eigengrau
...that even in perfect darkness, the retina spontaneously sends signals down the optic nerve, causing a sensation of gray called eigengrau?
...that even in perfect darkness, the <a href="./Retina" id="mwVg" rel="mw:WikiLink" title="Retina">retina</a> spontaneously sends signals down the <a href="./Optic_nerve" id="mwVw" rel="mw:WikiLink" title="Optic nerve">optic nerve</a>, causing a sensation of gray called <i id="mwWA"><b id="mwWQ"><a href="./Eigengrau" id="mwWg" rel="mw:WikiLink" title="Eigengrau">eigengrau</a></b></i>?