The Impact of Attentional Focus on Sensory Reweighting for Postural Control in the Aging Adult

Abstract

This dissertation aims to understand how attention can be used to improve sensory integration for postural control. Decades of research have been done using visual manipulations to study how healthy and clinical populations resolve multisensory (vision, vestibular, and somatosensory) mismatches to maintain postural stability. Postural control is a complex motor skill that requires accurate integration of multiple senses to maintain body alignment and orientation with respect to the environment. Age-related decline in visual, vestibular, and somatosensory acuity increases the risk for falls, and these sensory declines can be identified by assessing sensory reweighting. Sensory reweighting is the process in which the nervous redistributes the reliance, or "weight," on the sensory inputs to achieve postural stability. While the literature on sensory manipulation on postural control and fall risk has uncovered a wealth of knowledge on sensory reweighting for balance, it has neglected to identify how sensory reweighting can be improved. At the same time, motor learning literature has demonstrated the importance of focus attention during balance training to improve postural control. However, rudimentary analyses such as duration of balance and sway variability in this literature have limited deeper examination of the underlying neural mechanisms affected by focus of attention. This dissertation aims to bridge the gap between the two works of literature by implementing sensory manipulation techniques on posture using the latest technologies in virtual reality (VR) head-mount display (HMD) with motion capture and electroencephalography (EEG) recordings to study how different focuses of attention help resolve multisensory conflicts. In aim one, forty-two healthy adults participated in the study that used VR manipulation to induce a multisensory conflict. Participants were tasked to maintain upright stability on a rocker board while given different instructions on where to focus their attention. Instructions included focusing on keeping the rocker board leveled (external focus), focusing on keeping feet leveled to each other (internal focus), and focusing on staying as still as possible (control). This study revealed an immediate improvement in postural stability when instructed with external focus compared to control. This improvement was also associated with a significant decrease in visual weighting. Additionally, this aim revealed an immediate change in cortical activity within the frontal and occipital regions of the brain as identified by EEG recordings when participants are instructed to use external focus and internal focus. In aim two, twenty-eight healthy adults participated in the crossover study that demonstrated order effects when multiple instructions of attentional focus were given to the same participant for postural stability and visual reweighting. This study showed that the effects of external focus on postural stability and visual reweighting are greater when external focus is used before internal focus. However, the effects of external focus were nullified when used after using internal focus. Furthermore, the order of the instructions may have corresponded with a recency bias regarding how the participant perceived the effectiveness depending on when they received the attentional focus instruction. Guided by the findings from aims one and two, aim three recruited twenty-seven older adults to participate in a single-session balance training using repeated exposure to VR manipulation that challenged their balance on a rocker board. The older adults were randomized into one of the three groups: external focus, internal focus, and control group. The external focus group did not demonstrate an immediate reduction in visual weighting as found in aim 1. However, the external focus group did demonstrate better immediate postural stability when compared to the internal focus groups. Both external and internal focus groups revealed a significant improvement in visual weighting and postural stability across training blocks, suggesting a potential role of attentional focus on postural control adaption to repeated VR exposure. This dissertation was one of the first studies to investigate how the attentional focus impacts sensory reweighting and postural control in young and older adults using VR HMD. This project also established a VR experimental paradigm that can be used to study the focus of attention and the resolution of multisensory mismatch. With the increased use of VR for balance training and rehabilitation, this project is at the forefront of utilizing VR HMD technology to expose underlying sensory mechanisms for postural control. Results from this study can guide future rehabilitation and balance training interventions by identifying how attention should be directed during training.