  We have measured the in-plane anisotropy of the vortex mobility in a thin Pb
film with a square array of antidots. The Lorentz force, acting on the
vortices, was rotated by adding two perpendicular currents and keeping the
amplitude of the net current constant. One set of voltage probes was used to
detect the vortex motion. We show that the pinning landscape provided by the
square antidot lattice influences the vortex motion in two different ways.
First, the modulus of the vortex velocity becomes angular dependent with a
lower mobility along the diagonals of the pinning array. Second, the vortex
displacement is preferentially parallel to the principal axes of the underlying
pinning lattice, giving rise to a misalignment between the vortex velocity and
the applied Lorentz force. We show that this anisotropic vortex motion is
temperature dependent and progressively fades out when approaching the normal
state.
