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David Lewis, Sieu Khuu; Quantifying the perception of colour in visual saltation. Journal of Vision 2010;10(7):435. doi: https://doi.org/10.1167/10.7.435.
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© ARVO (1962-2015); The Authors (2016-present)
In the visual saltation illusion, stimuli are presented first to one location then another in rapid succession which produces the illusion of the intermediate stimuli as jumping in equidistant steps between the two locations (Geldard, 1975). Geldard also noted that if stimuli at the two sites of stimulation were of different colours, the apparent colour of the mislocalised stimuli appeared to be a mixture of the two colours. For example, if stimuli at one site was red and the other site was green then the mislocalised stimuli would appear yellow. In the present study, we systematically quantified this illusory colour change with different colour combinations. In Experiment 1, observers were presented with 3 coloured bars (0.5x2deg, inter-stimulus-interval of 0.25 seconds); two bars of the same colour were flashed at one location (10 degrees to the right of fixation), and one bar of a different colour was flashed at another location (15 degrees). Saltation was noted with the second bar appearing mislocalised between the first and third bars, and six observers were required to adjust the colour and position of a probe to match the perceived colour and position of the mislocalised bar. We observed that the perceived colour of the mislocalised element does not correspond to its physical colour for a range of colour combinations, but appears to be of an equal mixture of the two physical colours. Additionally, in Experiment 2 we showed that the perceived colour of the mislocalised element can be altered by briefly changing the colour of the background coinciding with its perceived position, and the resultant colour is equal to a mixture of the perceived colour of the bar and the background colour. This finding indicates that phemeonological colour perception in visual saltation relies on the perceived colour and not the physical colour of stimuli.
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