Veterans who have blast exposure and/or history of concussion (also referred to as mild traumatic brain injury, mTBI) often seek audiological assessment due to complaints of difficulty understanding speech in complex listening environments despite normal peripheral hearing sensitivity. The standard hearing test battery is not sensitive to these complaints, whereas auditory processing tests that use more complex stimuli may be more sensitive. In addition, it is possible that the complaints are related to non-auditory problems including visual and cognitive deficits, dizziness, tinnitus, and anxiety. However, some of the issues (e.g., visual deficits, anxiety) are outside audiologists? scope of practice. Therefore, the ideal approach is a multi-disciplinary, multi- modality assessment (e.g., Cacace & McFarland, 2005; 2009; Saunders & Echt, 2012). There is currently no evidence-based, universally-accepted test battery to assess this population, and limited systematic exploration of the auditory tests that should be included in such test battery. There is some evidence of abnormal performance on speech in noise, temporal processing, and binaural processing tasks in Veterans with blast exposure (Gallun, Diedesch et al., 2012; Saunders et al., 2015), which suggests that they should be included in the auditory portion of a multi-modality test battery. The goal of the current project is to examine additional tests of auditory response variability, listening effort, and working memory that might also be affected by blast exposure/mTBI (Aim 1). In addition, cortical auditory event-related potentials in response to speech-in-noise will be examined to determine this test is more sensitive to processing deficits than tests of pure tone or speech stimuli in quiet (Aim 2). Data for both aims will be obtained from all subjects in two groups of Veterans with and without history of blast exposure and/or mTBI to identify which measures have the best ability to separate the two groups. Participants age 18 to 55 years with normal hearing will be recruited. All participants will receive a standard hearing evaluation, as well as speech in noise, gap detection (temporal processing), and masking level difference (binaural processing). Subjects in the control group will be normal on all three tasks, whereas subjects in the blast exposure/mTBI group will be abnormal on at least one task. All subjects will complete questionnaires about tinnitus, dizziness, anxiety, and cognitive function in order to provide descriptive information about related disorders within each group.
Specific Aim 1 includes the Speech, Spatial, and Qualities of Hearing Scale (a measure of listening effort) and the Word Auditory Recognition and Recall Measure (WARRM, a measure of auditory working memory). Greater listening effort and poorer auditory working memory may contribute to complaints of difficulty understanding speech in noise. Moment-to-moment variability in processing sound (e.g., rapidly changing speech sounds) may also contribute to this complaint, and will be reflected as response variability in psychometric function (PF) slopes recovered from a tones in noise masking task. Performance on each test will be compared between the two participant groups using analysis of variance (ANOVA). It is hypothesized that listeners with history of blast exposure and/or mTBI will have shallower PF slopes, poorer working memory, and/or report greater listening effort. All or a subset of these tests would be included in the future test battery, depending on which ones yield significant differences between the groups.
In Specific Aim 2, the P300 will be elicited with speech (/da/ standard and /ga/ deviant) and non-speech stimuli (500 Hz standard and 1000 Hz deviant tones) in quiet and in multi-talker babble. ANOVAs will be used to compare amplitudes and latencies between the groups. It is hypothesized that P300 in participants with history of blast exposure and/or mTBI will have significantly smaller amplitudes and longer latencies quiet and in noise. Tests that are successful in separating the two groups will be included in the auditory portion of a multi-modality test battery that will be developed in the next step of this line of research.
Veterans with history of blast exposure and/or concussion (also referred to as mild traumatic brain injury, or mTBI) often have complaints of difficulty understanding speech in noise despite normal results on standard hearing tests. Such difficulties have an impact on their work and classroom performance, and quality of life in general. Identification of these auditory deficits requires complex listening tasks that are not included in standard hearing tests, and there is currently no evidence-based, universally-accepted test battery. In the current project, Veterans with and without history of blast exposure and/or mTBI will be given a battery of behavioral tests of response variability, listening effort, and auditory working memory, as well as non- behavioral tests of cortical correlates of speech-in-noise processing. The goal is to identify which measures have the best ability to separate the groups. These tests will be included in larger multi-modality, multi- disciplinary test battery.
