Abstract
Surface coloration can be achieved by physically coloring in a surface or alternatively by induction from edges. One visual illusion known as the watercolor effect demonstrates how color from edges can spread within a boundary. The coloration of the watercolor effect resembles a desaturated hue of the inducing line, or a mixture of the inducing line with the uncolored surface. It is debated whether this spreading of color is due to an active process of filling in the retinotopic maps in the cortex or through a more symbolic neural representation assigning color to a region of space. Both early visual as well as ventral occipital cortical areas are thought to contribute to the percept of color vision. The current study looks at neural processing associated with physical color vs. edge-induced colors using high density (HD) EEG source estimation. This method estimates the intensity and time course of activity on the surface of the cortex from which the electrode signals on the scalp are generated. We previously used steady state VEP to measure the watercolor illusion. We performed a similar HDEEG experiment with single black lines and in addition added a second colored line, which in an aligned state produced the watercolor illusion, and in a misaligned state produced a control stimulus with contours but no induction. Pattern reversals of two misaligned control stimuli were recorded as comparison. We inserted physical filled-in color to one of the two reversing controls and generated a fundamental color frequency independent of alignment. These SSVEPs were complemented with pattern onset VEPs which showed the stimulus followed by a blank screen. The onset VEPs show the propagation of the neural signal from early visual areas (V1/V2) to more ventral occipital areas. Further analysis on the SSVEP reveals phase propagation of contour alignment, illusion, and physical color.
Meeting abstract presented at VSS 2016