The starting point for this thesis is the juxtaposition of two works of art from the 1960s: Study for ‘Skin’ I, a print-drawing from 1962 by Jasper Johns, and the photograph Self-Portrait as a Fountain from 1966 by Bruce Nauman. Viewing these works in conjunction with Palaeolithic hand stencils, the marking of threshold events emerges as a theme. Resonant material is then assembled and studied: Surrealist texts and photography, or the use of photography, by André Breton, Claude Cahun and Man Ray; the medical theses of psychiatrists François Tosquelles and Jean Oury; and works on prehistoric art by Georges Bataille and André Leroi-Gourhan. The marking of threshold events at two nesting scales of analysis – the evolutionary emergence of the human species; and the psychotic onset of hallucination and delusion – is examined. Echoes are found to resound in a third register– in the neurological events that give rise to consciousness and dream experience. Consideration of the Johns drawing and Nauman photograph in these terms is proposed.