There is a resurgence of interest in understanding people with normal audiometric hearing thresholds but have difficulty hearing in noise. This interest stems from recent findings showing that synapses of auditory nerve fibers that respond to high-level sounds, not threshold sounds, can uncouple after aging or an insult like acoustic trauma (e.g., J Neurosci. 2009 Nov;29(45):14077); J Neurosci. 2013 Aug;33(34):13686). Called “cochlear synaptopathy,” this may cause “hidden hearing loss”–a condition wherein someone with normal hearing thresholds experiences an abnormal difficulty hearing in noise. Diagnostic tools to identify the etiology of hidden hearing loss are still being developed, and no treatment option is currently available. As such, in our recent study, we explored how patients with this condition could benefit from auditory training (AT), which is usually reserved for patients with moderate-to-profound hearing loss, and see their willingness to try this intervention (Otol Neurotol. 2018 Sep;39(8):950).
BENEFITS OF AUDITORY TRAINING
AT has been prescribed to patients with moderate-to-profound hearing loss to improve their ability to hear speech in quiet and in noise (J Speech Lang Hear Res. 2016 Aug;59(4):862; Glob J Health Sci. 2011 Apr;3(1):49; J Am Acad Audiol. 2005 Jun;16(7):494), and to reduce effort when listening to speech (Semin Hear. 2015 Nov; 36(4):263). Previous studies have shown that, in the laboratory, the ability to distinguish speech sounds can be improved when people with normal hearing practice AT. It is thus likely that a clinical population of patients with normal hearing thresholds could benefit from AT. Studies have shown multiple instances of physiological changes along the auditory pathway as a result of AT exercises among participants with normal hearing (e.g., Clin Neurophysiol. 2009 Jan;120(1):128; J Neurosci. 2008 May;28(19):4929).
Our study determined the prevalence of patients with normal thresholds but have difficulty listening in background noise and the likelihood that they would volunteer for AT as a treatment option for their complaints. Ultimately, the goal is to use objective measurements to quantify the benefits a person with hidden hearing loss can receive from AT.
The questionnaire-based study was conducted via phone interviews. The Adult Audiology Clinic in the department of otolaryngology at the Washington University School of Medicine in St. Louis provided a database of 11,938 patients who received a hearing examination over a period of approximately three and a half years. We contacted 2,299 patients with normal pure tone averages, of which 474 completed the phone interviews. Of these, only 135 participants (average age = 46.9 years, SD = 13.4) had bilateral hearing thresholds <25 dB HL at all octave frequencies up to 8 kHz, and we focused on these participants to avoid potentially confounding the results with those who have high-frequency hearing loss. None had air-bone gaps.
The 14-item questionnaire was developed to address two goals: (1) to estimate the prevalence of the problem within this population and (2) determine if AT would be an acceptable treatment option. To address the first goal, most questions focused on differentiating participants with normal hearing and experience a typical level of difficulty when listening in noise from participants who have disproportionate difficulty when listening in noise. For example, the participants were asked, “How often do you find it difficult to follow a conversation in background noise?” For the following questions, a five-point Likert scale was used:
- “Which statement best describes your hearing when there is no background noise?”
- “Which statement best describes your hearing when in the presence of background noise?”
A nominal scale was assigned to these responses: “Excellent” (0), “Good” (1), “A Little Trouble” (2), “Moderate Hearing Trouble” (3), “A Lot of Hearing trouble” (4), and “Deaf” (5). The objective was to gauge the difference between the parallel questions and estimate the participants’ level of difficulty when listening in noise. The histograms in Figure 1 show some study results, with the distributions of the participants’ response types on the primary axis.
To address the second goal, the participants were asked: “If there was a free auditory training program that might improve your ability to hear in noise, would you be willing to use the program?” The shaded portion of each bar in Figure 1 indicates the proportion of the 90 participants who responded positively (“Don't Know” or “Yes”) to the use of AT. Those who responded positively were asked two follow-up questions about their time commitment to the training: How often would you be willing to participate in half-hour sessions to complete the training (1) in your home or (2) in the doctor's office/clinic/office? Figure 2 shows the distribution of the participants’ location preferences.
RESULTS AND DISCUSSION
Across all relevant questions in the survey, approximately six to seven percent of participants said that they “Always” have difficulty hearing speech in noisy conditions (Fig. 1, far left bars). By noting only the most extreme answers to each relevant question, we made a conservative estimate of the prevalence of people with normal audiometric thresholds who reported difficulty hearing in noise. Notably, however, if the criteria were expanded to include those who “Usually” have trouble hearing in noise, the prevalence estimate climbs to 22 percent.
Approximately 67 percent of the sample responded “Don't Know” or “Yes” if they would be willing to volunteer for AT. The follow-up questions indicated that the amount of time they were willing to commit to AT was dependent on the location of the training. A once-a-week schedule was overwhelmingly preferred for in-office training. However, participants were willing to undergo more frequent training if it were conducted at home. The bi-modal distribution measuring in-home AT frequency showed that a relatively large number of participants would train every day if it was offered at home, suggesting that there is a subset of this population that is highly motivated to address their hearing difficulties in noise.
This investigation is a necessary first step in determining the effectiveness of and interest in AT within this patient population, as well as the criteria under which these patients would be willing to train. As we further refine our ability to identify this unique and underserved population, we see AT as a primary treatment option or perhaps a supplement if drug delivery to the inner ear is developed for hidden hearing loss.
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