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Biomedical subjects

Y Ejima

Publications and source records attributed to Y Ejima.

At least 55 records · Page 3Linked to original sources
PubMed1997

Retention of local information in generation of subjective contours.

Temporal integration characteristics of subjective contour perception was investigated, using the sequential presentation of two pairs of disks with a sector removed. In the first experiment, by matching the contrast of a "real" stimulus, the perceived contrast of the subjective contours was measured as a function of the stimulus onset asynchrony (SOA) between the two pairs of the disks. With increasing SOA, the perceived contrast decreased gradually and levelled off at the SOA of ca 372 msec (1 SD = 119 msec). In the second experiment, the perceived contrast of the inducing disks was measured as a function of SOA using the matching method. The time limit of the additive effect for the contrast perception of the inducing disks was much shorter than that for subjective contours; the critical SOA was ca 65 msec (1 SD = 36 msec). The remarkable difference of the integration time was explained by a hierarchical process; the local spatial filtering, the retention of local information, and the completion of gaps by multiplicative or AND operation.

Contrast Sensitivity↗
PubMed1997

Dependencies of motion assimilation and motion contrast on spatial properties of stimuli: spatial-frequency nonselective and selective interactions between local motion detectors.

Two sets of experiments were carried out to examine dependencies of two types of induced motion (motion assimilation and motion contrast) on spatial properties of stimuli in terms of spatial-frequency tuning of local motion detectors. In the first set, the magnitudes of motion assimilation and motion contrast for a sinusoidal grating were measured at a function of the spatial frequency of the inducing gratings, with the spatial frequency of the test grating as a parameter. In the second set, the magnitudes were measured as a function of the height of the inducing gratings with the spatial frequencies of the test and the inducing gratings as parameters. For motion assimilation, the magnitude was characterized by a low-pass function of the spatial frequency of the inducing gratings, and the critical height of the inducing gratings, which demarcates the extent of the spatial pooling, varied systematically depending on the spatial frequency of the inducing gratings. For motion contrast, on the other hand, the magnitude was characterized by a hand-pass function, and the critical height depended on the frequency of the test grating. These results suggest that motion assimilation is mediated by the spatial-frequency nonselective interaction between the local detectors, in which the motion signals of the detectors tuned to different spatial frequencies are integrated with each other. Motion contrast is mediated by the spatial-frequency selective interaction, in which the motion signals of the local detectors tuned to the same or similar spatial frequencies are compared and differentiated.

Contrast Sensitivity↗
PubMed1997

Moving stimuli define the shape of stationary chromatic patterns.

A study is reported of phenomena involved in perceptually unified organisation of a stationary chromatic pattern and a moving black outline or dot pattern. When the corners of the outline pattern were temporally oscillated on a stationary chromatic square, the chromatic border appeared to follow the moving outline, as if captured by it. This capture effect was also observed with moving dots: the chromatic border was defined by an imaginary line connecting the moving dots. Both capture effects occur over a region that becomes wider with increasing velocity of the oscillation. These observations suggest that the visual system effectively uses information from moving features to define the shape of overlapping chromatic image regions.

Color Perception↗
PubMed1996

Generation of a panel of radiation-reduced hybrids containing human 11q22-23 fragments bearing a HPRT selective marker: identification of hybrids carrying various subregions around the ataxia-telangiectasia locus.

A human-mouse monochromosomal hybrid that contains a human t(X;11) translocated chromosome carrying pter-->q23 segment of chromosome 11 was used to construct a panel of radiation-reduced hybrids. The hypoxhanthine phosphoribosyltransferase (HPRT) gene located close to the translocation breakpoint was used as a marker to select for the hybrids that preferentially retain the 11q22-23 region. Twenty-three HAT-resistant hybrids were isolated and screened by polymerase chain reaction (PCR) for the retention of 31 loci on 11q22-23 region. Among the 14 hybrids that had breakpoints within the 11q22-23 region, 6 hybrids contained fragments that extend either from centromere or telomere to the 5-Mb region spanned by GRIA4 and FDX, carrying various breakpoints within the region. This subpanel could be a potential resource to analyze the ataxia-telangiectasia disease locus and its neighboring region.

Animals↗
PubMed1995

Effects of luminance contrast and phase difference on motion assimilation for sinusoidal gratings.

