2. Relate the responses of chromatically opponent lateral geniculate neurons (De
ID: 182338 • Letter: 2
Question
2. Relate the responses of chromatically opponent lateral geniculate neurons (DeValois et al.) to the color naming experiment of Boynton and Gordon. Be certain to indicate how DeValois et al. transformed the color naming data and the LGN responses so that they could be compared. According to DeValois et al., what determines the color name(s) used to describe a monochromatic light? Be certain to indicate the ranges of wavelengths at which color naming can be predicted from the activity of chromatically opponent cells. Also specify the wavelengths at which color naming cannot be predicted from neural activity and describe the inconsistencies.Explanation / Answer
A detailed analysis was made of the response characteristics of the single cells in a lateral genitculate nucleus of the macaque monkey to understand that how these cells contribute to the visual information. A sample of 147 cells were taken and exposed to equal-energy spectra (presented as diffuesd flashes of monochromatic light) and data was recorded and analysed at three different raidance level covering a range of one log unit.
On the basis of this the cells were divided into two general classes:
1. Spectrally non-opponent cells which response to all wavelengths with either an increase (excitation) or decrease (inhibition) in firing rate.
2. Spectrally opponent cells which respond with an increase in firing rate to some parts of the spectrum and a decrease to other parts.
Opponent cells are again divided in to four parts :
a) red excitatory and green inhibitory (+R-G) (long wavelength)
b) green excitatory and red inhibitory (+G-R) (short wavelength)
c) yellow excitatory and blue inhibitory (+Y-B) (long wavelength)
d) Blue excitatory and yellow inhibitory (+B-Y) (short wavelength)
It doesn't seems possible that there is an essentially unlimited number of different types of cells in terms of their spectral responses, there is strong pshycophysical evidence in terms of limited number of channels upon which color vision is based. If each cell concerned with color vision were transmitting information slightly differenct from every other cell , and the information remain intact throughout the later analyses , then two monochromatic light lying side by side would never appear equal as each would be affecting cells with slightly different responses. That is likewise it is stated that in laterl neural analysis, information is averaged over a number of similiar cells for the determination of color sensation and that the slight quantitative differences among cells represnt random variance in the system.
when the spectral sensitivity curves are compared the agreement is strikigly good over a range of 420 to 670nm, the only significant deviation being 0.3 log unit dip at about 530nm.
when all the pshyco-physical data was compared indicate that non-opponent cells indicate brightness information and opponent cells however carry information about color, the hue of light being determined by relative responses of the 4 types. The staturation of spectral light appears to be related to the differences in responses of opponent and non-opponent cells.
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