Two possible reasons could be explained as follows. First, although we encouraged our subjects to practice eye-head coordination exercise at the frequency high enough to produce the error signal, most elderly, however, were not able to comply with this protocol and tended to perform the exercise at lower frequency. In consequence, the intensity of the eye-head coordination exercise may not be sufficient enough to produce the adaptation of the vestibular system. Herdman suggested that the slippage of images on retinal stimulus was the best stimulus to induce vestibular adaptation. The patients may experience an increase in symptoms and must be encouraged to continue the exercise without stopping. Second, our study evaluated the VOR performance at fixed frequency of 1 Hz. As the VOR was frequency-dependent, it was possible that the change in VOR gain occurred at lower frequency related to practice frequency so we did not see the change at 1 Hz. This result agreed with Lisberger and associates that the vestibular adaptation was frequency-dependent. If the system was adapted at a specific frequency, the VOR gain would improve most at that frequency.