Motion Silences the Perception of Changing Image Quality in Naturalistic Videos
26.424, Saturday, May 11, 2:45 - 6:45 pm, Orchid Ballroom
Lark Kwon Choi1,3, Alan Conrad Bovik1,3, Lawrence Kevin Cormack2,3; 1Department of Electrical and Computer Engineering, The University of Texas at Austin, 2Department of Psychology, The University of Texas at Austin, 3Center for Perceptual Systems, The University of Texas at Austin
Failure to detect changes in stimulus luminance (or color, etc.) termed "silencing" occurs in the presence of rapid motion (Suchow and Alvarez, 2011). It is possible that silencing is useful in naturalistic contexts, serving to suppress the perception of cast shadows on moving objects, say, or preventing video artifacts from being distracting. We conducted human experiments examining the perception of "flicker" caused by variation in image quality for moving objects in videos. 42 naive subjects evaluated the amount of perceived flicker of moving objects in the random ordered 36 test videos, which included six flicker-free reference videos and 30 degraded, flickering videos. The flicker was generated by alternating video frames of different quality levels (e.g.: bad, poor, good, and excellent). An eye and head tracker (faceLAB 5, Seeing Machines) was used to monitor gaze position (subjects heads were unrestrained), and subjects reported their percepts by moving a mouse continuously throughout the stimulus presentation. The results indicate that the reduction of the visibility of flickering in natural videos depends on both the overall video quality and the speed of motion. When the video quality was high, the perceptual visibility of flickering is low and less sensitive to motion, whereas when the video quality was poor, the impact is large. Furthermore, although subjects held their gaze on the moving objects, less flicker was seen on fast-moving objects. We interpret this result to suggest that large coherent motions near the fixation point might silence the awareness of flickering on natural videos. The responsible mechanism might be useful in the real world, where the light coming from moving objects can change dramatically (due to passing through areas of light and shadow, e.g.) even for a rigid object with a constant trajectory.