Biomedical subjects

Takahiro Kawabe

Publications and source records attributed to Takahiro Kawabe.

4 recordsLinked to original sources

PubMed2005

Mechanism responsible for texture transparency tunes to second-order structures.

This study examined the involvement of second-order processing in the perception of transparency from texture. Stimuli consisted of two superimposed plaid patterns with two diagonal gratings defined by contrast modulation. We investigated the probability of reporting transparency (simultaneous percept of the two gratings) as functions of envelope frequency and either carrier frequency (Experiment 1) or carrier orientation (Experiment 2). Perception of transparency was more often with a large difference in carrier signals between the two gratings. Moreover, a lower envelope frequency was required for the perception of transparency. These results indicate that the mechanism responsible for texture transparency may tune to second-order structures that are differentiated in terms of first-order signals and that decomposition or integration of structures may be determined in terms of the difference of first-order signals between structures.

Contrast Sensitivity↗

PubMed2004

Surface segregation driven by orientation-defined junctions.

This study was designed to ascertain whether the human visual system can segregate overlapped surfaces by integrating texture borders at second-order X-junctions. The stimuli used were crossed vertical and horizontal stripes consisting of Gabor micro-patterns. We manipulated the orientation of the center region of each stripe. Observers judged whether the crossed stripes appeared as "two overlapped stripes" or "five individual regions." The results showed that the probability of perceiving overlapped stripes exceeded the chance level (0.5) when the orientation differences between the center and flanking regions were less than 30 degrees. We suggest that the integration of texture borders along each stripe occurs by the filter-rectify-filter mechanism, resulting in the impression of overlapped surfaces. When this fails, the outcome is the perception of five individual regions.

Humans↗

PubMed2004

Perceptual grouping in shape from shading.

We report on the reversal of asymmetry in visual-search tasks with shaded items. Previous studies have suggested that the target of a bottom-lit disk among distractors of top-lit disks is detected in a rapid and parallel manner, but not vice versa. However, in this study, we have shown that the compound items of top-lit disks were searched more quickly than those composed of bottom-lit disks where the items had to be segregated from their background. By modulating the inter-element distances, we confirmed that the reversal of search asymmetry cannot be due to the grouping of items. Further, we showed that the regions of the top-lit disks were perceived as figure more consistently than those of bottom-lit disks. The results indicate that the boundary assignment to the compound items of the top-lit disks enhances the segregation of search items from the background, and that the search mechanism may access the relatively higher representation that includes figure-ground relations.

Depth Perception↗

PubMed2004

Configuration effects on texture transparency.

This study examined the factors producing the perception of transparency between overlaid regions composed of Gabor micro-patterns as functions of their spatial frequency, separation of overlaid regions, and types of orientation modulation. The results showed that the likelihood of perceiving transparency was high both when (1) the difference in Gabor spatial frequency between regions was large, and (2) the region boundary, which was formed by short-range orientation differences in the Gabor micro-patterns, clearly emerged. We conclude that texture transparency appears to result from an interaction between a boundary-detection mechanism defining the shape of each region and a surface-detection mechanism assigning the boundary.

Form Perception↗