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Biomedical subjects

S Shimojo

Publications and source records attributed to S Shimojo.

At least 37 records · Page 2Linked to original sources
PubMed1988

[Xenon CT CBF mapping derived from two minutes inhalation].

Although xenon enhanced CT method for local cerebral blood flow measurement has been brought into a clinical practice, the technique has inherent limitations including anesthetic effects and expensive cost of xenon by a large consumption. To overcome these problems a modified method with a short-duration inhalation was developed and its validity was attested. Siemens Somatom SF with a resolution of 256 X 256 pixels and a scan time of 10 seconds was used. The subjects inhaled 50% Xe/O2 gas mixture from an apparatus consisted of Douglas bag and an open circuit. Xenon concentration in the expired gas was continuously monitored and estimated for arterial blood concentration by using a hematocrit correction. PaCO2 was monitored throughout the study. At the starting point and the endpoint of the inhalation two scans were performed respectively. Thus obtained four images were processed for CT noise cancellation, summation and subtraction to produce an in vivo autoradiography image. Local CBF was calculated from equations derived from the autoradiographic technique with a fixed partition coefficient of lambda = 1. Computer simulation studies were performed to find the optimal scan point to obtain an autoradiographic image and to estimate the calculation errors of this method. One minute and forty-five seconds was found to be the optimal scan point to gain an autoradiographic image in view of a balance between linearity of CBF/enhancement curve and total amount of tissue enhancement. The theoretical errors due to the assumption for a fixed partition coefficient were calculated to be 8% underestimation for gray matter and 5% overestimation for white matter.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1987

Vernier acuity is less than grating acuity in 2- and 3-month-olds.

Vernier acuity and grating acuity were measured longitudinally starting at 1 or 2 months of age in 22 infants, using a two-alternative, forced-choice preferential looking technique. For vernier acuity, the motion-sound display was employed. For grating acuity, a preferential looking method was employed. Steps of the stimulus (vernier offset and spatial frequency of the grating) and procedures were basically identical between the two acuity tests. The range of stimuli was set so as to compare the two acuities at younger ages. Results show: vernier acuity is less than grating acuity at 11-12 weeks of age or younger, and the developmental rate of vernier acuity is greater than that of grating acuity in the first half-year of life. To interpret the data, it was speculated that: the mean sampling distance (center-to-center distance between receptive fields) may influence vernier acuity more than grating acuity, whereas the size of the receptive field may influence grating acuity more than vernier acuity: when the mean sampling distance is large relative to the size of the receptive field, vernier acuity may be less than grating acuity. Thus, the neonatal visual system, just as the visual system in the periphery and in strabismic amblyopia, may be characterized by spatial undersampling.

Age Factors↗
PubMed1987

Perceived spatial organization of cutaneous patterns on surfaces of the human body in various positions.

The perceived spatial organization of cutaneous patterns was examined in three experiments. People identified letters or numbers traced on surfaces of their body when the relative spatial orientations and positions of the body surfaces and of the stimuli were varied. Stimuli on the front or back of the head were perceived with respect to a frame of reference positioned behind those surfaces, independent of the surfaces' position and orientation. This independence may relate to the way in which the sensory apparatus on the front of the head is used in planning action. Stimuli on other surfaces of the head and body were perceived in relation to the position and orientation of the surface with respect to the whole body or trunk (most of which was usually upright). Stimuli on all transverse/horizontal surfaces were perceived with respect to frames of reference associated with the head/upper chest area. These frames were also used for stimuli on frontoparallel surfaces in front of the upper body. These observations may result from the use of "central" frames of reference that are independent of the head and are associated with the upper body. Stimuli on surfaces in other positions and orientations (with two exceptions) were perceived "externally"--that is, in frames of reference directly facing the stimulated surface. The spatial information processing we found may be fairly general because several of our main findings were also observed in very young children and blind adults and in paradigms studying perception by "active touch" and the spatial organization of the motor production of patterns.

