Postural control in quiet standing with a concurrent cognitive task in psychotic conditions.

Differences in postural control and performance between psychotic patients and healthy subjects were investigated using a dual task paradigm. Center of pressure (CoP) data and whole-body kinematics of the center of mass (CoM) were recorded during quiet standing with and without a backward counting task. Dual task response was similar in both groups: the magnitude of CoM-migration did not change, while CoP-CoM magnitude, a measure related to ankle joint torque, and CoP-frequency both increased. The magnitudes of migration for CoM and CoP-CoM were greater in patients during both conditions, while CoP-frequency was similar to control subjects. Our results suggest that exaggerated ankle joint torque relative to CoP-frequency caused greater postural sway in patients during both conditions.