When a sinusoidal (test) grating is displaced horizontally by a phase angle of 180 deg in a two-frame apparent motion display, the perceived direction of motion is ambiguous; the test grating appears to move either to the left or to the right (or to both directions). On the other hand, when the test grating is displaced by 180 deg synchronously with the inducing gratings which, presented above and below the test grating, jump unambiguously in one direction (e.g. displaced by 90 deg), the test grating always appears to move in the same direction as the inducing gratings (motion assimilation). In the present study, the effects of luminance contrast and phase difference on motion assimilation were examined. The proportion of perceived direction of motion (left or right) was measured as a function of phase difference between the test grating in the first and the second frame. The magnitude of motion assimilation was evaluated as the change in the phase difference for which the proportions of observers' response were equal (50%) for both directions. The magnitude of motion assimilation increased with increase in the contrast of the inducing gratings or with decrease in the contrast of the test grating. Also, the magnitude increased as the phase difference of the inducing gratings departed from 180 deg. Based on these results, a quantitative formulation between the magnitude of motion assimilation, and the contrast and the phase difference of the stimulus gratings was derived. Further, a model was proposed which explains the stimulus dependences of motion assimilation in terms of response-integration among local motion detectors.

Contrast Sensitivity↗
PubMed1994

Increased UV-induced SCEs but normal repair of DNA damage in p53-deficient mouse cells.

UV-induced sister chromatid exchanges (SCEs) in p53-deficient mouse cells were studied to obtain more evidence regarding the involvement of p53 protein in the DNA repair pathway as a checkpoint protein. After 5 J/m2 UV irradiation, mutant-type homozygous cells for p53-deficiency showed the same number of SCEs as the heterozygous and wild-type homozygous cells. In the heterozygous and wild-type homozygous cells, no further increase of SCEs was observed after 10 J/m2 UV irradiation. In contrast, in mutant-type homozygous cells about twice as many SCEs were induced by 10 J/m2 UV as by 5 J/m2 UV. In mutant-type homozygous cells, fractions of S-phase cells decreased just after 10 J/m2 UV irradiation, but recovered to higher than control levels within a short time, while in heterozygous and wild-type homozygous cells, the decrease in S-phase cells was prolonged by more than 6 hr and no increase above control levels was observed. Although no difference in UV sensitivity and repair of UV-induced DNA damage was found among the 3 genotypes, which were determined by the relative colony-forming ability after UV irradiation and removal of thymine dimers and (6-4) photoproducts from cellular DNA, our data strongly suggest an impaired checkpoint function in p53-deficient cells when DNA is damaged.

Animals↗
PubMed1994

Bone mineral assessment by dual-energy X-ray absorptiometry in patients with coxarthrosis.

Forty patients with unilateral osteoarthritis of the hip were studied with dual energy X-ray absorptiometry to quantify disuse osteopenia in their affected leg by examining the proximal femur and tibia. Bone loss was assessed as a percentage of the contralateral value which compares bone mineral density of the affected and normal sides. The percentage contralateral value in the femoral neck and Ward's triangle was 113% and 118% respectively, while that in the tibia was 75%. Bone loss in the proximal tibia of the affected leg could be of value in assessing gait since it correlates with the gait parameters on the hip rating scale. By contrast, bone mineral increase in the proximal femur and correlates only with the degree of valgus deformity of the femoral neck.

Absorptiometry, Photon↗
PubMed1994

Parental origin of germ-line and somatic mutations in the retinoblastoma gene.

Segregation analysis of polymorphic sites within the retinoblastoma (RB) gene and on chromosome 13, as well as the parental origin of the lost allele in the tumor, were analyzed in 24 families with RB patients. Four mutant alleles transmitted through the germ-line and seven de novo germ-line mutant alleles were identified in 11 patients with hereditary RB. Segregation analysis within the RB gene and on chromosome 13 was useful for DNA diagnosis of susceptibility to RB in relatives of hereditary patients, even if mutations were not identified. All seven de novo germ-line mutant alleles were paternally derived. The bias toward the paternal allele for de novo germ-line mutations of the RB gene was statistically significant. Seven paternal alleles and six maternal alleles were lost in 13 non-hereditary RB tumors with no bias in the parental origin of the somatic allele loss. These results suggest that the physical environment or a deficiency in DNA repair during spermatogenesis may be associated with significant risk factors for de novo germ-line mutations.

