  In this paper we view the sigma-model couplings of appropriate vertex
operators describing the interaction of string matter with a certain type of
string solitons (0-branes) as the quantum phase space of a point particle. The
sigma-model is slightly non critical, and therefore one should dress it with a
Liouville mode. Quantization is achieved by summing over world-sheet genera (in
the pinched approximation). To leading order in the coupling constant
expansion, the quantization reproduces the usual quantum mechanical commutator.
We attempt to go beyond leading order and we reproduce the generalized string
uncertainty principle.
