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A Ishiguchi

Publications and source records attributed to A Ishiguchi.

9 recordsLinked to original sources
PubMed2000

[Recovery of 3D structure from motion and its statistical efficiency].

In order to investigate characteristics of the "structure from motion" in noise, we compared performances of recovering a three-dimensional structure from motion (3D condition) with those of recovering a two-dimensional structure (2D condition). In addition, we adopted a statistical efficiency approach to analyze the results. We conducted two experiments where we presented to observers a pair of three dots corresponding to three apexes of triangles rotating around an axis projected onto the fronto-parallel plane. A gaussian noise was added to the area of each triangle for each stimulus frame. Observers were required to discriminate areas of two triangles perceived with moving dots. Main results were as follows: (a) Significant difference was found between the efficiencies for 3D condition and 2D condition. We obtained about 50% or less recovery (i.e., a ratio of the 3D efficiency to the 2D one) in Experiment 2. (b) When we removed the constraints, the human efficiency and the percent recovery decreased dramatically.

Adult↗
PubMed2000

[Statistical efficiency of the object recognition with wire-frame stimuli].

To investigate whether internal object representations in the brain are 2D or 3D, we measured discrimination thresholds and calculated statistical efficiencies in the object recognition task based on the ideal observer analysis. Stimulus images were created by orthographic projection of 3D wire-frame objects on a fronto-parallel plane. The discrimination task with the wire-frame stimuli was performed in the monocular (Experiment 1) and the binocular (Experiment 2) conditions. The results indicate that the subjects' statistical efficiencies relative to the 2D ideal observer exceeded 100%, suggesting that the internal object representations should be 3D. In addition, the results revealed that the object type with high-level symmetry led to better discrimination in both experiments. Furthermore, the interaction between 3D cue values and the object regularity was suggested to cause the viewpoint dependency.

Adult↗
PubMed2000

[Statistical efficiency of depth discrimination in stereoscopically overlapped and step-edge patterns].

We compared observers' statistical efficiencies of depth discrimination for two stereoscopic patterns: an overlapped pattern where two planes are overlapped at different depths, and a step-edge pattern where two planes are arranged side by side. In both patterns, elements in one plane were differentiated from those in the other plane by color (red vs. green) or orientation (45 deg vs. -45 deg). In the experiment, subjects were required to determine which plane was in front when Gaussian disparity noise was added to both of the elements' disparity values. The results showed that efficiencies were the same level for both patterns when the elements were differentiated by color. On the other hand, efficiencies were lower for the overlapped pattern than the step-edge pattern when the elements were differentiated by orientation regardless of the set size of elements. The patterns which we used were so sparse that the differences between the color and orientation conditions should arise from the process after matching.

Color Perception↗
PubMed1999

Does symmetry structure facilitate the depth separation between stereoscopically overlapped dot planes?

In the present study, we dealt with the problem of whether a symmetrical structure can influence the discrimination of the depth separation of overlapped dot planes. We investigated this problem with the use of both direct and indirect methods. In the direct method, we presented three or two overlapped dot planes consisting of symmetrical or random dots. The subjects were required to discriminate three overlapped from two overlapped planes. In the indirect method, the subjects were required to discriminate the depth positions of a target dot (or a pair of dots) that disappeared during stimulus presentation. Our results, obtained in three experiments, showed that the discrimination performance improved and reached a perfect level in the direct method and a modest plateau level in the indirect method with increasing relative disparity between the two outer planes, irrespective of whether the dot pattern had a symmetrical structure or not. These results suggest that a detection process for symmetry structure on a two-dimensional plane in three-dimensional space will not have a direct or an indirect connection (e.g., via a feedback loop) to a process involved in the depth separation.

Adult↗
PubMed1996

[Processing of asymmetrical noise in two- and three-dimensional global symmetry].

We investigated how the visual system processes asymmetrical noise in globally symmetrical patterns, and how much noise the visual system needs to discriminate between the perfectly symmetrical and imperfectly symmetrical patterns. Two experiments were carried out in which subjects were required to discriminate between the above patterns. This task was equivalent to a kind of the visual search task because subjects had to search for some targets asymmetrical dot pairs in two-dimensional (Experiment 1) or in three-dimensional mirror symmetry of dot patterns (Experiment 2). The results showed that the visual system processes noise largely in parallel in the two-dimensional symmetry, but largely in serial in the three-dimensional symmetry. In addition, analyses of the percent correct data suggested that the mechanism involved in detecting both the two- and three-dimensional symmetries in activated even by the patterns with a small amount of noise.

Adult↗
PubMed1996

[Effects of the peripheral vision on visually induced vertigo].

Visually induced vertigo, or motion sickness, is thought to be mainly influenced by motion perception, not by shape perception. We examined this point by comparing the effect of the foveal vision on the visually induced vertigo with that of the peripheral vision. We set up three kinds of display conditions: Foveal vision (F), peripheral vision (P), and foveal + peripheral vision (F + P). Videotaped motion was presented on the display. The results showed that a drifting eye movement was larger after the experiment than before the experiment in the (P) and the (F + P) conditions, but not in the (F) condition. In addition, the mirror drawing was improved only in the (F) condition. Subjective ratings for the vertigo were higher in both the (P) and the (F + P) conditions than in the (F) condition. These results indicate that some visual units concerning low spatial frequencies participate in the visually induced vertigo.

Adult↗
PubMed1990

Perception of structure from two-, four-, or eight-dot oscillatory motion: restoration of rigidity with the aid of structural information.

The motion of two dots corresponding to the two endpoints of an oscillating rigid pendulum produces the perception of an elastic rod, not a rigid one. The possibility that structural information about a rigid object whose motion is simulated plays an important role in the perceptual restoration of the rigidity is examined. Two experiments are reported in which the motion of the endpoints of rigid objects (two endpoints for a rod, four for a sheet, and eight for a board) was displayed. Rigid structure was restored whenever structural information could be used to activate a knowledge data-base on the properties of the objects.

Adult↗