Date of Award

May 2021

Document Type


Degree Name

Doctor of Philosophy (PhD)


Human Factors Psychology

Committee Member

Christopher C Pagano

Committee Member

Richard A Tyrrell

Committee Member

Patrick J Rosopa

Committee Member

Andrew Robb


Visually guided action in humans occurs in part through the use of control laws, which are dynamical equations in which optical information modulates an actor’s interaction with their environment. For example, humans locomote through the center of a corridor or through the center of two obstacles by equalizing the speed of optic flow across their left and right fields of view. This optic flow equalization control law relies on a crucial assumption: that the shape of the body relative to the eyes is laterally symmetrical. Humans engaging in tool use are often producing person-plus-object systems that are not laterally symmetrical, such as when they hold a tool, bag, or briefcase in one hand, or when they drive a vehicle. This dissertation tests a new generalized control law for centered steering that accounts for asymmetries produced by external tool use. Experiment 1 tested the efficacy of the generalized control law in a replication of Duchon & Warren (2002). Participants held an asymmetrical bar and centered themselves within a virtual moving hallway while the speed of the virtual walls were systematically changed. Experiment 2 assessed the application of the generalized control law to an aperture passability task, in which participants holding asymmetrical bars walked through real world apertures of various widths. The results of the current studies demonstrate that humans engaging with an asymmetrical tool can 1) perceive the asymmetry of a person-plus-object system, 2) use that information to modulate the use of optic flow equalization control laws for centered steering, and 3) functionally incorporate the asymmetrical tool into their perception-action system to successfully navigate their environment with a 97% success rate.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.