Stepping in Place While Voluntarily Turning Around Produces a Long-Lasting Posteffect Consisting in Inadvertent Turning While Stepping Eyes Closed

Figure 3

Coordinated head and shoulder movements. Angle described by the head (solid lines) and shoulders (dashed lines) mediolateral axis in a time period of 10 s during podokinetic stimulation (Pod Stim, (a)), PKAR (b), voluntary turning (Vol Turn, (c)), and its posteffect (vPKAR, (d)). During platform rotation, the body was kept almost fixed in space while head and shoulders showed minor left and right angular shifts. During voluntary turning (c) and during the two posteffects (b and d), head and shoulders continued to rotate in the horizontal plane, so that, in addition to their left and right yaw shift (a), the angle described by these segments continued to increase over time. The large differences in the y-scale amplitude between panel (a) and panels (b), (c), and (d) accommodate for the differences in the cumulative angle. The time lags between head and shoulders traces are reported in panel (e) for each subject. The 10 ms interval between the data points depends on the acquisition frequency; in many cases, several points coincide. There were no obvious differences across conditions.

(a)

(b)

(c)

(d)

(e)