From photons to opponent codes

A photon arrives with a wavelength. What leaves the retina is a comparison. Each preset below runs the same machinery to make a different point.

Demonstrations

Cone sensitivity

Probability that a cone of each class absorbs an arriving photon.

Photons arriving at the outer segments

Color drains at the moment of absorption. After that the cone has only a count.

Light A

Light B

Two spectra the eye cannot separate

A test light, and a mixture of three narrow primaries solved to match it on all three cone classes.

One flash, followed through four cells

Cones and bipolar cells respond with graded membrane potential. Spikes begin at the ganglion cell.

Stimulus against the adapted background

The gray field sets each cone's adapted level. The patch is what changes.

Ganglion cell output

Maintained rate shown dashed. The signal is the excursion, in either direction.

L against M, across many stimuli

Every dot is one patch. Broadband changes are marked separately.

Why subtract at all

The same dots, projected onto the two axes.

Wavelength

Photon rate

Wavelength, light B

Photon rate, light B

M-cone peak

Test wavelength

Test bandwidth

Flash wavelength

Flash strength

Patch wavelength

Patch spectral peak

Patch broadband level

Illumination on the whole scene

Tint photons by wavelength Wire the ganglion cell as center vs mixed surround Neutral flash instead of monochromatic Show raw L − M alongside cone contrast Arrow keys step through the demonstrations; space pauses.