We will describe in two articles ("Sense of self and psychosis", 1 and 2) the theoretical basis and the methodology of a new therapeutic group approach called amniotic therapy, which aims to improve the sense of self of psychotic patients. In this first article we explore the role of the surface of the body and its early sensorimotor interactions in the processes of self/other identification and differentiation. We propose that these processes have common origins, the body surface and its interactions, but different destinies, depending on where the body's surface is projected. When it is projected intrapsychically we have differentiation, and when it is projected externally onto the body's surface of the other, we have identification. Identification is a reciprocal process, in which the self's and the other's surfaces mutually contain each other and co-create a shared field. The neural correlates of identification and differentiation are discussed. The second article, which follows, describes amniotic therapy and explores a single case study.