Humans↗
PubMed1987

Attention-dependent visual capture in double vision.

When the visual image of a body part, such as a finger, is doubled by a prism, the 'felt' position of that body part is captured by one of its visual images. Moving eye fixation from one to the other visual image is accompanied by a quick shift of the felt position. When focal attention is dissociated from foveation, the former determines visual capture. These new observations underline an active role of focal attention in intersensory integration and sensory-motor coordination of body parts.

Attention↗
PubMed1986

Pre-stereoptic binocular vision in infants.

In a preferential looking experiment, identical patterns (vertical stripes) were presented to both eyes on one of two screens while orthogonal patterns (vertical stripes in one eye and horizontal stripes in the other) were presented on the other screen. Most infants younger than 3.5 months of age originally showed a preference for the dichoptic (interocularly orthogonal) pattern. At an average age of 3.5 months, however, they showed a sudden shift of preference from this pattern to the interocularly identical pattern. The full shift from a preference for one stimulus to the other (both statistically significant) occurred within a few weeks in most cases. The onset age of the shift in preference agreed with the onset age of fusion-rivalry discrimination found in a previous study (Birch et al., 1985). The original preference for the bincularly orthogonal patterns may be interpreted as a preference for a grid (interocularly emergent intersections) over a grating, judging from results of two control experiments. These data suggest that the pre-stereoptic system non-selectively combines information from the two eyes without regard to edge orientation because it loses eye-of-origin information at a relatively early stage of binocular visual processing. Thus, the pre-stereoptic system does not have the capability of interocular suppression. The theoretical and clinical significance of the new findings are discussed along with a neuronal model of cortical development of ocular segregation and binocular pathways.

Adult↗
PubMed1986

Congenital myopic esotropia: a case study.

A congenital myope developed a 20 delta left esotropia at 8 months of age. His eyes aligned immediately with a -4.00 D correction and would become esotropic when the glasses were removed. Before eyeglass wear best corrected acuity was reduced for both eyes with the left eye acuity significantly lower than the right. From age 8 to 12 months with part-time eyeglass wear, acuity improved and became equal for the two eyes. At 12 months of age the eyeglasses were lost and within 1 month the strabismus no longer responded to minus lenses and amblyopia reappeared in the left eye. This indicates that a myopic infant may stop bifixating blurred images beyond his far point and then cease to be able to relax convergence thereafter. It has the broader implication that tonic vergence posture and AC/A ratio may develop according to the visual experience of each infant.

Esotropia↗
PubMed1985

Preferential-looking assessment of fusion and stereopsis in infants aged 1-6 months.

The ability of infants to discriminate zero-disparity stimuli from both reverse contrast (rivalrous) and disparate (stereoscopic) stimuli was investigated in a two-alternative, forced-choice, preferential-looking paradigm. Few infants under 4 months of age demonstrated discrimination for any stimulus pairing. Of the infants tested at 4 months of age, approximately 70% preferred zero-disparity stimuli to reverse contrast stimuli, and 82% preferred stereoscopic stimuli to zero-disparity stimuli. Nearly 100% of 5- and 6-month-old infants exhibited these preferences. These findings suggest that sensory fusion is not present at birth but develops rapidly over the first 6 months of life. The time course for the development of sensory fusion was similar to the time course for the development of stereopsis in nine infants tested longitudinally.

Adult↗
PubMed1979

Electromyographic study of patients with dysfunction of the Eustachian tube.

In order to determine how often dysfunction of the tube might arise from dysfunction of the tubal muscles, electromyographic examination of the muscles was carried out on 34 patients with occluded or patent tube. Using a monopolar needle electrode inserted through the nose, selective EMG of the tensor and levator veli palatini muscles were picked up during swallowing. It was found that the patients showed neither abnormally reduced nor increased muscle activity. Comparison of muscle activity of the normal tube and of both the occluded and patent tube revealed no significant differences. Therefore, myogenic cause of tubal dysfunction seems improbable from the clinical viewpoint.

Electromyography↗