Tilt-Induced Anisotropic to Isotropic Phase Transition at v=5/2

A modest in-plane magnetic field B(parallel to) is sufficient to destroy the fractional quantized Hall states at v = 5/2 and 7/2 and replace them with anisotropic compressible phases. Remarkably, we find that at larger B(parallel to) these anisotropic phases can themselves be replaced by isotropic compressible phases reminiscent of the composite fermion fluid at v = 1/2. We present strong evidence that this transition is a consequence of the mixing of Landau levels from different electric subbands. We also report surprising dependences of the energy gaps at v = 5/2 and 7/3 on the width of the confinement potential.