Local Motion Signals PDF Download

This dissertation, "Local Motion in the Image Plane and in the Stereo-depth Plane Distorts an Object's Perceived Location and Spatial Arrangement" by Sum-yin, Tsui, 徐心言, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: ii Abstract of thesis entitled " Local motion in the image plane and in the stereo-depth plane distorts an object's perceived location and spatial arrangement" Submitted by Tsui Sum Yin for the degree of Doctor of Philosophy at The University of Hong Kong in February 2007 Vision is the sensory modality that provides the most useful means by which we identify the position and shape of distant objects. The results of many studies suggest that humans are able to gauge the relative positions of stationary stimuli very accurately. However, this process is highly dependent on a number of visual factors. For instance, image motion is known to affect spatial localization, such that when a motion signal is contained within a stationary object, the object's position appears to be shifted in the direction of motion. The present dissertation focuses on how the spatial arrangement and localization of objects is affected by two- and three- dimensional local motion. The perceived changes in position, size, and shape, of objects brought about by local motion give insight to the nature of the mechanisms underlying spatial and motion vision. It has been suggested that the centroid is one of the primitive spatial features of objects' positional alignment. As the local motion within an object initiates a perceived shift in its position, one possible reason for the shift is related to the perceived location of the centroid of the object. The results of the present studies show that the apparent size of a stationary stimulus that contains local motion is bigger than an identical stimulus that does not contain local motion. Specifically, theiii apparent increase of the size arises on the leading edge of the stimulus, and indicates a perceived shift in the perceived centroid of the stimulus in the direction of motion. It was further shown that the perceived shape of a stimulus for which the luminance distribution was physically skewed has its physical skew cancelled by local motion. Local motion within an object not only biases the perceived position in the two-dimensional image plane, but when local motion is indicated via stereo-depth, the perceived position of a stationary envelope which extends in stereo-depth is also shifted in the motion direction. This result suggests that local-motion-in-depth induces the misperception of position in depth in a similar way to image plane local motion, which induces a misperception of the position of an object. The illusory displacement of a single element brought about by local motion carries its effect over various spatial arrangements. When each element that contained local motion was lined up in a circular shape, the perceived size and shape of the object formed by the elements also varied according to the direction of local motion. Coherent local movement towards the center of the pattern leads to a perceived decrease in size of the pattern, and vice versa. Although the illusory effect was quite prominent, the magnitude of the effect is actually reduced when compared with that obtained from a single element. The findings of the studies suggest that local motion changes the spatial arrangement (size and shape) of a stationary element when it induces a perceived positional shift of the element. The mislocalization of objects that contain local motion also occurs in the stereo-depth plane in a similar manner, but the stren