Current Research Interests

My primary focus has long been on the mechanisms and processes that establish and maintain the homeomorphic and veridical mapping of the spatial senses necessary for perceptual-motor coordination. This investigation is guided by a model which views the adaptive perceptual-motor system as composed of a number of autonomous but cooperating sensory-motor systems (e.g., eye-head, ear-neck, and hand-arm). Each such subsystem includes encoding functions that map sensory and motor afference onto a common noetic space and is, therefore, capable of operating independently of any other subsystem. However, sensory-motor systems can be coordinated by the exchange of guidance signals via directional linkages such that one (guided) system responds to noetic coordinates originating in another (guiding) system. Naturally occurring misalignments of systems (e.g., arising from growth, pathology, or drift) produce local discordances in and realignment of encoding functions in the guided system(s), thereby reestablishing a one-to-one noetic mapping with the guiding system, and the frequent reversals in direction of guidance between systems required by everyday task performance assures that alignment in all parts of the total system converges on a (veridical) noetic space which represents physical constraints. I have also applied my interest in cognitive theories of attention to the central regulation of the directional linkages between systems, and a knowledge of motor control theory has proven essential to modeling in detail the intra-system adaptive mechanisms.

My primary approach to the questions raised by this model incorporates a long-standing view of prism adaptation as an experimental example of the natural adaptive capacity of the perceptual-motor system to maintain alignment among its various subsystems in the face of naturally occurring discordances. This research has revealed a distinction between extraordinary realignment of spatial maps and ordinary strategic spatial remapping between coordinated sensory-motor systems to achieve optimal adaptive performance. Prism exposure evokes both extraordinary realignment and ordinary recalibation. My research has developed methods for distinguishing between these two adaptive processes and for assessing their relative contribution to prism adaptation.

Currently, I am applying theory and data from normal prism adaptation toward understanding the ameliorating effects of prism adaptation for left unilateral neglect patients. Neglect is, in part, identified with dysfunction in higher-level calibration of the task-work space that is ameliorated by lower-level realignment of origins for sensory-motor coordinate systems. Transient prism-induced realignment substitutes for dysfunctional calibration in affected systems, producing "recalibration" that persist and provides additional opportunities for learning after normal alignment has been restored. Amelioration generalizes to tasks with similar spatial attributes and tasks that implicate the sensory-motor systems exercised in prism exposure. Investigation of therapeutic prism adaptation requires methodology that permits identification of the loci of both the calibration dysfunction and ameliorating realignment.

I also pursuing my interest in illusion research. In particular, I am exploring the possibility of identifying the 3-D virtual structure that may underly the 2-D Müller-Lyer illusion. Major theories of the illusion assume that the linear perspective present in these drawings erroneously evokes natural perspective processing and that such inappropriate processing produces the illusion: the visual system responds with what should be there given the perspective present. My boot-strap research strategy is to try out various virtual structures and transformations of those structures to empirically determine how well they account for the illusion. To date, convex and concave virtual corners in front of and behind the picture plane, respectively, have produced reasonably good matches for arrow and fork illusions, respectively, under transformations of station point and corner rotation. Ultimately, I hope this work will bear on the question of whether a solution to the inverse perspective problem is required or a cue based approach can be successful.