Date of Award

Spring 2012

Project Type

Dissertation

Program or Major

Psychology

Degree Name

Doctor of Philosophy

First Advisor

Andrew B Leber

Abstract

Visual illusions, such as motion-induced blindness, arise when the visual system, balancing speed and efficiency, summarizes the information it receives to form a percept. Motion-induced blindness (MIB) is characterized as the disappearance of a salient target when surrounded by a moving mask. Efforts to determine the mechanism have focused on the role of target characteristics on perceived disappearance by a coherently moving mask. In this dissertation, I take another approach, paying specific attention to the role of motion characteristics of the mask.

In Experiments 1, 2, 3, and 4, I investigate whether the property of common fate influences target disappearance by manipulating coherence of the mask elements. Results showed that as mask coherence increased, perceived target disappearance decreased. This pattern was unaffected by the lifetime of the moving dots, the dot density of the motion stimulus, the target eccentricity, or the number of motion trajectories contained in the mask.

The finding that motion coherence preferentially affected MIB prompted Experiments 5, 6, 7, and 8. Specifically, these experiments sought to investigate the spatial influence of mask motion on target disappearance. MIB was measured during conditions where opposing areas of motion coherence were confined locally surrounding the target or in more global areas across the display. The results revealed that motion coherence at more global locations, particularly at the area of fixation, had more influence on target disappearance compared to the coherence in proximity of the target and may reflect inability of the visual system to form a global motion pattern.

The possibility that global motion may give rise to MIB, motivated the final research avenue. Experiment 9 addressed the possibility that variability in motion processing of the mask affects target disappearance. Specifically, the strength of motion processing was measured using the motion aftereffect. Results showed a strong connection between the amount of motion processing dedicated to the mask and the amount of MIB.

As a whole, the findings show that motion processing, particularly during MIB, may be a driving force in our ability to perceive other objects in our environment.

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