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Andrew Coia, Michael Crognale; Cortical Responses to Real and Illusory Surface Colors. Journal of Vision 2015;15(12):253. doi: 10.1167/15.12.253.
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© ARVO (1962-2015); The Authors (2016-present)
In addition to the dominant wavelength of light reflecting off an object, our brain uses other visual cues to assign color to surfaces in the visual field. For example, boundaries of an area provide contextual clues to an object's color. Simply outlining the shape of an object on a piece of paper can produce a strong figure ground effect, delineating the enclosed area as the figure and outside area as the background. Furthermore, a strong illusory color can be seen when an area is outlined twice with two adjacent and differently colored lines. Under certain conditions, the enclosed region can adopt a hue similar to that of the inner line while the background often adopts a complimentary color. This illusion has come to be known as the watercolor effect by vision scientists. We have studied this illusion using the visual evoked potential and compared the electrical recordings to behavioral responses. By exchanging an image of the illusion with an image of a control stimulus at a rate of 4 Hz, a large 2 Hz response is elicited concurrent with the appearance of the induced color during every other image presentation. When two control conditions are exchanged, only a large 4Hz component is present. However when physical color is inserted into one of the controls, a measurable 2Hz component is produced. It remains to be determined which cortical areas in the color processing stream respond to the illusory color and in what order (e.g. feedback vs. feed forward). Consequently, we are currently using high density EEG to look at cortical activation, comparing activation elicited by illusory colors with activation elicited by real colors. In these studies, we are attempting to characterize the temporal and spatial distribution of the neurological basis for the sensation of induced color.
Meeting abstract presented at VSS 2015
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