Date on Master's Thesis/Doctoral Dissertation

8-2015

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Psychological and Brain Sciences

Degree Program

Experimental Psychology, PhD

Committee Chair

Essock, Edward

Committee Co-Chair (if applicable)

Shafto, Patrick

Committee Member

Shafto, Patrick

Committee Member

Hansen, Bruce

Committee Member

He, Zijian

Committee Member

Lyle, Keith

Subject

Space perception; Visual perception

Abstract

The relationship between the processing of orientations by the human visual system has been related to the orientation content of the natural environment; horizontal orientations, while predominant in natural environments, are perceived less well than vertical and oblique orientations are perceived best, though they are least prevalent in the natural world. This ‘horizontal effect’ has further extended the well-studied relationship between visual encoding and natural scene statistics as the differential perception of orientations in broadband scenes inversely matches their differential representation in the natural environment. However, the original hypothesis that this relationship may have evolved across millennia in order to make the visual system an efficient information-transmitting system has been called into question by research showing the modification of orientation perception by exposure to altered environments and studies showing a later development of adult-like orientation processing. Recent work into the effects of adaptation on visual encoding of the natural environment have led me to the conclusion that the relationship between the statistics of the natural world and visual encoding is, in a way, much simpler than previously posited; rather than being adapted over millennia to whiten the typical natural scene anisotropy, the visual system adjusts processing dynamically to match the current visual environment. The project presented here details how the statistics of the recently viewed environment affect the way that the visual brain processes information. To assess the effect of recent exposure on broadband orientation processing, the orientation content subjects viewed was modified via fast Fourier transform (FFT) filtering of their environment in near-real-time. Results show that experience in an altered environment modifies anisotropic processing: observers’ orientation perception changes from matching the typical environmental distribution to matching that of the recently experienced atypical environment. The results of these experiments can be predicted by assuming that observers’ biases of perception are probabilistic and rely on an internal model that matches the recently experienced environmental distribution. This change in perception indicates not only that orientation processing is plastic, but that it is related in a predictable way to an observer’s recent visual environment.

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