  We tested the ability of human observers to discriminate distinct profiles of
spatially dependant geometric phases when directly viewing stationary
structured light beams. Participants viewed polarization coupled orbital
angular momentum (OAM) states, or ``spin-orbit'' states, in which the OAM was
induced through Pancharatnam-Berry phases. The coupling between polarization
and OAM in these beams manifests as spatially dependant polarization. Regions
of uniform polarization are perceived as specifically oriented Haidinger's
brushes, and study participants discriminated between two spin-orbit states
based on the rotational symmetry in the spatial orientations of these brushes.
Participants used self-generated eye movements to prevent adaptation to the
visual stimuli. After initial training, the participants were able to correctly
discriminate between two spin-orbit states, differentiated by OAM $=\pm1$, with
an average success probability of $69\%$ ($S.D. = 22\%$, $p = 0.013$). These
results support our previous observation that human observers can directly
perceive spin-orbit states, and extend this finding to non-rotating beams, OAM
modes induced via Pancharatnam-Berry phases, and the discrimination of states
that are differentiated by OAM.
