Double Filters Allow for Tetrachromatic Vision in Humans

Double Filters Allow for Tetrachromatic Vision in Humans
Schematic of our filter-based cone partitioning method, consisting of two distinct transmission filters. Plot (a) shows the spectra of a sample pair of metamers, (i) and (ii), which appear as the same purple color and were experimentally generated using two different displays (CRT and LCD). The measured transmission spectra of filters 1 and 2 are given in (b); (c) shows a magnified view of one of the transition regions of the filters, demonstrating their angular response. The color samples in (d) represent the perceived colors of spectra (i-iii), where spectrum (iii) is CIE D65 white light, in the absence of any filters. The samples in d(i) and d(ii) are the same color (i.e., they are metamers), and d(iii) is pure white. (e) and (f) show the colors corresponding to spectra (i-iii) as observed through filters 1 and 2; spectra (i) and (ii) no longer map to the same color. Samples e(iii) and f(iii) are approximately the same perceived color, which is a consequence of the white-balance design constraint that is enforced to limit color clashing. Credit: arXiv:1703.04392 [cs.CV]

Humans eyes have three types of cone cells behind them that differentiate color. The cones do their work by responding to the difference in wavelength of the incoming light. By doing this, some cells reacts to blue, some to green and some to red. This is a process that discards a significant amount of spectral information. And this vision is known as tetrachromatic vision. To enhance human color vision i.e. tetrachromatic vision, scientists have developed a new pair of glasses.

These new glasses allow a person (with color blindness) to have tetrachromatic vision. To develop this glasses, scientists developed two types of filters (One filter for a single eye). These filters remove some parts of the blue light spectrum. When the filters fitted into a frame and worn like regular glasses, the wearer is able sees the colors that are normally hidden—metamers.

Double Filters Allow for Tetrachromatic Vision in Humans
(a) Schematic of the metamer generation setup; (i) is a 50/50 beam splitter, and (ii) is the viewing plane. (b) The photograph was taken at place (ii) in the schematic. (c) Purple metameric blocks of color generated by the monitors through no filter, filter 1, and filter 2, respectively, showing that the metamers can be distinguished using either filter 1 or filter 2. Credit: arXiv:1703.04392 [cs.CV]
Adding spectrum identification to color blind eyes allows for seeing more of what is already there. This is exactly what happened here. With the new glasses, a person is able to look at what appears to be an object that is all the same color, such as purple, and see more colors in it—those normally hidden metamers.

With this new pair of glasses, scientists also found a way of fooling the brain into seeing. It is like there was a fourth type of cone, by wearing glasses with two types of filters. The result is the tetrachromatic vision.

Researchers said, “It is possible to extend the idea used to create their glasses to the other two colors that cone cells process, red and green, to create glasses that offer the ability to see six basic types of colors instead of the normal three. We are planning to start with green. Such glasses might be used to spot counterfeit money or to see a person in the jungle wearing camouflage.”