Unilateral displacement in the olfactory sense: a manifestation of the unilateral neglect syndrome.

Unilateral neglect is a syndrome primarily occurring with right hemisphere--particularly right parietal lobe--brain damage and involving the failure to respond to stimuli presented to the left side of the body and space. Unilateral displacement (a less severe manifestation of the neglect syndrome) involves the accurate identification of a stimulus, but the displacement or mislocalization of that stimulus to the opposite side of the body and space. This study investigated two major theories of unilateral neglect utilizing the primarily ipsilaterally innervated olfactory sense. The sensory theory states that unilateral neglect is due to a diminished sensory input, whereas the representational theory states that it is due to a disordered internal representation which is not dependent on sensory input. Results revealed that right hemisphere lesion patients with left unilateral neglect exhibited a significantly greater number of displacements in their left nostril on olfactory double simultaneous stimulation, consistent with the representational theory.