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Daniel R. VanHorn, Gregory Francis; Switch color afterimages suggest cortical mechanisms. Journal of Vision 2007;7(9):278. doi: 10.1167/7.9.278.
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© ARVO (1962-2015); The Authors (2016-present)
We used a two-stimulus afterimage to explore color afterimages. An oriented bar grating followed by a bar grating of the opposite orientation leads to an afterimage that is perceived as the same orientation of the first grating. Previous work on the reported color of these afterimages (Francis & Schoonveld, VSS 2004) found that most of the time the reported afterimage was the color complement of the bars of the first bar grating. This suggested that the mechanisms involved in negative color afterimages were contributing to the percept of the two-stimulus afterimages. We now report new experimental results that demonstrate the involvement of additional mechanisms. We varied the colors of the first bar grating, whose alternating bars were not color complements, and asked observers to report the afterimage color behind a fixation mark. Reports consistent with a negative color afterimage were sometimes reported, however the most common report was that the afterimage color had switched from the bars of the first grating. Thus, a blue/white bar grating led to an afterimage that was colored white/blue, with the color switching between bars. We hypothesize that opponent mechanisms at retinal (negative afterimage) and cortical (switch afterimage) levels both contribute to the afterimage percept with some situations favoring one over the other.
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