We appreciate the opportunity to participate in Journal of Neurologic Physical Therapy's Clinical Point of View and for the chance to respond to the Commentary on our article. We agree with the authors of the Commentary that our study "participants may not represent the typical patients seen by physical therapists." We recruited participants with mild to moderate chronic motion sensitivity (CMS) on the basis of self-report and the motion sensitivity quotient. Previously, we used the term "subclinical" to describe our participants because they did not have a medical diagnosis attached to their CMS and were not seeking clinical intervention.1 Rather, they were simply avoiding certain activities that provoked or exacerbated their symptoms. The APTA Vision Statement for the Physical Therapy Profession is "Transforming society by optimizing movement to improve the human experience."2 Our current position is that people with "subclinical" CMS may be able to realize this "improvement" through physical therapy intervention.

Regarding intervention, we understand the interest in how gaze stability exercises might reduce motion sensitivity and visually provoked postural instability. The authors of the Commentary accurately described the dual-task nature of our gaze stability exercises and proposed plausible explanations for the observed changes in postural stability. Our assumption was that participants with CMS were overreliant on visual cues for maintaining postural stability.3 The "infinite tunnel" immersive virtual reality environment provided participants with strong visual input that they were moving in an anterior direction. Our objective was to reweight the sensory input by directly stimulating the vestibular system through prolonged and progressive gaze stability exercises. Whitney et al4 described the emerging evidence regarding the capacity of the CNS to compensate for vestibular dysfunction and reweight sensory inputs in order to improve function. Although emphasis was placed on the neural mismatch model,5 another consideration for a possible reweighting effect is Riccio and Stoffregen's6 ecological theory of motion sensitivity and postural instability concerning perception and control of orientation and self-motion. Habitual practice of self-generated head motion while standing may have conditioned our participant's postural responses in the presence of challenging visual stimuli.

In addition, the authors of the Commentary had questions concerning our results and the clinical meaningfulness. We compared the mean percent change ([post - pre]/pre) x 100) between 2 groups and found that mean percent change was 117% in the intervention group versus 35% in the sham group. This finding indicates that the improvement was significantly higher in the intervention group than in the sham group. The sham group had a higher mean performance at pretest and less improvement at posttest; however, the intervention group had lower mean performance at pretest and significantly more improvement at posttest.

Finally, we agree with the Commentary statement that "clinicians should be cautious in generalizing the results of this study to patient populations with more severe motion sensitivity," given that was not our target population. In addition, we identified several limitations in our study and recognize that more research is needed before generalizations can be made with respect to mechanisms and intervention protocols for this population. We hope that our article and the related Commentary will generate productive discussion in the neurologic physical therapy community.

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