  In an ideal two-component two-dimensional electron system, particle-hole
symmetry dictates that the fractional quantum Hall states around $\nu = 1/2$
are equivalent to those around $\nu = 3/2$. We demonstrate that composite
fermions (CFs) around $\nu = 1/2$ in AlAs possess a valley degree of freedom
like their counterparts around $\nu = 3/2$. However, focusing on $\nu = 2/3$
and 4/3, we find that the energy needed to completely valley polarize the CFs
around $\nu = 1/2$ is considerably smaller than the corresponding value for CFs
around $\nu = 3/2$ thus betraying a particle-hole symmetry breaking.
