The Impacts of Visual Adaptation on Stimulus Salience
AdvisorWebster, Michael A.
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Adaptation is defined as becoming desensitized to a stimulus due to repeated exposure to that stimulus. All sensory systems rapidly adapt their sensitivity in response to changes in the stimuli they are exposed to. However, the exact function of adaptation remains unclear. This study examined the hypothesis that adaptation serves to highlight the perception of new information in the environment, by reducing sensitivity to the prevailing stimulus. This was tested by examining how adaptation changes the relative salience of information in hybrid images. A hybrid image is a mixture of two different images, one image that is low-pass filtered to remove fine details to appear blurry, and the other that is high-pass filtered to remove the blur and preserve only the fine details to appear sharpened. Which image is perceived by the observer depends on the viewing distance and on the relative contrast or strength of the two images. This study utilized a hybrid image composed of the faces of celebrities George Clooney and Brad Pitt to determine whether the image perceived also depends on the adapted state of the observer by testing whether the relative salience of the two images is altered by prior exposure to one of the component images. In addition, the study tested which aspect of the stimulus controls the adaptation: the identity of the image itself or the amount of blur in the image. The results of the study suggest that adaptation to the identity biased the perceived identity despite differences in the blur, while adaptation to the blur level biased the perceived level of blur regardless of identity. These results are consistent with the hypothesis that adaptation acts to increase the salience of more novel stimuli, and suggest that different attributes adapt independently.