Interaction between complex motion patterns in the perception of shape

Abstract

We investigated how different types of complex motion patterns interact in the perception of shape. We used global dot-motion stimuli which consisted of two superimposed groups of dots; one group of dots moved along an ellipsoidal trajectory (target pattern), while the other group of dots was divided into quadrants with dots in alternating sectors moving in radial expanding and radial contracting directions (background pattern). In the first experiment, observers judged whether the major axis of an ellipsoidal motion pattern oriented at 45 degrees or -45 degrees from vertical lay to the right or to the left of a central vertical line. Ellipsoids with different aspect ratios, which controlled both the tilt (left or right of vertical) and the extent of ellipsoidal curvature, were presented to observers using method of constant stimuli. The appearance of the ellipsoidal target pattern was distorted in the presence of background motion. The aspect ratio of the target at which observers perceived the figure to be circular was approximately 0.86 (an aspect ratio of 1.0 indicates a circle), with the pattern's major axis lying in the two sectors that contained contracting motion. This finding may constitute evidence that background motion distorts the perception of space, resulting in a distorted target pattern. However, the distortion effect is limited to conditions for which the speed of the target pattern and background pattern was slow and high contrast, and for when dots forming the target and background patterns were of the same luminance polarity.

The role of motion streaks in the perception of the kinetic Zollner illusion

“…In three experiments, the relative contribution of motion streaks to the perception of motion was examined by changing dot speed, dot contrast, and dot lifetime to generate shortened streaks. Previous investigations have shown that such manipulations impact on the availability of motion streaks in the computation of motion direction (Apthorp & Alais, 2009;Apthorp et al 2010;Edwards & Crane, 2007;Li et al, 2008). Experiment 1 examined the effect of dot speed on the extent of tilt induction.…”

“…If motion-tilt induction does indeed arise from lateral inhibition (or an analogous operation) between the background orientation and the motion streak produced by object motion, it would be predicted that reduction in the availability of motion streaks would result in a veridical percept of the object's trajectory. Previous studies have well established that reducing object speed, stimulus contrast, and motion length are effective means of attenuating the salience of motion streaks (see Edwards & Crane, 2007;Li, Khuu, & Hayes, 2008). The present study adopted these stimulus manipulations and investigated whether attenuating the salience of motion streaks by reducing image speed (Experiment 1), object contrast (Experiment 2), and streak length (Experiment 3) impacts the perception of the kinetic Zollner illusion, which typifies motion-tiltinduction effects observed in kinetic geometric illusions.…”

Motion Streaks Do Not Influence the Perceived Position of Stationary Flashed Objects

“…However, the distortion was observed only at slow background speed, and when dots had high contrast and were of the same luminance polarity. It should be noted that in the case of Li et al [28] the motion defined shape of the object was always clearly discernable, and the speed at which moving dots affected the shape of the ellipsoid was below the critical speed for motion streaks. Indeed, dots diameter was ~6 arcmin and, based on Geisler [1], for ~6 arcmin dots, streaks start to emerge at a speed of ~2.5 deg/s.…”

“…Thus, the contracting dots induced a distortion of the illusory edges of the Kanizsa triangle along the motion direction. However, Li et al [28] showed that using a motion-defined contour, the presence of fast moving dots (speed > 2.5 deg/s) in the background did not affect the perceived shape of the motion-defined contour. In particular, the authors investigated how complex motion patterns affected the perception of shape.…”

“…Motion streaks, arising from fast moving feature, are able to influence only the shape of illusory contours [9], where the spatial uncertainty is very high. However, motion streaks do not influence the perceived spatial position of discernable objects (e.g., Gaussian blobs or motion defined contours [28]) by inducing local distortion of the shape. In addition, our data support the notion that motion blur and motion deblurring/sharpening mechanisms constantly interact.…”