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Biomedical subjects

K Toyama

Publications and source records attributed to K Toyama.

At least 433 records · Page 24Linked to original sources
PubMed1987

Preservation of position and motion stereopsis in strabismic subjects.

Preservation of position (PS) and motion stereopsis (MS) of strabismic subjects in central and peripheral visual fields (N = 51) was studied in relationship with various strabismic parameters and aspects: present and past squint angles, age at the time of strabismic appearance and the first treatment, present visual acuities, and present and past strabismic polarity (convergent or divergent). The present squint angle was the only major parameter relevant for the preservation of PS and MS. The critical squint angle for the preservation was virtually null for central MS (it was present in 12 of the 16 subjects with squint angles smaller than the critical value), 2 degrees for central PS (17/18), 5 degrees for peripheral PS (23/28), and 10 degrees for peripheral MS (37/42). These findings indicate the importance of correction of visual axes in the preservation of stereopsis. The finding that the central and peripheral types of PS and MS could occur independently in strabismic subjects also suggests that they are based on different neural mechanisms.

Adolescent↗
PubMed1986

The responsiveness of Clare-Bishop neurons to motion cues for motion stereopsis.

Under paralysis of eye movement and optical adjustment of visual axes of the two eyes, neuronal responsiveness in cat Clare-Bishop (CB) cortex to the binocular presentation of visual stimuli was studied using two types of visual stimulator which presented: 3-dimensional motion of a visual stimulus; and the motion cues (movement of retinal images in the two eyes) contained in the 3-dimensional motion. On the basis of the responsiveness to 3-dimensional motion presented by the first type of stimulator, the CB cells were classified into approaching (AP) cells which were selectively responsive to the approaching motion of a visual stimulus, recessive (RC) cells responsive to the recessive motion, frontoparallel (FP) cells responsive to the frontoparallel motion and non-selective (NS) cells responsive to more than two types of motion. The investigation of the CB cells with 2-dimensional motion stimulus demonstrated 3 different types of binocular interaction: facilitatory (52/239); antagonistic (33/239) or linear summation (154/239). Cells exhibiting the facilitatory interaction (n = 52) were all FP cells, those exhibiting the antagonistic interaction were either AP (n = 25) or RC cells (n = 8), and those exhibiting the linear summation were comprised of all varieties of cells (49 AP, 17 RC, 31 FP and 57 NS cells). The cells responsive to the approaching (37 AP cells) or recessive motion between the center of the receptive area and the nose (10 RC cells), or frontoparallel motion (42 FP cells) in the horizontal direction exhibited the selective responsiveness to the motion disparity (a combination of horizontal movement of retinal images in the two eyes), and those responsive to the vertically or obliquely deviating approaching (20 AP cells) or recessive motion (14 RC cells), or frontoparallel motion in the vertical or oblique directions (13 FP cells) exhibited that for a combination of the motion disparity and the frontoparallel motion in the vertical or oblique direction. These findings indicate that the CB cell responsiveness to 3-dimensional motion of a visual stimulus is explained by the binocular integration of motion signal viewed by each eye.

Action Potentials↗
PubMed1986

The responsiveness of Clare-Bishop neurons to size cues for motion stereopsis.

The responsiveness to the size cue, and a combination of the size and motion cues contained in 3-dimensional motion of a visual stimulus was studied in 118 Clare-Bishop (CB) cells, including 37 and 10 cells selectively responsive to approaching (AP) and to recessive motion along the axis through the center of the receptive area and the nose (RC), 40 cells responsive to the frontoparallel motion in the horizontal direction (FP), 23 cells rather non-selectively responsive to the two types of motion (NS) and 8 cells responsive to the size cue but unresponsive to the 3-dimensional motion (SZ). About three quarters of the AP cells (27/37) were responsive to both an increase in the stimulus size and divergent motion of the retinal images in the two eyes, which represents the size and motion cues for the approaching motion along the axis through the center of the receptive area and the nose, and were optimally excited by a combination of the two visual cues. About the same fraction of the RC cells (6/10) was responsive to the motion (convergent motion) and size cues (a decrease in stimulus size), and optimally excited by a combination of the two visual cues. In contrast, only a small fraction of the FP cells (6/40) were sensitive to the size cue, and all FP cells were optimally excited by the single presentation of the motion cue for the frontoparallel motion (either right- or leftward motion in both eyes). Responses were frequently (18/40) smaller for the combined presentation of the two visual cues than for the single presentation of the motion cue. Similarly, a small fraction of the NS cells (7/23) was sensitive to the size cue, but many of them (16/23) were non-selectively responsive to the size cues for the approaching and recessive motion. A similar study in an additional 108 (78 AP and 30 RC) cells which were responsive to approaching or recessive motion vertically or obliquely deviating from the axis through the center of the receptive area and the nose demonstrated that they were also sensitive to both motion and size cues for that approaching or recessive motion, and were optimally excited by a combination of the two visual cues. These findings indicate that the CB cell responsiveness to 3-dimensional motion is based on the integration of the motion and size signals conveyed through the two eyes. A model of neuronal circuitry was constructed to explain the CB cell responsiveness to the motion and size signals.

Action Potentials↗