SENSORY EXPLORATION
Sensory Knowledge
Part I: Sensory Exploration
Chapter 1. Introduction to Part I: Colour Exploration
Pick something up in your right hand.What colour is it? How would you find out?
Your first move is to look at it. Suppose it looks red. This helps you answer the question. Based on what you have seen, you think it’s red. (You mean this as a colour category judgement, let us imagine, not one about shades of colour.) But now a cheeky interlocutor challenges you. “Are you sure?” she asks. “Would you care to bet on it?” Suddenly, it has become more important that you get it right.
What do you do now?
I. Determining Object Colour
Most of us who are normally sighted know how to exercise care in the verification of object-colour. First,we take the object into good, bright light – preferably indirect midday sunlight, bright enough to maximize detail, but not so bright as to dazzle or confuse. Note: “good” light is not necessarily white or orthochromatic light – light in which all visible wavelengths are equally intense. Polychromatic light – light in which many different wavelengths are well represented – is often good enough. Most of the time, we are in polychromatic, but not orthochromatic, light: artificial light from incandescent bulbs is yellowish, from fluorescent bulbs bluish;direct sunlight is biased toward yellow, light from the sky toward blue; orlight under the green leaves of a tree is greenish. These conditions are good enough for you to determine whether an object is red or not. It is also good enough for discriminating crimson from scarlet – i.e., recognizing them as different when both are presented side by side. But the more the illumination dominates in one colour at the expense of others, the more hard-pressed you will be to identify exact shades – to tell, for example, whether something is crimson or scarlet.
So the first rule for determining whether something is really red is to make sure that you are examining it in polychromatic light, and, if you are not, to take it into polychromatic light. How can you tell that the light is not good, and that you should seek better light? Normally, you can tell whether the light is polychromatic by looking to see whether the scene is polychromatic. In close-to-monochromatic illumination – in sodium or other garish fluorescent lighting, for example – distinct colours get assimilated to one another, and the colour palette becomes restricted. If you can discriminate a lot of colours, then, the lighting is good. (The converse does not hold, of course – in a scene that contains only objects of one colour, even panchromatic light will reveal only one colour.)
Along similar lines, we know how to tell whether the lighting is bright enough. In dim light, our pupils dilate, rod vision comes into play and colours merge to black and white, and there are fewer bright objects; in dazzling light, our pupils contract, our temples hurt, colour gets washed out, and there are no inky blacks to be seen. When we observe such effects, we know that the lighting is not good for colour discrimination – it is too dim, or too bright. A cautious, careful, and conscientious perceiver would check that the lighting was good before certifying a perceptual judgment about colour. Sometimes, of course, good light is not available. If not, it may be that you are temporarily unable to achieve the level of surety you desire.
There are other ways to test your colour determinations. Justin Broackes (2010) opens up a new way of thinking about this. He is discussing colour-determination among colour-deficient perceivers,[1] and notes that such perceivers compensate for their insensitivity to certain colour differences in one set of circumstances by usingclues gathered over a period of time in different sets of circumstances. “A red and a green thing that look [to a dichromatic observer] indistinguishable in one kind of illumination may behave differently as the illumination changes,” he says.
Suppose the light changes from the yellow of direct sunlight (D55) to the blue of the remainder of the sky (D75)—perhaps a cloud covers the sun, or a person picks up an object and turns it so it catches the light from a different part of the sky. Then it may happen that a red and a green thing that were indistinguishable [to the colour-deficient viewer] earlier will come to look different: the red thing will have darkened in relation to other things, while the green will not. (Green is more or less equally “close” to a blue illuminant and to a yellow; red is always “farther” from a blue thanfrom a yellow.) If a pair of red and green things initially looked equal in lightness, then the red will now look darker. (ibid, 340)
These variations of illumination can be observed in many different ways: by turning an object over in one’s hands, by observing the effect of different kinds of illumination available in a scene, and so on.
Broackes is colour-deficienthimself. (He is an anomalous trichromat, which means that the sensitivity range of his long-wave cone receptor is shifted towards the middle of the spectrum. He is not, therefore, a protanomicdichromat, who is missing a long-wave receptor altogether, but his ability to discriminate is reduced in a way that approximates a protanope.) He reports that when he manipulates objects in the ways described above – turning it, taking it into subtly different illuminations, etc. – he actually sees colours that were not visible earlier. (Traditionally, it has been claimed that dichromatsand anomalous trichromatssee less than the full range of colours. Broackes challenges this,citing many reports of dichromats.) Things that originally looked one colour begin to look different once he has had a chance to examine them closely.
