A look at colour

Judith Copithorne image

Judith Copithorne image

Back to the OpenMIND collection and a paper on colour vision (Visual Adaptation to a Remapped Spectrum – Grush, Jaswal, Knoepfler, Brovold) (here). The study has some shortcomings which the authors point out. “A number of factors distinguish the current study from an appropriately run and controlled psychological experiment. The small n and the fact that both subjects were also investigators in the study are perhaps the two most significant differences. These limitations were forced by a variety of factors, including the unusual degree of hardship faced by subjects, our relatively small budget, and the fact that this protocol had never been tried before. Because of these limitations, the experiments and results we report here are intended to be taken only as preliminary results—as something like a pilot study. Even so, the results, we believe, are quite interesting and suggestive.” To quote Chesterton, if it is worth doing it is worth doing poorly.

The researchers used LCD goggles driven by a video camera so that the scene the subject saw was shifted in colour. The shift was 120 degrees of a colour wheel (red to blue, green to red, yellow to purple). The result was blue tomatoes, lilac people, and green sky. (video) The study lasted a week with one subject wearing the gear all the time he was not in the dark while the other wore the gear for several hours each day and had normal vision the rest of the time. How did they adapt to the change in colour?

Colour consistency is an automatic correction the visual system makes so that colours do not change under different light conditions. Colours do not appear to change when viewed in sunlight, twilight, candle light, fluorescent lamps etc. What perception is aiming at is the characteristic of the surface that is reflecting the light and not the nature of the light. Ordinarily we are completely unaware of this correction. The colour shifting gear disrupted colour consistency until the visual system adapted to the new spectrum.

We did not test color constancy in any controlled way, but the subjective reports are quite nmistakable. Subject RG noticed that upon first wearing the rotation gear color constancy went “out the window.” To take one example, in normal conditions RG’s office during the day is brightly lit enough that turning on the fluorescent light makes no noticeable difference to the appearance of anything in the office. But when he turned the lights on after first donning the gear, everything had an immediate significant change of hue (though not brightness). He spent several minutes flipping the light on and off in amazement. Another example is that he also noticed that when holding a colored wooden block, the surfaces changed their apparent color quite noticeably as he moved it and rotated it, as if the surfaces were actively altering their color like a chameleon. This was also a source of prolonged amusement. However, after a few days the effect disappeared. Turning the office light on had little noticeable effect on the color of anything in his office, and the surfaces of objects resumed their usual boring constancy as illumination conditions or angles altered.” Interestingly the subject who wore the gear only part of each day never lost his normal colour consistency as he adapted to the other consistency; but the subject who wore the gear all the time had to re-adapt when he took off the gear although it took much less time than the adaption when the gear was first put on. I have often wonder how difficult it would be to lose this correction and for a while used a funny prism child’s toy to look at the uncorrected color of various shadows.

Did an adaption happen to bring the colours back to there original colours? Did the blue tomatoes start to look more red? It seems not, at least in this study. But again there were some interesting events.

On two occasions late into his six-day period of wearing the gear, JK went into a sudden panic because he thought that the rotation equipment was malfunctioning and no longer rotating his visual input. Both times, as he reports it, he suddenly had the impression that everything was looking normal. This caused panic because if there was a glitch causing the equipment to no longer rotate his visual input, then the experimental protocol would be compromised. …However, the equipment was not malfunctioning on either occasion, a fact of which JK quickly convinced himself both times by explicitly reflecting on the colors that objects, specifically his hands, appeared to have: “OK, my hand looks purplish, and purple is what it should like under rotation, so the equipment is still working correctly.”…the lack of a sense of novelty of strangeness made him briefly fear … He described it as a cessation of a “this is weird” signal.

Before and after the colour adaption period, they tested the memory-colour effect. This is done by adjusting the colour of an object until it appears a neutral grey. If the object always has a particular colour (bananas are yellow) then people over correct and move the colour past the neutral grey point. “One possible explanation of this effect is that when the image actually is grey scale, subjects’ top-down expectations about the usual color make it appear (in some way or another) to be slightly tinted in that hue. So when the image of the banana is actually completely grey scale subjects judge it to be slightly yellow. The actual color of the image must be slightly in the direction opposite yellow (periwinkle) in order to cancel this top- down effect and make the image appear grey. This is the memory-color effect.” This effect was slightly reduced after the experiment – as if bananas were not expected to be as yellow as they had been before the experiment.

They also looked at other aspects of adaption. “As we found, aesthetic judgments had started to adapt, … And though we did not find evidence of semantic adaptation, it would be quite surprising, given humans’ ability to learn new languages and dialects, if after a more extended period of time semantic adaptation did not occur.” They do not have clear evidence to say anything about qualia verses enactive adaptation but further similar experiments may give good evidence.

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