The Colors of Afterimages1. What are afterimages?

2. Afterimages as illusions or hallucinations

3. The colors of afterimages : A challenge to the objectivist approach to colors

4. The science of afterimages

5. What is the nature of colors?

6. A pluralist view of colors

7. A response to the challenge of afterimages

8. Conclusion

What are Afterimages ?

Some examples

1) Illusions are misleading or involve some kind of deception

Afterimages as illusions or hallucinations

2) Illusion and hallucination vs. veridical perception

The term “illusion” is to be understood here as applying to any perceptual situation in which a physical object is actually perceived, but in which that object perceptually appears other than it really is, for whatever reason. (Smith, 2002,23)

The man who reports a yellowish orange after-image does so in effect as follows: “ What is going on in me is like what is going on in me when my eyes are open, the light is normal etc. etc. and there really is a yellowish-orange patch on the wall. ” (Smart, 1963, 94 – 65)

Afterimages as illusions or hallucinations

“This problem would not arise if after-images were full-blown illusions. That is, if seeing an after-image consisted in seeming to see a material object suspended in physical space, then that object, though in fact illusory, could still appear to have the same colour quality as any other material object. But after-images are not seen as material objects, any more than, say, a ringing in one's ears is heard as a real noise. The items involved in these experiences are not perceived as existing independently of being perceived.” (Boghossian & Velleman, 1989, Colour as secondary quality, p. 87)

Afterimages as illusions or hallucinations

“Another case worthy of note is that which is often called “ having an afterimage. ” If one stares at a patch of color and then looks at a white surface, one has an inaccurate experience as of a patch of the same shape as the one stared at originally, but in the complementary color. Many philosophers would, I think rightly, count such cases as being cases of hallucination. If that is right then they are further instances of partial hallucinations, for one still sees the world when having an afterimage”F. Macpherson (2013). The Philosophy and Psychology of Hallucination: An Introduction. In F.Macpherson & D. Platchias (ed.), Hallucination: Philosophy and Psychology, MIT Press, p. 8

Afterimages as illusions or hallucinations

The Colors of Afterimages:

A challenge to the objectivist view of

colors

“We have it that certain mental objects, for instance, red after-images, belong to the extension of redness. These mental objects do not, though, belong to the extension of properties like having a certain surface grid or reflecting a certain distribution of wave-lengths. Therefore, redness is not any such scientific property, and likewise for colours in general.”Frank Jackson (1977), pp. 125-6.

Portfolio samples

The Science of Afterimages

Cone cellssensitivity

“If you sit for a while in a room full of long wavelength light, the long wavelength cone system will get fatigued relative to the other two systems, and will respond less than normal to further stimulation. If you now step outside and look around, the visual system will react as if there were a systematic decline in relative long wavelength lightness values. The effect is comparable to that of adding to daylight an additional middle- and short-wave illuminant. The scene will appear as if bathed in mixed blue and green, that is cyan auxiliary light. Colours will shift systematically. Reds will go dark. Yellows will go greenish. Magentas will go blue. Whites and greys will drift to cyan.” Keith Campbell

Additive Colors

The nature of colors

objectivist pluralistphysicalist

Reflectance

Color perception variations

1. interspecies color variations

2. intraspecies color variations / interpersonal color variations

3. intrapersonal color variations--> afterimages

The Color Uniqueness Principle

Philonous: To put it past all doubt, consider the following. If colours were real properties or qualities inhering in external bodies, they couldn’t be altered except by some alteration in the very bodies themselves: but isn’t it evident that the colours of an object can be changed or made to disappear entirely through the use of a microscope, or some change in the fluids in the eye, or a change in the viewing distance, without any sort of real alteration in the thing itself? Indeed, even when all the other factors remain unaltered some objects present different colours to the eye depending on the angle from which they are looked at. The same thing happens when we view an object in different brightnesses of light. And everyone knows that the same bodies appear differently coloured by candle-light from what they do in daylight. (...) Now tell me whether you still think that each body has its true, real colour inhering in it. If you think it has, I want to know what particular distance and orientation of the object, what special condition of the eye, what intensity or kind of light is needed for discovering that true colour and distinguishing it from the apparent ones.(Berkeley, 1734, Three Dialogues between Hylas and Philonous, first dialogue)

Surface spectral reflectances (SSR)

Metamers

Triples of Integrated (surface) Reflectance (TIR)

Portfolio samples

The Challenge of Afterimages

Filters : selecting the light

Perception in a long-wavelength light Perception through a “red” filter