CNS 186/Color Psychophysics            CNS186-color-02/18/08
 
Color Psychophysics    
(Shinsuke Shimojo)
 
1. Do colors exist?
- Layman's view: "Of course, they are properties of objects' surfaces."
- Physicists' view: "They are nothing more than wavelengths of reflected
    light from objects' surfaces."
- These are not totally wrong, but insufficient, because without referring to
    receptors and neural mechanisms, we can not define colors, as will be
    discussed below.
- Munsell Book of Colors (=psychological space of colors).
    Color is actually a psy chological entity.
- Newton's color spectrum, additive and subtractive colors, etc.
    These may seem to indicate that all color issues are optical problems,
    but they are not. Eg. color mixture (metamer).
 
2. How are colors created?
- Anatomical structure of retina, and photo receptors.
- Rhodopsin and transmission of light energy to membrane potentials/
    neuronal impulses.
- Three major types ofcones (RGB). (Note that the peaks of absorbance
    curves do not correspond to pure colors.)
- Trichromatic theories (Newton, Young, Helmholtz) vs. Opponent color
    theories (Goethe, Hering). The earliest physiological stage is more
    trichromatic, whereas higher stages have opponent-like features.
- Biological, evolutionary significance of color perception.
    Plants, fruits, flowers. Only limited species (insects, birds, and some
    mammalians) have color perception.
- Complete process of color production. Light source -> reflectance of
    surfaces -> physiological optics of eyes -> photo receptors -> peripheral
    and central nervous system -> mind.
    Cf. fMRI study of color and color afterimages (Sakai, et al. 1995).
- Thus, colors exist (if in any sense) over the chained-sequence from the
    environment to the eyes to the brain. 
 
3. Quantitative assessment of color perception.
- Relationship between receptors' responses and phenomenological colors.
- Metamer, Grassmann's principles. One can quantify, add, subtract, and cancel.
- Linear transformation, and negative color mixture.
- CIE-RGB system.
 
4. Colors in relation to the world.
- Metamer, fMRI evidence for brain activity, color afterimages, synesthesia,
    and color blindness. All these indicate that colors do not merely exist in
    the physical world. Indeed, what is normal and what is color blind are
    totally dependent upon the physiological color channels, i.e. the
    absorbance functions of receptors.
- Subtypes of color blind. Cortical color blind.
- Color perception in animals. Sensitivity to Ultra violet in bees. Sensitivity
    to optical polarization in the cattlefish and the octopus.
- Environmental aspects of color. Aperture color, Ganz Feld, surface color,
    volumetric color, transparency, translucency, burning, etc.
 
5. Illusions and effects.
- Assimilation and contrast.
- Afterimages.
- Completion and filling-in.
- Effects of equiluminance.
- McCullough effect.
- Hermann grid.
- Mach's book.
- Purkinje phenomenon.
 
6. Development of color perception, Color and language.
- Development in the human. Pretty early. Qualitatively same as adults
    at 1-3 months of age.
- Yes, sensitivity is still low(discrimination threshold is high).
- Relatively premature for yellow-Blue discrimination.
- Color categories exist before acquisition of language.
- Color and language. Language precedes perception? (Sapia-Whorf's
    Hypothesis).
- Brown and Lindsay (2001): World-wide correlation between the level of UV-B
    and color vocabulary for blue, green and black . Perhaps related to UV-B
    effect of lens aging. Thus, a case of perception defines language?
 
References
Palmer, S, E. (1999) Vision Science: Photons to Phenomenology. Cambridge, MIT
  Press. Chapter 3, 94-142.
Jameson, D. (1972) Theoretical issues of color perception. In Handbook of
  Sensory Physiology, VII/4, New York, Springer, 381-412.