Fig. 3: Change of Afterimage Hue with Chroma (Experiment 3).

a Visualisation of the effect of inducer chroma on afterimage hue. Numbers in the coloured rectangles indicate hue. Rows correspond to example inducer stimuli of constant hue (60 deg) and different chroma levels (20–70), the cone-opponent hue (240 deg), the prediction by cone-adaptation with varying hue, and the average hue of the prediction that is used for the analyses. The variation in chroma predicted by cone adaptation has been ignored here to facilitate the visual comparison of hue changes. b N = 216 inducer stimuli (coloured dots) varying across three levels of chroma (20, 50, maximum). The grey circles in the background indicate chroma (radius) varying from 10 to 80 in steps of 10. The doted tetragon shows the monitor gamut at that luminance level. c Afterimages modelled through cone contrasts. The black lines illustrate how afterimages vary when inducer chroma corresponds to the grey circles. Coloured dots indicate simulated afterimages for measurements with the N = 216 inducer stimuli of (b). d Comparison between measurements and cone-adaptation predictions. Grey dots are the N = 216 measurements; thick transparent black lines highlight the change across chroma for hues at 45-deg intervals. Grey lines indicate the reference average used to calculate hue-specific chroma differences. Red lines show the corresponding cone-adaptation predictions. e, f Scatterplots illustrating the correlation between simulated and measured changes of afterimage hue across chroma. The axes indicate the afterimage hue difference from the cone-opponent hue (e) and from the reference average (f) in azimuth degree. Dot colours indicate inducer colours. This figure shows results for observer f7. Results for four other observers can be found in Table 4 and Fig. S13, each replicating these results.