Quantum phase space from string solitons

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 soliton (0-brane) as the quantum phase space of a point particle. The $\sigma$ model is slightly noncritical 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.