My question, in other words, is: when we see an object of different colours, does every colour cause the same frequency in the corresponding activated cone?
Does every qualia (yellow, red and so on) have a particular frequency and/or amplitude, or all the cones fire with the same frequency (of course, when the stimulus is kept constant and regular)?
The difference between, say, the red and the green is just qualitative in the retina and in the brain, or it might be quantified?
Thanks!
your question "The retina contains L cones, M cones and S cones: when they are activated, do they fire with the same frequency?"
No. Check out the following chapter if I have understood your question correctly, e.g. figure 14. The three main types of cone have different selectivities for any given wavelength of light, which translates into different voltage responses.
http://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/photoreceptors/
(note, also "fire" is not the usual term for cones, since they don't generate action potentials).
your question "The retina contains L cones, M cones and S cones: when they are activated, do they fire with the same frequency?"
No. Check out the following chapter if I have understood your question correctly, e.g. figure 14. The three main types of cone have different selectivities for any given wavelength of light, which translates into different voltage responses.
http://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/photoreceptors/
(note, also "fire" is not the usual term for cones, since they don't generate action potentials).
Dear Stephen, thanks for the clear response! thanks a lot!
Thus, it means that every one of the three types of cones (apart from their peculiar sensitivity for specific wavelengths), when is activated, displays a different voltage response?
It means, in theory, that, if you detect the voltage response from a cone, you may guess which color is the subject watching?
Do you know which are the single voltage responses of every type of cone, when exposed to stimuli of the same intensity?
Thanks again!
Dear Stephen,
what about the optic nerve? when I see a red light, the spike frequency and amplitude measured in my optic nerve are different than the ones measured when I see a green light? Is it possible to answer to this question?
Thanks!
All photoreceptors hyperpolarize (that results in a decrease in neurotransmitter release) when they are activated. Each cone type will have different amounts of absorbtion depending on the wavelength. The graded potential of each cone type is dependent on the wavelength of the stimulus and the absorbtion spectra of the photoreceptor.
Baylor, Nunn, and Schnapf (1987) reported the membrane currents from single outer segments from Macaca monkeys. Spectral sensitivity of the cones of the monkey Macaca fascicularis. Journal of Physiology 390, 145-160.
You can find values for these currents as well as individual cone spectra (and a at the Color Vision and Research Laboratory website (www.cvl.org) in spreadsheet form (as well as a host of other absorption, electrophyiological, and psychophysical measures for cones.
Hi Arturo, I think the Baylor et al paper gives you the current data.
"It means, in theory, that, if you detect the voltage response from a cone, you may guess which color is the subject watching?"
Not likely -- even in theory if you had the perfect voltage response, as the "tuning curves" are unimodal bumps, there's normally two wavelengths (either side of the peak selectivity) that could generate the same response.
Re: colour coding in the optic nerve, that's a different issue, and what you often see if colour-opponency, e.g. red-green differences. check out this chapter for details:
http://webvision.med.utah.edu/book/part-ii-anatomy-and-physiology-of-the-retina/ganglion-cell-physiology/
Qualia is not restricted to these cells for even the blind can have an experience of a colour, without actually seeing the colour.
there is a series of seminal papers from Jacobs and others which gave novel colours to Animals, just by changing their cones..
Thus, dear Contzen, I think you are right, when you highlight the role of structures other than peripheral receptors in visual perception.
But, this time, I'm interested in trying to understand whether different colours elicit in our nerves recognizable, typical, pathognomonic patterns...
Colour is not a point property but depend on surface perception and the colour of a certain surface patch do depend on the colour of the neighboring surface patches. So colour perception is a very complex process. The colour perceived at a point not only depend on the stimulation of the cones at that point on the retina but on the stimulation of the cones on the whole retina and in relation with many other visual processes.
There are many experiements that have demonstrated this. In the image below, the top surface has been illuminated by very different light sources that change drastically the spectrum of the light that are reflected by each colour patches but in spite of these drastic changes we perceive the colour of these patches almost as the same. The perceived colour on the left image being very similar to the perceived colour on the right image.
The Kanitza image show that the triangle that is perceived has a lighter white than the background in spite of the fact that there is no change in the local stimulation of the cones inside or outside the triangle. Here the surface perception trigger a global uniformization of the perceived white at a brighter level than the outside background. Not only is colour not a local property but what is a surface border is not a local property on the retina. All aspects of what is perceived visually are global as the object out there. The visual process is organic in the sense that the global aspects determine the perception of the local aspects. The local aspects are never perceived outside of their global context.
Dar Louis,
I understand what are you saying. It's in touch with:
https://www.researchgate.net/publication/299844504_GIBSON%27S_ECOLOGICAL_THEORY_OF_PERCEPTION_TOPOLOGY_MATTERS
I appreciate your "gestalt" perspective, and, to be honest, I join it, but, this time, I wanted to be more concerned with more "classical" frameworks, avoiding holistic approaches (that, nevertheless, I like very much).
This time, I want (if it's possible) just a quantitative correlation between the light and the brain wavelengths!
Preprint GIBSON’S ECOLOGICAL THEORY OF PERCEPTION: TOPOLOGY MATTERS
Adding my comments to this question. my self worked on two frequencies which stimulate L and M cones. The contribution of L and M cone amplitudes is different at 12 Hz and 30 Hz flicker frequency is different. at 12Hz frequency the amplitudes of both cones have similar responses but they have different responses at 30Hz. M cones hardly respond to this high frequency. you can also looka t my paper "L- and M-cone input to 12Hz and 30Hz flicker ERGs across the human retina''.
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