I confuse certain reds and greens and am protanomalous. Unsurprisingly (being an anomalous trichromat), I have on occasion quite definite sensations of red (e.g., from fire engines) and of green (e.g., from grass). More surprisingly, however, there are things that look definitely red to me at one time and definitely green at another. And there is a particularly remarkable way in which this can occur. I may see an object and take it to be red (this has happened to me with the dark painted walls of a dining room, with a Lederjacke seen in the window of a shop in Salzburg, and with a multitude of things large and small). A moment later, I may realize I cannot be sure after all – with reds (or greens) like this, I know I sometimes make mistakes. I may then lift up the object and move it around, or (if I can’t move it) move my head to see it from different angles in different lighting; I may take it over to the window (or look at another portion of that same wall, closer to the window); and then suddenly, perhaps, I realize that it looked red; now it looks green; and these are two quite different ways a thing may look. At that point, if not just before, the object comes to lookgreen. . . Taking the object back to the place where it had first looked to me red, I still see it as green, just as I now take it to be. (ibid, 361)
This shows, as Broackes rightly argues, that what sensory exploration achieves is not merely inference, but an actual change in colour phenomenology, i.e., in how things look. It is not just that after manipulating something apparently red, the colour-deficient perceiver may come to realize that it is actually green. Rather, close examination and manipulation bring it about that it actually looksgreen. It is not entirely clear how this happens. It may be that his new belief changes, or cognitively penetrates, the phenomenology. (But he suggests that the object may come to look green “just before” he realizes that it is.) Or possibly it looks green when he looks at it a certain way, and once he realizes it is green, this is the more natural way of looking at it – Broackes says that he can subsequently make the colour shift in the manner of an aspect shift. However this may be, the important point is that by manipulating an object and viewing it in a variety of conditions, Broackes is able not only to determine its true colour, but to see it that way.
The methods of colour-determination used by colour-deficient perceivers are also available to the normally sighted. It is true for the normally-sighted too that information that is not available at a moment is available given manipulation and examination in sufficiently varied conditions. Colour-deficient perceivers learn these techniques “over many years”, Broackes says (ibid 335); skilled colour-sensitive perceivers may also learn how to use these cues – sometimes not even knowing that this is what they are doing. This, then, is a second way we may verify object colour: we may examine things in a variety of good (but possibly sub-optimal) lighting conditions and examine how its appearance changes. When directly lit by a fire, a pink thing looks a bit yellower than it would in direct sunlight; however, when rotated away from direct red-yellow illumination so that it catches more of the fluorescent light coming from your energy-saving reading lamp, it will darken less than a genuinely red-orange surface, since the latter is deprived of the light of which it reflects more. So if an object darkens more than you expect it when rotated, you may suspect that it is not the colour it looks to be. Moving objects around – from one kind of illumination to another, from direct lighting to shadow – and turning them over in your hands helps reveal their true colour.
Here is a cautious moral that one can take from Broackes’s tale. Suppose that the thing you are examining looks distinctly red. No matter how confident you are that it is really so, it is good practice to turn it about and examine it in a variety of lighting conditions to determine whether it darkens, lightens, sparkles etc. in ways that cast doubt on your initial determination. Conscientious perceivers – decorators, painters, designers, etc. – undertake this sort of exploratory procedure, and find better light if necessary, before they attach full credence to a perceptual judgement regarding the colour of an object. When they have done so, they are justifiably more confident of their judgements.
Another point to be noted here is that illumination and reflectance are not inextricably mixed up together in the way that many philosophers assume. When we try to find out what colour light is, we are not limited to looking at the objects on which the light falls. Illumination is often directly observable because it is reflected off shiny surfaces, including metallic objects, liquid surfaces, and people’s noses, foreheads, and bald pates. (Such reflection is entitled “specular”: see Lee 1992 and Macleod 2003 for its effects on colour perception.) A surface reflecting reddish light to the eye may be seen as white in recognition of the reddish light being reflected off a metallic surface close by. So to gauge the colour of something requires one to look at the entire scene in which it is set. This requires agency: the subject must scan the scene and focus on various parts of it. Again, where the light has thus been found to be red, a surface reflecting reddish light might actually look white in many such cases – its colour is not merely inferred but seen.
A second thing to be checked is surround colour.
The above image (which is reproduced by kind permission of Beau Lotto[2]) represents a three-dimensional box with its front face in the shade. The illumination appears to be from behind. The light and dark stripes appear to be of the same colour, though of course, they are less well lit on the front face. If we were looking at the actual box, we could easily verify this. We could move around and view the box from different distances and angles; we could turn the front face into the light or shine a light on it.
Put aside the question of the three-dimensional box that the image represents. Look more closely at the two-dimensional image itself. Question: are the lower parts of the light stripes (i.e., the parts that represent the front face) darker or lighter than the upper parts of the dark stripes? They look a lot lighter, and taking them into good light will only confirm this. But they are not! In fact, they are exactly the same colour. You can verify this by viewing these objects in isolation. So to determine how bright or dark these parts of the image are, you must view them in isolation. Again, this is something that skilled and conscientious colour-perceivers do: often, for instance, they use their hands to frame something and look at it in isolation.
Finally, you must make sure that you are in a good condition yourself. After you have been exposed to a bright red light, or have stared at a red surface for a while, everything looks a bit greener. Usually, such effects are transient – you can see things returning to normal. Resting your eyes, running your eyes over things so that they affect more than one part of your retina – these are good practices for colour-determination.