Eigengrau: the hallucinating color that you see when you close your eyes

Close your eyes. What do you see? Probably the first thing we answer is nothing, or darkness. Darkness that is generally associated with darkness.

But let’s close our eyes again and take a closer look, is it really black what we’re seeing? The truth is that what we are seeing is rather a gray color, the eigengrau, What we will talk about in this article.

    What is eigengrau and why is it a false color?

    We call eigengrau al ‘ color we perceive when we keep our eyes closed or in complete darkness, This color is less dark than that corresponding to black.

    It is a dark gray color, close to black but curiously and despite the perception in the absence of light, it is lighter than an object of this last color in full light. The intensity of perceived gray may be slightly different from person to person. In fact, the term in question means intrinsic gray or clean gray in German. This term would have been researched 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 to be a phenomenon generated by the retina or its nerve connections with the brain, or a product of its action. However, it has been observed that the perceived color is not completely stable. As time goes on and we keep our eyes closed, the gray gradually seems to become lighter or even color perceptions may appear.

    Explanation of their perception by closing your eyes

    The perception of the color eigengrau may seem strange when you consider that in reality we should not be able to detect anything with our eyes closed or in complete darkness, being various explanations that have been tried to offer respect to the scientific level.

    1. General interpretation

    As early as Fechner’s early research, it was suspected and considered that this perception presented itself as some sort of residue or background noise from neuronal activity. Even with closed eyes, the various nerves remain active and perform discharges, generating neural activity in the absence of light that the brain he is unable to separate himself from a real perception of luminosity. It would therefore be the product of nervous activity, which is in fact more or less true.

    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 light, Allowing vision in the dark and twilight.

    3. Neuromelanin

    Finally, another of the main explanations links the perception of this grayish tone, in particular with the formation of neuromelanin. It is a photosensitive pigment produced by the oxidation of dopamine and norepinephrine.

    this production it takes place in different areas of the brain, Especially in the substantia nigra, locus coeruleus, bulge, or cranial vagus nerve.

    Link with hallucinatory phenomena

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

    Some authors also link the perception of this color to another hallucinatory phenomenon: the appearance of hallucinations. hypnagogic and hypnopompic.

    In either case, we would be faced with perceptions without an object and of varying complexity which usually arise in moments of transition between different states of consciousness, in particular the transition from wakefulness to sleep (hypnagogic hallucinations) or vice versa (hallucinations). hypnopomic), and this should not be considered pathological but the product of imbalances between the activation and deactivation of different processes and networks during sleep and awakening (also called physiological hallucinations).

    Bibliographical references:

    • Bynum, EB; Brown, AC; King, RD and Moore, TO (2005). Why darkness matters: the power of melanin in the brain. African-American Images: Chicago, Ill.
    • Bynum, EB (2014). Black Light Awareness: The Path Through Our Neural Substrate. Psychodiscours, 48 ​​(2).
    • Fechner, GT (1860). Elements of psychophysics. Leipzig: Breitkopf and Härtel.
    • Nieto, A .; Torrero, C. and Sales, M. (1997). Comparative study of the density of neuromelanin in the locus ceruleus and dark matter in certain mammals, including humans. Journal of Psychopathology, 17 (4): 162-167. CSIC.

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