  We report the first study of the dynamics of point defects, mono and
di-vacancies, in a confined 2-D colloidal crystal in real space and time using
digital video microscopy. The defects are introduced by manipulating individual
particles with optical tweezers. The diffusion rates are measured to be
$D_{mono}/a^{2}\cong3.27\pm0.03$Hz for mono-vacancies and
$D_{di}/a^{2}\cong3.71\pm0.03$Hz for di-vacancies. The elementary diffusion
processes are identified and it is found that the diffusion of di-vacancies is
enhanced by a \textit{dislocation dissociation-recombination} mechanism.
Furthermore, the defects do not follow a simple random walk but their hopping
exhibits memory effects, due to the reduced symmetry (compared to the
triangular lattice) of their stable configurations, and the slow relaxation
rates of the lattice modes.
