Study Sample − 50 participants were enrolled as part of clinical trial (ClinicalTrials.gov ID: NCT05848804) at a single site (Crossover Management, Wake Forest, NC) over 11 months. All Participants were 55 years of age or older, and fluent in English. Participants were excluded if they were unable to understand or unwilling to comply with testing instructions, reported a major psychiatric disorder such as bipolar disorder or if they had major medical problems such as cancer or epilepsy. Hearing tests were administered by a trained hearing instrumentation specialist after obtaining informed consent from each subject. Study procedures were approved by an independent Institutional Review Board (Advarra IRB Inc., Columbia, MD; www.advarra.com/) and was performed in accordance with relevant guidelines/regulations. Each participant was assigned (using the 4-block randomization method shown in Fig. 1) to one of two groups: the first group completed the audiogram first and then the dSHS, whereas the second group completed the dSHS first and then the audiogram. Equal numbers of participants were enrolled in each study arm.
Mobile Device Sound Output Calibration - The dSHS and cognitive assessment battery were conducted using an iPad Pro (11", 4th Generation, Wi-Fi, Apple, Inc., Cupertino, CA, USA). Sound levels produced by the iPad Pro were measured using a Type 2 calibrated SPL meter set to the International Electrotechnical Commission (IEC) and American National Standards Institute (ANSI) standards for electroacoustic devices (IEC 61672-1 class2, IEC651 Type2, ANSI14 Type2) placed 1 foot from the mobile device. Study participants were tested in a quiet environment testing center. Calibration is vital for comparison between the sound output levels of devices and for the threshold comparisons (PTA, SRT, and dSHS) made in this study to those of similarly calibrated devices used for audiometric assessment in the clinic.
Study Protocol - Pure tone average (PTA) thresholds were established at 500, 1000, and 2000 Hz tones. Speech recognition thresholds (SRT) were established during audiometric testing as the lowest levels at which pre-recorded speech presented at a consistent intensity could be recognized with at least 50% accuracy 15,16,22,23. The dSHS used nonsense words to avoid potential intrusion effects on subsequent cognitive testing. In the dSHS, a short, nonsense vowel-consonant-vowel (VCV) word was presented by the mobile device's external speakers (Fig. 2). Participants were asked to select from a list of 6 nonsense VCV words randomly selected from a constrained list, the one that best matched what they heard. If they did not hear or understand the word, participants were instructed to select “Didn’t Hear,” which was considered an incorrect response. The volume was increased incrementally by steps of 6.25% on the tablet following every incorrect response. The participant performed this task with several randomly selected VCV words until three consecutive correct responses were obtained. The DCR was then administered at the dSHS passing volume. If the dSHS reached 100% and an incorrect or “Didn’t Hear” selection was made, the DCR was administered at 100% volume. Hearing impairment was assessed in the context of cognitive performance in the DCR. Therefore, if participants normally wore hearing aids, they were instructed to wear them during the assessment to mimic their normal hearing conditions as closely as possible.
Statistical Analysis - Analysis was conducted in Matlab v9.3 (Mathworks, Inc., Natick, MA, USA). Pearson’s correlation coefficient was used to determine if there was a linear relationship between the average PTA and the volume level established by the hearing screener task. PTA thresholds were adapted to fit the nearest standards of hearing impairment established by the American Speech-Language and Hearing Association24 (ASHA). Normal hearing was classified as the reported average loudness of conversational speech25. Impaired hearing was classified using adapted thresholds for severe and profound hearing impairment 25. The maximum value of the audiogram response for the three frequencies was considered an outcome measure; however, PTA was used given its status as the standard clinical measure of hearing impairment.
One-way Analysis of Variance (ANOVA) was used to determine if there was a significant difference between Impaired and Unimpaired groups by the dSHS, where a clinical threshold of moderately impaired hearing24 was used to determine impaired hearing. Two different thresholds to identify the presence of hearing impairment, optimized for distinct contexts, were examined in this study. Each threshold was used to perform a binary classification analysis to determine the dSHS performance in classifying hearing impairment. The first threshold, 35dB, was based on the clinical standard for differentiating normal hearing from hearing impairment 26. The second threshold, 50dB, was intended to maximize the negative predictive value (NPV) in order to optimize the ruling-out greater than moderate hearing impairment. The area under the receiver operating characteristic (ROC) curve (AUC) was calculated to examine the discriminative ability of the dSHS between the Impaired and Unimpaired classes24.
To evaluate the performance of the dSHS in classifying hearing impairment, we used Classification accuracy (Acc) defined as the percentage of participants correctly classified as being impaired or not-impaired. The sensitivity (Sens) is defined as the percentage of participants classified correctly. Similarly, specificity (Spec) is defined as the percentage of impaired participants, correctly identified as such by the system. Positive and negative predictive values were also calculated to provide a measure of the predictive power of positive and negative (Impaired or Unimpaired) classifications. The positive predictive value (PPV) is defined as the proportion of participants, classified as impaired by the system, who were correctly classified. The negative predictive value (NPV) is the proportion of participants, classified as Unimpaired by the system, who are correctly classified. (The data that support the findings of this study are available from R.B. with the permission of Linus Health Inc.).