Assessing the Impact of mTBI on Multisensory Integration while Maneuvering on Foot

Rationale and Objective: Many studies have shown that military personnel with blast-related injuries or mild traumatic brain injury (mTBI) often suffer from significant impairments in their ability to process auditory and visual information. They also often experience substantial problems with vertigo, dizziness, and balance. Most research studies that have examined these problems with hearing, vision, and balance in detail have only looked at these individually. However, military personnel who desire to return to normal duty will experience many situations that will require them to use all of their senses at the same time. For instance, a military member who is patrolling on foot will always be scanning the battlefield for possible targets or threats, and, when a possibly interesting sound is heard, the first reaction will always be to turn and look at the source of the sound to determine its origin. Time-critical multisensory tasks of this type will require military personnel to combine information across all their senses in a way that cannot currently be evaluated in the clinic. The purpose of this study is to develop a sensitive test of multisensory integration that can be used to evaluate the functional performance of military personnel who have degraded sensory function due to blast-exposure and/or mTBI. This will be accomplished with a virtual reality system called CAREN, which combines a wide-angle video screen with a treadmill mounted on a moving platform and an array of loudspeakers mounted at different locations behind the screen. Subjects in the experiment will be asked to identify visual targets projected on the screen while ignoring a large number of visual distracters that look similar to the target. In some cases, the subjects will be aided in this visual search task by an auditory signal that originates from the location of the target. Their performance will be measured by the amount of time it takes them to locate the visual target, both in a condition where they are standing still and in a condition where they are walking on the treadmill. One aspect of the study is to determine whether blast-injured or mTBI personnel have particular difficulty combining information across senses. This will be determined by comparing performance in the blast-injured subjects to performance for normal subjects who have been degraded to the same level of visual and auditory performance by the addition of visual and auditory noise.

Applicability of Research: The most direct applicability of this research will be an assessment of whether mTBI and blast-injured military personnel have multisensory integration deficits that make their performance in complex tasks like dismounted patrolling worse than what would be predicted solely based on their individual measures of auditory, visual, and vestibular function. If no such deficit exists, then military care providers can be confident that military personnel who perform within normal acceptable limits on these individual sensory tests will be able to perform complex tasks that involve all three senses. However, if a deficit is detected, then military care providers will need to take this into account when making fitness-for-duty assessments for these personnel, and possibly implement rehabilitation strategies to address this problem. Currently, individuals who perform in the lower-normal range on many different sensory tests are still considered clinically normal and receive no rehabilitation.

Interim Outcomes: Very little information is available on multisensory integration in blast-exposed mTBI patients, so important interim information will be provided by this study, including information on the interaction between walking and audio and visual perception in normal and impaired patients, information on the impact of auditory perception on aurally aided visual search tasks, and information on the relationship between clinical sensory assessments and functional performance in complex multisensory tasks.

Expected Contributions to TBI Research: An improved understanding of multisensory integration in blast exposed patients; a sensitive objective measure of multisensory performance in mildly impaired patients with operational relevance to real-world military tasks.