Close your eyes. What do you see? Probably the first thing we answer is nothing, or darkness. A darkness we usually associate with blackness.

But let’s close our eyes again and take a good look, is it really blackness that we see? The truth is that what we see is rather a greyish colour, the eigengrau , which we are going to talk about in this article.

What is eigengrau and why is it a false colour?

We call eigengrau the colour we perceive when we keep our eyes closed or are in complete darkness , being less dark than the colour corresponding to black.

It is a dark grey colour, close to black but which, curiously, despite being perceived in the absence of light, is lighter than an object of the latter colour in full light. The intensity of the grey perceived can be slightly different depending on the person. In fact the term in question means intrinsic grey or own grey in German. It is considered that this term was researched and popularized by Gustav Theodor Fechner, known for his important role in the genesis of psychophysics and the measurement of human perception.

Their perception is considered a phenomenon generated by the retina or its nerve connections to the brain, or a product of the action of the brain. However, it has been observed that the colour perceived is not totally stable . As time goes by and we keep our eyes closed, the grey gradually appears to become lighter or even colour perceptions may appear.

Explanation of your perception when you close your eyes

The perception of the colour eigengrau may seem strange if we consider that in reality we should not be able to detect anything with our eyes closed or in complete darkness, and there are various explanations that have been tried to offer on a scientific level.

1. General interpretation

Even in Fechner’s early research, this perception was suspected and considered to be a kind of residue or background noise of neuronal activity. Even with the eyes closed, the different nerves remain active and carry out discharges, generating neuronal activity in the absence of light that the brain is not capable of separating from a true perception of luminosity . This would therefore be the product of nerve activity, something that is in fact true to a greater or lesser extent.

2. Isomerization of rhodopsin

Another theory that seeks to delve into the cause of the perception of eigengrau links this perception to 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 darkness and half-light.

3. Neuromelanin

Finally, another of the main explanations links the perception of this greyish tone especially with the formation of neuromelanin . This 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 cranial bump or the cranial vagus nerve.

Link to hallucinatory phenomena

Eigengrau and its perception have been linked to the existence of hallucinations, being considered in fact a hallucinatory phenomenon of biological, physiological and non-pathological type . The reason for this consideration is the fact that deep down we would be perceiving something that does not really correspond to an external reality.

Some authors also link the perception of this colour with a different hallucinatory phenomenon: the appearance of hypnagogic and hypnopompic hallucinations .

In both cases, we would be faced with perceptions without object and of 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 which are not considered pathological but the 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).

Bibliographic references:

  • Bynum, E. B.; Brown, A. C.; King, R. D., & Moore, T. O. (2005). Why Darkness Matters: The Power of Melanin in the Brain. African American Images: Chicago, Ill.
  • Bynum, E. B. (2014). Dark light consciousness: the Pathway Through Our Neural Substrate. Psychdiscourse, 48 (2).
  • Fechner, G.T. (1860). Elemente der Psychophysik. Leipzig: Breitkopf und Härtel.
  • Nieto, A.; Torrero, C. and Salas, M. (1997). Comparative study of neuromelanin density in the locus ceruleus and the substantia nigra in some mammals, including man. Journal of Psychopathology, 17 (4): 162-167. CSIC.