Keetaek Kham | PubMed Health

PubMed2005

Bistable Glass-pattern motion reveals two different processes.

Examining the two motion processes is an elusive task due to the difficulty of finding a proper stimulus paradigm. A rotational Glass pattern created with a random-dot array by superimposing its rotated version on the top of it can provide such a paradigm. If we displace only its rotated part in the vertical or horizontal direction, a bistable motion occurs; local dot motion in the same direction and Glass-pattern motion in the orthogonal direction. From two experiments, we found local dot motion is predominant in short spatiotemporal range and global pattern motion in long spatiotemporal range. Since the stimulus allows us to maintain all of its properties identical except for the changes in spatiotemporal parameters, this result shows more robustly that the energy-based first-order motion favors short spatiotemporal ranges while the pattern-based second-order motion favors long spatiotemporal ranges.

Humans↗

PubMed2004

An opaque surface influences the depth from the Pulfrich phenomenon.

When a pendulum, swinging in a frontoparallel plane, is viewed with a neutral density filter before one eye, the pendulum bob appears to rotate in an elliptical path. This illusion, known as the Pulfrich phenomenon, was used to examine depth cue interaction in a natural environment. An opaque surface was placed behind the pendulum. This intervention put the 'Pulfrich depth' of the pendulum in conflict with the information provided by other depth cues, such as interposition, and observers reported that the 'far' part of the pendulum's Pulfrich trajectory appeared to be flat. This was not the case when the surface was transparent. If the opaque surface was placed farther behind the pendulum's physical path, the far trajectory became increasingly elliptical. These results suggest that the opaque surface influences the pendulum's depth qualitatively and quantitatively. That is, the depth order between the surface and the pendulum is determined by interposition, but the absolute depth of the pendulum's Pulfrich trajectory is constrained by the surface's depth.

Adult↗