This paper, which addresses the issue of representation as an internal construct corresponding to an external abstract configuration, attempts to extend A. A. DiSessa's phenomenological primitives to mathematics (particularly to the notion of circle). Various acceptations of the word representation are examined, using the notion of a circle as an example. Primitive conceptions are presented together with two tasks aimed at probing their presence or evolution. Two computer programs (three-ring puzzle and moving-around-the arc) which bring forward the development of primitive conceptions are described as is a small-scale investigation in which the programs were used. Negative results obtained from the investigation are analyzed in view of the intrinsic difficulty of pinning down the elusive mental constructs. The importance of the research project as computers start to be used to enlarge children's universe of experimentation (micro-world) is stressed. (Author/JN)