Graduation Date

Fall 12-18-2015

Document Type


Degree Name

Doctor of Philosophy (PhD)


Environmental Health, Occupational Health, and Toxicology

First Advisor

Nicholas Stergiou

Second Advisor

Mukul Mukherjee

Third Advisor

Ka-Chun Siu


It has been shown that approximate one-third of US adults aged 40 years and older (69 million US citizens) have some type of vestibular problems. These declining abilities of the vestibular system affect quality of life. Difficulties in performing daily activities (dressing, bathing, getting in and out of the bed and etc.) have been highly correlated to loss of balance due to vestibular disorders. The exact number of people affected by vestibular disorders is still difficult to quantify. This might be because symptoms are difficult to describe and differences exist in the qualifying criteria within and across studies. Thus, it is crucial to develop a valid assessment. To measure how each sensory system contributes to postural control during walking, we developed a novel Locomotor Sensory Organization Test (LSOT).

Our results indicate that the contribution of visual input is significantly increased during locomotion, compared to standing in similar sensory conflict conditions. The increased visual gain in the LSOT conditions reflects the importance of visual input for the control of locomotion. In addition, if we investigated the postural control in walking in time series, the results showed visual input also had an effect but was not as prominent as the somatosensory input. Moreover, while applying Mastoid vibration (MV) on healthy young and older adults combined with LSOT assessment, we found that MV produced a significant increase in the amount of sway variability. Significant changes in the temporal structure of sway variability were only observed in the anterior-posterior direction in both age groups. However, the MV effect on the measure of the temporal structure of variability is opposite where MV produced an increasing effect in young adults. This is a very important finding as vestibular disorders has been difficult to diagnose lacking a systematic assessment leading to speculations that more than 1/3 of adults in the US that are 40 and older may experience vestibular problems that have never been diagnosed. Our experimental design and the results produced could guide a more reliable screening of vestibular system deterioration.

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Permission for Dissertation

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