Biomedical subjects

Sang Wook Hong

Publications and source records attributed to Sang Wook Hong.

3 recordsLinked to original sources

PubMed2004

Brightness contrast and assimilation from patterned inducing backgrounds.

Theories of induction propose that the brightness of a test patch within a complex surround is explained by local contrast or by integrating contrasts from various regions within the surround, weighted inversely with the distance from the test. Results here corroborate that brightness induction from a patterned background depends on both contiguous and non-contiguous surrounding light, but the measurements were inconsistent with any linear integration of contrast at edges within the scene. In some conditions, assimilation rather than contrast to contiguous surrounding light was observed, depending on the luminance of the light in non-contiguous regions. This finding implies that brightness induction from patterned backgrounds depends on neural processes that can cause contrast and/or assimilation, depending on the luminance relation between contiguous and non-contiguous regions. A model in the literature postulating that the influence of a non-contiguous edge is regulated by the amount of contrast at the contiguous edge can accommodate brightness induced by these patterned backgrounds.

Adaptation, Ocular↗

PubMedDate not supplied

Brightness induction: unequal spatial integration with increments and decrements.

Modern theories of brightness induction include an influence from regions that do not share a border with the target. This study tested whether the spatial range of neural integration is the same with incremental versus decremental contrast edges in relatively remote parts of the background. Using an asymmetric matching task, observers set the brightness of a comparison ring, within its own uniform surround, to match the brightness of a test ring within a contiguous surround and a noncontiguous background. The measurements showed that the area of integration depended on the incremental versus decremental contrast polarity at the edge between the surround and background. This implies that brightness induction from an inhomogeneous background must consider the polarity of contrast edges within the whole scene.

Adaptation, Ocular↗

PubMedDate not supplied

Resolution of binocular rivalry: Perceptual misbinding of color.

Is neural binding of color and form required for perception of a unified colored object? Individual cells selectively tuned to both color and orientation are proposed to moot the binding problem. This study reveals perceptual misbinding of color, thereby revealing separate neural representations of color and form followed by a subsequent binding process. Low luminance-contrast, rivalrous chromatic gratings were presented dichoptically. Each grating had alternating chromatic and gray stripes (e.g., red/gray in the left eye, green/gray in the right eye). Observers viewed the two rivalrous, 2 cpd gratings for 1 min. The duration of exclusive visibility was measured for four percepts: left-eye stimulus, right-eye stimulus, fusion of the two colors, or a two-color grating (e.g. a red/green grating). The percept of a two-color grating (misbinding) was observed with Michelson luminance contrast in the grating up to 20%. In general, for a given level of luminance contrast either misbinding (low luminance contrast) or color mixture (high luminance contrast) was observed, but not both of them. The perceived two-color gratings show that two rivalrous chromaticities are both represented neurally when color and form are combined to give a unified percept. "Resolution" of competing chromatic signals from the two eyes is not restricted to color dominance and color mixture. The transition from misbinding to color mixture by increasing luminance contrast shows that luminance edges have an important role in correct localization of color.

Color Perception↗