Date of Degree
PhD (Doctor of Philosophy)
During everyday scene viewing, the information received by the visual system is frequently disrupted: Objects are often occluded by other objects, and sensory processing is interrupted by eye, head, or body movements. The visual system is extremely efficient at correcting for these interruptions and in establishing object correspondence and perceptual continuity. At the end of this correspondence process, the visual system is left with two representations of an object: The initial representation and the one acquired after the disruption. In the present dissertation, I investigated the mechanisms by which the visual system reconciles these discontinuous inputs to give us a perception of a smooth and stable visual world.
To achieve this, I ran four experiments in which participants were presented with a colored saccade target, and instructed to remember its color before executing the saccade. On some trials, the color of the saccade target was changed to a new value during the saccade. Participants were asked to report either the pre- or post-saccadic color value in a continuous report task. Object continuity was manipulated in two ways. The target blanking paradigm served as the main manipulation of stability: On half the trials, the target was removed from the screen during the saccade, disrupting object continuity. In addition, the magnitude of color change was used as a secondary manipulation of visual stability. The color report data were fit with probabilistic mixture models. First, there was no evidence for integration of pre- and post-saccadic feature values into a composite representation. Instead, on a majority of trials participants could successfully retain and report both pre- and post-saccadic states of the target object. Further, these two states dynamically interacted with each other, resulting in their feature values systematically shifting toward each other. Lastly, when reporting the pre-saccadic color, participants were more likely to incorrectly report the post-saccadic color under conditions of visual stability versus instability, supporting a probabilistic overwriting mechanism. Together, these results are more consistent with an object-based model, rather than an image-based model of representational updating. Although the present study only focused on transsaccadic updating mechanisms, similar mechanisms are likely to be functional in many common situations where the visual system needs to establish perceptual continuity across disruptions and changes.
People frequently move their eyes to gather information about the objects in the world. The most common types of eye movement are saccades, rapid eye rotations to extract detailed visual information. During each saccade, the visual input is disrupted; thus, creating a problem for our visual system. In the current project, I investigated how the visual system integrates information we perceive before and after a saccade to enable the perception of a continuous visual environment. To determine the underlying mechanisms of this updating process, participants were presented with a saccade target, and instructed to execute a saccade to it. The continuity of the target was manipulated by both removing it from the screen and by the changing its color during the saccade. At the end of each trial, participants reported either the first (pre-saccadic) or the second (post-saccadic) color. The results revealed two main mechanisms of representational updating. First, color value of the pre-saccadic representation was more likely to be replaced by the post-saccadic color value when the target was perceived as continuous, compared to when its continuity was disrupted. This overwriting was not an automatic process; however, because participants could successfully report both pre- and post-saccadic colors on a majority of trials. Second, pre- and post-saccadic color reports were shifted toward the other color value, indicating a dynamic interaction between them. These results provide evidence for two main mechanisms by which the visual system updates object representations when faced with perceptual discontinuity.
publicabstract, Object-mediated updating, Transsaccadic updating, Visual stability
xiii, 155 pages
Includes bibliographical references (pages 144-155).
Copyright 2015 Ayse Caglar Tas