Alleles↗
PubMed1993

Loss of heterozygosity on chromosome 13 and its association with delayed growth of retinoblastoma.

Loss of heterozygosity (LOH) on chromosome 13 and the age of patients at operation were studied in 46 cases of retinoblastoma (RB) tumors, of which 25 were hereditary and 21 were non-hereditary. The frequency of LOH was 70% for all informative tumors, but significantly higher in non-hereditary tumors (90%) than in hereditary ones (52%). Our results suggest that LOH might be involved in the initial somatic events in non-hereditary tumors. Age at operation of patients with hereditary tumors was significantly lower than that of patients with non-hereditary tumors. Even when tumors associated with a family history were omitted from among the hereditary cases, the difference was still significant. In the case of hereditary tumors, age at operation of LOH-negative patients was significantly lower than that of LOH-positive patients. When tumors associated with a family history were omitted, the difference was still significant. The delay in development of LOH-positive tumors suggests that LOH for one chromosome 13 may be disadvantageous with respect to growth of RB tumors.

Age Factors↗
PubMed1993

On the loss of apparent motion between isolated chromatic stimuli near isoluminance.

Long range apparent motion (AM) between two isolated stimuli breaks down following prolonged inspection. Time-till-breakdown (TTB) for AM between random-dot squares (red or green) on a red random-dot background was measured as a function of luminance contrast of the stimuli against the background. For the same-color (red squares on the red background) and the different-color (green squares on the red background) conditions, TTB showed clear dependence on the luminance contrast, diminishing with decreasing the contrast. Near isoluminance (luminance contrast of approx. -14 to +14%), AM for the same-color condition disappeared, but AM for the different-color condition was clearly seen and persisted for 7-14 sec. These results show that AM can be produced by color alone. Previous controversial question on the loss of long range AM near isoluminance may be explained by taking into account the contrast dependence of the breakdown effect and the experimental procedures employed.

Color Perception↗
PubMed1992

Spectral sensitivities for illusory contour perception: a manifold linkage of chromatic and achromatic cues with the generation of contours.

Using colored inducing patterns presented as increments upon a white uniform background, the increment thresholds needed for illusory contour perception were measured as a function of the wavelength of inducing pattern. The spectral sensitivity functions were obtained with varying adaptation level and stimulus configuration, high and low background illumination, and line-based and figure-based inducing patterns. The results showed a distinctive feature between the line-based and the figure-based illusory contours. The sensitivity functions for the line-based illusory contours showed the characteristics of non-opponent mechanisms and they were shape invariant with background intensity and spatial variables. On the other hand, the sensitivity functions for the figure-based illusory contours showed non-opponent nature for low background illumination but opponent nature for high background illumination. It is suggested that the generation of illusory contours involves concurrent processing of different cues of luminance and color, and that photopic adaptation level and stimulus configuration control the degree of the contributions of chromatic and achromatic mechanisms to contour formation.

Adaptation, Ocular↗
PubMed1992

Inhibitory interaction in a split/fusion apparent motion: lack of spatial-frequency selectivity.

Spatial-frequency selectivity of apparent motion (AM) between isolated Gabor patches was examined under two- and three-patch conditions. In the two-patch condition, the likelihood of seeing AM between two Gabor patches was measured with varying frequency difference between the patches. In the three-patch (split/fusion) condition, the likelihood of AM between target patches of the same frequency was measured as a function of the frequency of the inhibiting patch. AM perception in the two-patch condition deteriorated with increasing frequency difference, showing symmetrical spatial-frequency selectivity. On the other hand, the inhibition of AM in the three-patch condition was frequency asymmetric; when the frequency of the inhibiting patch was higher than that of the target patches, the magnitude of inhibition decreased with increasing the frequency of the inhibiting patch. When the frequency of the inhibiting patch was lower, the magnitude of inhibition remained almost constant regardless of the frequency difference between the inhibiting and target patches.

Contrast Sensitivity↗
PubMed1992

Induction of chromosome aberrations by monochromatic X-rays with resonance energy of phosphorus K-shell absorption edge.

