Close your eyes. Do you see anything? Probably the first thing we answer is nothing, or darkness. A darkness that we usually associate with blackness.
But let’s close our eyes again and let’s be careful, is what we see really black? The truth is that what we see is rather a grayish color, the eigengrau, which we are going to talk about in this article.
What is the Eigengrau and why is it a false color?
We call eigengrau the color we perceive when we keep our eyes closed or we are in the most complete darkness, this color being less dark than the color that corresponds to black.
It is a dark gray color, close to black but curiously and despite being perceived in the absence of light is clearer than an object of this last color in full light. The perceived gray intensity may be slightly different depending on the person. In fact the term in question means intrinsic gray or gray own in German. It is considered that this term was investigated and popularized by Gustav Theodor Fechner, known for his important role in the genesis of psychophysics and the measurement of human perception.
Its perception is considered a phenomenon generated by the retina or its nervous connections with the brain, or product of the action of this. However, it has been observed that the perceived color is not completely stable. As time passes and we keep our eyes closed, the gray gradually appears to become clearer or even perceptions of color may appear.
Explanation of your perception when closing your eyes
The perception of eigengrau color may seem strange if we bear in mind that in reality we should not be able to detect anything with closed eyes or in complete darkness, being diverse the explanations that have been tried to offer on the scientific level.
1. General interpretation
From the first investigations of Fechner was suspected and considered that this perception arose as a kind of residue or background noise of neuronal activity. Even with closed eyes, the different nerves remain active and discharge, generating neuronal activity in the absence of light that the brain is not able to separate from a true perception of luminosity. It would therefore be the product of nervous activity, something that in fact is true to a greater or lesser extent.
2. Isomerization of rhodopsin
Another theory that seeks to deepen the cause of the perception of eigengrau links this perception with the isomerization of rhodopsin, the type of pigment linked not to the perception of color but to the perception of movement and luminosity, allowing vision in the dark and in the gloom.
Finally, another of the main explanations links the perception of this grayish tone especially with the formation of neuromelanin. It is a photosensitive pigment that is produced by the oxidation of dopamine and noradrenaline.
This production takes place in different areas of the brain, especially in the substantia nigra, the locus coeruleus, the protuberance or the cranial vagus nerve.
Linkage with hallucinatory phenomena
The eigengrau and its perception have been linked to the existence of hallucinations, considering in fact a hallucinatory phenomenon of biological, physiological and non-pathological type. The reason for this consideration is the fact that deep down you would be perceiving something that does not really correspond to an external reality.
Some authors also link the perception of this color with a different hallucinatory phenomenon: the appearance of hypnagogic and hypnopompic hallucinations.
In both cases we would be before perceptions without object and variable complexity that usually occur in moments of transition between different states of consciousness, specifically the passage from wakefulness to sleep (hypnagogic hallucinations) or vice versa (hypnopompic hallucinations), and that do not consider pathological product of imbalances between the activation and deactivation of different processes and networks in the process of falling asleep and waking up (also called physiological hallucinations).