Browsing by Subject "Visual adaptation"

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    TSTM: A two-stage tone mapper combining visual adaptation and local contrast enhancement
    (University of Minnesota. Institute for Mathematics and Its Applications, 2009-05) Ferradans, Sira; Provenzi, Edoardo; Bertalmio, Marcelo; Caselles, Vicent
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    Visual mode switching: Behavior & Neuroimaging
    (2023-04) Li, Yanjun
    "Color context effects" describe empirical results or phenomena where a surround, either in space or time, changes perception of the color of a target. The strength of color context effects may be influenced by our familiarity with the specific context. We term stronger and faster context-dependent processing under familiar contexts “visual mode switching”. Mode switching could help to stabilize vision in the changing visual environment and aid many perceptual goals, including improving the detection or discrimination of objects and their properties, and making neural codes more efficient. This dissertation presents three behavioral studies investigating whether visual mode switching can be learned through experience with a context, and whether it affects many stimuli in a given environment. Study 1 explored whether mode switching can occur after wearing strongly tinted glasses for five 1-hr periods per day for five days. We found that over days the tint faded more and more rapidly upon donning the glasses, indicating that the visual system learned to rapidly adjust to the tinted environment, switching modes to stabilize color vision. Study 2 tested whether wearing tinted glasses for a single 5-hr period each day for five days suffices for learning to switch visual modes. We found that mode switching can be acquired from a once-daily experience. In study 1 and 2, we tested for changes in the perception of unique yellow, which contains neither red nor green. Study 3 explored whether effects of mode switching can apply to many stimuli affected by the environmental change. We used a dissimilarity rating task to measure and track perception of many different colors, and found that colors across the color space appeared more and more normal immediately after putting on the glasses. These findings may help to predict when and how mode switching occurs outside the laboratory. Lastly, in study 4 we conducted a pilot functional MRI (fMRI) experiment to investigate the neural mechanisms of visual mode switching. We adopted a similar paradigm as in the behavioral studies. The fMRI design worked well and allowed us to identify brain regions that had changes in their responses to colors seen while wearing the red glasses before and after five days of experience with them. We found that both the primary and extrastriate visual cortex may be involved in mode switching. Taken together, these findings help us better understand how experience alters both visual perception and cortical processing of color.