A Paradoxical Misperception of Relative Motion
By Eric Craypo
Significance
We describe a paradoxical situation whereby a small object moving within a high-contrast, world-fixed background does not appear to move relative to it. This only occurs when that small object is moving in a direction that is consistent with retinal slip; otherwise, the motion is readily detectable with hyperacute precision. We show that motion of the background image across the retina is the primary source of informing the visual system of its direction and magnitude of eye motion and that this information is used not only to stabilize the percept of a background image ever-moving on the retina, but to selectively stabilize the percepts of any additional stimulus motions with a consistent direction, but not magnitude.
Abstract
Detecting the motion of an object relative to a world-fixed frame of reference is an exquisite human capability [G. E. Legge, F. Campbell, Vis. Res. 21, 205–213 (1981)]. However, there is a special condition where humans are unable to accurately detect relative motion: Images moving in a direction consistent with retinal slip where the motion is unnaturally amplified can, under some conditions, appear stable [D. W. Arathorn, S. B. Stevenson, Q. Yang, P. Tiruveedhula, A. Roorda, J. Vis. 13, 22 (2013)]. We asked: Is world-fixed retinal image background content necessary for the visual system to compute the direction of eye motion, and consequently generate stable percepts of images moving with amplified slip? Or, are nonvisual cues sufficient? Subjects adjusted the parameters of a stimulus moving in a random trajectory to match the perceived motion of images moving contingent to the retina. Experiments were done with and without retinal image background content. The perceived motion of stimuli moving with amplified retinal slip was suppressed in the presence of a visible background; however, higher magnitudes of motion were perceived under conditions when there was none. Our results demonstrate that the presence of retinal image background content is essential for the visual system to compute its direction of motion. The visual content that might be thought to provide a strong frame of reference to detect amplified retinal slips, instead paradoxically drives the misperception of relative motion. Read More.
Video
This video illustrates a paradoxical illusion: normally the human visual system is exquisitely sensitive to detecting relative motion, but in this special condition that we programmed, this sensitivity is suppressed. Slide 1 shows an object (red dot) moving within a frame of reference and the magnitude of motion is easily detectable. Slide 2 shows the same red dot but we programmed it to move in the exact opposite direction to retinal motion. The video beside it represents the magnitude of motion that the subject saw when viewing this stimulus.