Figure 1. A normal audiogram does not guarantee robust speech intelligibility in everyday listening conditions.
(A) Screening criteria for eligible audiology patient records from our hospital collected between 2000 and 2016. (B) Bilateral normal audiograms, defined as thresholds better than 20 dB HL (gray dashed line) were identified in 19% of the total patient population. Average audiograms from the left (blue) and right (red) ears are shown with individual data points in gray open circles. (C) Normalized age distribution of patients with bilateral normal audiograms shows a larger percentage of younger and middle-aged patients between 20–50 years of age. Black square indicates median age of 39 years. (D) Top five primary complaints that resulted in the visit to the clinic for these patients, including perceived hearing loss or decreased hearing presenting in 45% of these patients. (E) Schematic of a multi-talker digit recognition task. Subjects (N = 23) were familiarized with a target male speaker (red) producing four digits between 1 and 9 (excluding the bi-syllabic ‘7’), while two spatially co-localized distractors, one male and one female, with F0 frequencies above and below the target speaker simultaneously spoke four digits at varying signal-to-noise ratios (SNRs). (F) Accuracy decreased as a function of SNR at variable rates and to variable degrees. Correct trials required correctly reporting all four digits. (G) Variability in individual speech reception thresholds, defined as the SNR that produced a 70.7% success rate. Value at right represents sample mean ± SEM. (H) Auditory brainstem responses measured using ear canal tiptrodes yielded robust wave one amplitudes, a marker for auditory nerve integrity. Data reflect mean ± SEM. (I) Wave one values from individual subjects (left) and mean ± SEM of the sample (right). (J) No significant associations were observed between the ABR wave one amplitudes and speech reception threshold on the multi-talker digit task. r = Pearson’s correlation, and shaded area indicates 95% confidence intervals of the regression line (black) in Figures 1–4.