Merging of the senses : interactions between auditory and proprioceptive modalities

Abstract

This doctoral work reports the influence of self-generated auditory feedback i.e. movement sofication on motor control, learning and imagery. In its structure, this research work incorporates a detailed literature review, meta-analyses followed by three experimental studies and two futurized perspective articles. Initially, a total of seven systematic reviews and dose-response meta-analyses were performed to evaluate the influence of music-based auditory stimulation therapies i.e. rhythmic auditory cueing, patterned sensory enhancement and movement-sonification on gait rehabilitation, postural stability, movement kinematics in healthy population groups and in individuals affected from neurological disorders such as, Cerebral palsy, Parkinson’s disease, Multiple Sclerosis, and Stroke. The systematic review and meta-analyses adhered to the PRISMA guidelines. In total, 200 studies including 6,164 participants were included in the review studies. The findings from all of these studies were used to understand the efficacy of auditory-motor training interventions and their underlying neurophysiological mechanisms. The findings from these reviews comprehensively demonstrated efficient, cost-effective benefits of music-based auditory stimulation therapies in recovering motor, cognitive and sensory functioning in both healthy and neurologically affected population groups. Moreover, the studies also reported effective auditory-motor training dosages that could be applicable to attain maximum benefits during an intervention. The findings from these review studies were also utilized to derive research questions and hypotheses for the experimental studies performed in this doctoral research work. In the following three experimental studies, our group demonstrated the intricate relationship between auditory-proprioceptive modalities and demonstrated the beneficial influence of self-generated real-time auditory feedback (movement sonification) to facilitate active knee-joint proprioceptive perceptions. Firstly, our group demonstrated the beneficial effects of direct application of sonification on knee re-positioning accuracy. Moreover, in the same experiment we also demonstrated the intricate auditory-proprioceptive interaction during a subliminal step-wise transposition of the auditory feedback’s pitch (±2.6 Hz). Here, subliminal transposition during the performance of a knee re-positioning task led to goal-directed modulation of proprioceptive perceptions in the opposite direction of transposition. Further, in the second experiment, our group demonstrated that an intensive bilateral training with self-produced auditory feedback led to robust enhancements in knee proprioceptive accuracy after 25-30 minutes of training. The enhancements in proprioceptive perceptions were both retainable (without auditory feedback after 15 minutes and 24 hours) and transferrable (on untrained target angles). This experiment for the first time demonstrated the beneficial influence of auditory on intermodal learning. In the third experiment, our group elucidated the influence of self-generated auditory feedback on motor imagery. Here, we demonstrated that performing auditory-guided mental imagery after an auditory-motor training led to enhanced knee-proprioceptive perception as compared to conventional mental imagery i.e. imagining movements without any auditory feedback. Again, the enhancements observed in knee-joint proprioception were both retainable and transferred to untrained angles in the absence of auditory feedback. The findings from these experiments are novel and have immense practicality for application in both musculoskeletal and neurological rehabilitation protocols. Finally, two future perspective articles were included in this dissertation that propose possible applications of different auditory feedback based training regimens in patients undergoing neurotoxic oncologic therapies and patients under minimal conscious states. The prospective influences of auditory feedback proposed in these perspective articles are derived from the findings of both the review and research studies performed in this doctoral research work. In conclusion, this doctoral work demonstrates the intricate relationship between the auditory and proprioceptive modalities that could be utilized to develop efficient training and rehabilitative interventions. This research work for the first time developed a state of the art knowledge from the existing literature for the influence of auditory-motor training interventions. This novel work also demonstrates how self-generated auditory stimulations could be effectively used to facilitate proprioceptive perceptions i.e. an integral component of motor control and performance.