The induction of chromosome aberrations by monochromatic soft X-rays with energies corresponding to the K-shell absorption edge of phosphorus has been studied in density-inhibited mouse m5S cells. The frequency of dicentrics was markedly enhanced when the cells were irradiated with energy at the K-shell resonance peak (2.153 keV) as compared to those at below (2.146 keV) or above (2.160 keV) the peak. The quantum efficiency was calculated to be 2.7 x 10(-3) for the induction of dicentrics per photoelectric absorption of phosphorus atom in DNA, which was comparable to the known efficiencies of X- or gamma-ray-induced DNA double-strand breaks. However, comparison of the efficiencies based on the absorbed dose indicated that the magnitude of the enhancement was not due solely to the selective photoelectric absorption of the phosphorus atoms in DNA, and suggested the combined contributions of Auger electrons from phosphorus atoms within and outside the DNA molecules.

Animals↗
PubMed1991

Contribution of transient and sustained responses to the perception of apparent motion.

The likelihood of seeing apparent motion (AM) was measured as a function of inter-stimulus-interval (ISI) between two isolated Gabor patches separated by 4 deg with spatial frequency (0.75, 2.0 and 4.5 c/deg) and exposure duration (33 and 1000 msec) as parameters. For the short stimuli, the likelihood of AM for the low-spatial-frequency of 0.75 c/deg was higher than that for the high-spatial-frequency of 4.5 c/deg, but for the long stimuli, the former was similar to, or lower than the latter. Decreasing the mean luminance from 190 to 0.8 cd/m2 impaired AM for the short stimuli of 2.0 c/deg, but improved AM for the long stimuli. The dependencies of AM on spatial frequency, exposure duration and adaptation level may be ascribed to the changing contribution of the transient and the sustained responses.

Adaptation, Ocular↗
PubMed1991

Somatic and germinal mutations of tumor-suppressor genes in the development of cancer.

It is generally thought that the germinal mutation of tumor-suppressor genes predisposes the affected children to the development of certain types of hereditary tumors while the somatic mutation of the same genes links to the development of non-hereditary tumors. Retinoblastoma susceptibility gene (RB gene) is a prototype of such genes. We studied the parental origin of new mutation of the RB gene in the sporadic hereditary and non-hereditary retinoblastoma and osteosarcoma. The results showed a preferential involvement of parental genome in the new germinal as well as initial somatic mutations. The male-directed mutagenesis even in the somatic cells has been implicated as a reflection of germinal origin of mutation, even for non-hereditary tumors as a manifestation of mutational mosaicism associated with delayed mutation. The importance of the new mutations occurring as mosaics should be emphasized in the evaluation of cancer risks from parental exposures to radiation and chemicals.

Genes, Retinoblastoma↗
PubMed1990

Establishment of a novel immortalized cell line from ataxia telangiectasia fibroblasts and its use for the chromosomal assignment of radiosensitivity gene.

An immortalized cell line was established from a female ataxia telangiectasia (AT) patient by the transfection of primary skin fibroblasts with origin-defective SV40 DNA. The cell line was characterized by a hypodiploid chromosome constitution and radiation hypersensitivity. The established cell line was used as a recipient for microcell-mediated chromosome transfer. Among seven G418-resistant clones obtained by the fusion with microcells from mouse A9 cells carrying a pSV2neo-tagged normal human chromosome 11, three clones showed restoration of radiation resistance with concomitant gain of an extra intact chromosome 11, while the others contained no recognizable or deleted chromosome 11. The association of the presence of 11q14----qter region with the radioresistance suggests the presence of AT gene in this chromosomal region.

Ataxia Telangiectasia↗
PubMed1989

Induction of chromosome aberrations in human lymphocytes by monochromatic X-rays of quantum energy between 4.8 and 14.6 keV.

The induction of chromosome aberrations was studied in human peripheral blood lymphocytes irradiated in vitro with synchrotron-produced monochromatic soft X-rays of quantum energy in a range between 4.8 and 14.6 keV. These X-rays were more effective in producing chromosome aberrations (dicentrics and rings) than 60Co gamma-rays. The efficiency increased with increasing LET of the photoelectrons and their associated Auger electrons, reaching a maximum at a track average LET (L delta = 100, T) of around 4 keV/microns, and tended to decrease or become rather refractory with further increase of LET. This unique LET dependency was consistent with the dual nature of chromosome aberration formation, and interpreted as a reflection of a limited range of photoelectrons as compared with the size and intranuclear geometry of the elemental chromatin fibres as vehicles of damage interaction.

Chromosome Aberrations↗