Our data are consistent with this hypothesis. The decline in sensitivity along the protan, deutan and tritan line we documented in the same set of observers Figure 5 suggests that these compensatory mechanisms are likely to arise at a late, probably cortical site and that these higher-order appearance mechanisms operate in parallel to the discrimination mechanisms revealed in the chromatic sensitivity task.
This dissociation between discrimination and appearance mechanisms is supported by Neitz and colleagues [31] , [32] who showed that shifts in unique yellow induced by long-term changes in the chromatic environment are not due to receptoral or sub-cortical changes, but must be of cortical origin, probably after chromatic information from both eyes has been integrated.
The question remains how these higher order colour mechanisms receive feedback on the strength of their cone inputs. Neitz et al's unique yellow data are consistent with the hypothesis that the gains of the L and M cones are adjusted such that the red-green opponent mechanism is at equilibrium for the average daylight [33] , but this recalibration is by no means complete [34]. Our results provide further evidence that the brain uses information about the statistical properties of our chromatic environment to adjust the weighting of the receptor signals to achieve hue constancy across the life span.
Our second aim was to assess whether there is a differential age-related effect of ambient illumination on hue constancy. Comparing the cone weightings under the dark viewing condition Figure 3 with those under adaptation to D65 Figure 6 and CWF Figure 7 reveals that the mean unique hue settings across the entire sample are not affected by the illumination conditions see also Figure S2a nd S3.
A closer look at the age dependency of the observed cone weightings Table 1 shows that there is a differential effect of adaptation on hue constancy: only under daylight D65 adaptation do the age-related changes in the green settings reach statistical significance Table 1 ; Figure 6 , row 2 ; what appears uniquely green for young observers appears more yellowish for older observers.
Older observers require more S cone input to achieve unique green when the settings are obtained under simulated daylight, but still much less than predicted by the lens model.
This is consistent with the idea that the yellow-blue mechanism YB G which is silenced by the unique green settings is most affected by the yellowing of the lens Eq. If the visual system were able to fully compensate for the changes in the optical media, the observed cone weightings should not vary with age.
We find that, under most of the tested conditions, this is the case; only under adaptation to daylight D65 , green hues change slightly with age.
In summary, we find evidence for compensatory mechanisms operating on higher-order colour functions and thereby ensuring that hue remains approximately constant despite the known age-related changes in the lens. The concurrent age-related decline in the chromatic discrimination sensitivity suggests that the neural site of these compensatory mechanisms is probably cortical; the underlying mechanism is still poorly understood, but is consistent with the idea that it is based on invariant sources in our visual environment.
Spectra, cone fundamentals and lens model. Each line indicates the transmission of a particular age group, from 20 to 80 y. From top to bottom. Hue settings for the lower and the upper age group under D Dotted lines indicate the observed unique hue lines summarised by the 1st principal component ; the solid lines denote the predicted unique hue lines assuming the lens model by Pokorny et al. Hue settings for the lower and the upper age group under CWF.
Details as in Figure 4. All predictions are made with respect to a year old observer. A subset of these data has been presented in the proceedings of the International Colour Vision Society, held in Norway, in I would like to thank Chenyang Fu for her help with data collection, Kaida Xiao for helpful discussion and Dimos Karatzas for his support in the design of the experiment.
Conceived and designed the experiments: SW. Performed the experiments: SW. Analyzed the data: SW. Wrote the paper: SW. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract It is well known that the peripheral visual system declines with age: the yellowing of the lens causes a selective reduction of short-wavelength light and sensitivity losses occur in the cone receptor mechanisms. Introduction The purpose of this study was to assess in a large sample of adult colour-normal observers whether higher-order colour appearance mechanisms are affected by ageing.
Stimuli and procedure To obtain settings of the unique hues we used a modified hue selection task [6]. Download: PPT. Chromatic specifications To calculate the cone absorptions in the long-, medium-, and short-wavelength-sensitive cones, we used the 2-deg cone fundamentals derived by Stockman and Sharpe [20].
Estimating the cone weightings Colour-opponent mechanisms were first mentioned by Hering [23] who proposed that any hue can be described in terms of its redness or greenness and its yellowness or blueness.
For example, when a subject adjusts the red and green component of a yellowish stimulus such that it contains neither red nor green, then the red-green opponent channel RG is at equilibrium; consequently a red-green opponent mechanism produces a zero response for this yellowish stimulus for details see [6] : 1 A yellowish stimulus with these differential L,M,S cone weights w L ,w M ,w S is void of any red and green, since it silences the putative red-green mechanism i. A bluish stimulus that contains neither red nor green, produces a zero response in a red-green opponent channel: 2 Unique red Eq 3 and unique green Eq.
The Lens model by Pokorny et al We used the lens model by Pokorny et al [16] to predict the changes in lens transmission as a function of age. Results 1. Effect of age on colour appearance To evaluate whether hue perception changes with age and whether these changes are predicted by the age-related changes in the optical media, we proceed as follows. Figure 4. Effect of ambient illumination on unique hue settings for different age groups Our second aim was to assess whether the adaptation mechanisms that underlie the hue constancy across age operate in a similar manner for different ambient viewing conditions.
Discussion Our main finding is that colour appearance mechanisms are to large extent unaffected by the known age-related changes in the optical media yellowing of the lens whereas the ability to discriminate between small colour differences is compromised with an increase in age.
Supporting Information. Figure S1. Figure S2. Figure S3. Acknowledgments A subset of these data has been presented in the proceedings of the International Colour Vision Society, held in Norway, in Author Contributions Conceived and designed the experiments: SW.
References 1. Journal of Physiology — View Article Google Scholar 3. Journal of Neurophysiology — View Article Google Scholar 4. View Article Google Scholar 5. Hurlbert A Colour vision: primary visual cortex shows its influence. Current Biology View Article Google Scholar 6.
Vision Research — View Article Google Scholar 7. Valberg A A method for the precise determination of achromatic colours including white. View Article Google Scholar 8. View Article Google Scholar 9. Cone-opponent axes. Journal of the Optical Society of America A — View Article Google Scholar Unique hues. Unique hues in Indian and United States observers. Mollon JD A neural basis for unique hues? Current Biology R—R Werner JS Visual problems of the retina during ageing: Compensation mechanisms and colour constancy across the life span.
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