Recalibration of vestibular reafference alters the recovery response to a platform perturbation

This thesis presents three complementary experiments that aim to investigate the sensorimotor recalibration of vestibular reafference for platform perturbation recovery responses. Previous work has demonstrated that visual feedback is used to recalibrate the vestibular reafference used to control vestibulo-ocular reflexes as well as navigation. However, less work has examined the visual calibration of vestibular feedback for postural control. During a platform perturbation, vestibular feedback is thought to have very little contribution to the initial components of recovery responses and is largely involved in re-establishing postural equilibrium following recovery responses. In experiment I, we investigated whether vision could be used to alter how vestibular reafference was used for re-establishing equilibrium following a perturbation. We were able to show that after changing the vertical interpretation of a GVS- altered vestibular signal using visual references, participants became realigned toward the cathode following GVS removal, suggesting recalibration of the vestibular signal. Interestingly, vision was unable to alter the vestibular influence on initial perturbation responses. Previous work has shown that multiple trial exposures may be necessary to demonstrate recalibration. Therefore, experiment II examined whether visual feedback provided during a platform perturbation could recalibrate the contribution of vestibular reafference to early components of the recovery response. We demonstrated that vestibular contributions to early components of perturbation responses could be recalibrated but that the recalibration observed was likely mediated by somatosensory feedback rather than vision. Sensory integration work has shown the importance of attending to the sensory feedback provided for improving postural control. In experiment III, we aimed to determine whether instructions to specifically attend to somatosensory feedback for realigning posture during multiple platform perturbations could improve the recalibration of vestibular reafference on initial perturbation responses. Participants did not show improvements in their ability to recalibrate vestibular feedback during perturbation responses with added instructions to attend to somatosensory feedback. This may result from the fact that our postural control task did not merit the allocation of additional attention resources in our young healthy population. Together, our data show a task dependent recalibration of vestibular reafference for postural control. The following experiments provide further understanding into the integration of visual and vestibular feedback for postural control and how a change or decline in sensory feedback might be compensated for. This work may provide merit for rehabilitation strategies to take advantage of using intact or reliable sensory feedback to recalibrate sensory feedback that had been altered or declined, as is often the case for clinical and older adult populations.