adjacent to the test grating, a similar tendency as mentioned above was observed under the in-phase condition. Under the opposite-phase condition, the apparent contrast was raised monotonically with an increase in peripheral contrast. These effects can be explained in terms of three processes of brightness induction, spatial summation and interaction between the spatial-frequency selective mechanisms.

Adaptation, Ocular↗
PubMed1985

Effects on grating detection of vertically displaced peripheral gratings.

Contrast threshold for a sinusoidal target in the simultaneous presence of the vertically displaced peripheral gratings was measured as a function of the peripheral contrast and the separation. When the signal and peripheral gratings were in phase, the low-contrast peripheral gratings produced the improvement in signal threshold, while the high-contrast gratings produced threshold elevation. The facilitation effect was extended to the separation equating to 10 grating cycles, whereas the inhibition effect was restricted to the region near the border. When the two gratings were out of phase, the low-contrast peripheral gratings produced threshold elevation, while the high-contrast gratings exerted little effect on signal threshold. The results were explained in terms of spatial summation and lateral inhibition.

Female↗
PubMed1985

Red-green opponency in the detection and the perceptual hue cancellation.

We show how the red-green antagonism in the detection process is related to the red-green antagonism in the hue cancellation. By measuring the incremental redness or greenness thresholds for bichromatic mixtures, the red-green antagonism was determined at color threshold and in the perceptual hue cancellation. By measuring the detection threshold for bichromatic mixtures, the red-green antagonism was determined at detection threshold. There was agreement among the red-green antagonisms at detection threshold, at color threshold and in the perceptual hue cancellation.

Adaptation, Ocular↗