An Application for Screening Gradual-Onset Age-Related Hearing Loss

Objective: Less than 15% of adults in the USA over age 70 receive hearing screening; less than 20% of adults with hearing loss receive any form of treatment. Reasons vary, but affordability and accessibility are major barriers to intervention and treatment. This study provides data supporting a new adult hearing screening measure (NSRT®) that is self-administered, easy to use and focused on difficulties experienced in everyday speech communication. Methods: The NSRT® test materials are sentence-length utterances containing phonetic contrasts. The test requires respondents to determine whether sentences printed on a computer monitor are the same/different from sentences delivered as auditory stimuli through the computer sound card. The test is administered in quiet and +5 dB SNR background noise. Study participants were 120 adults aged 18 88 years. Results: Data obtained from the NSRT® testing experience are used to construct a pseudo audiogram. When the predicted hearing thresholds were compared with conventional, clinical puretone measures, the sensitivity and specificity of the NSRT screening measure were 95% and 87%, respectively; diagnostic accuracy was 91%. Conclusions: The NSRT® can identify individuals with hearing loss through a simple screening process grounded in standards set by the American Speech-LanguageHearing Association. The NSRT is suitable for administration in clinical and nonclinical settings.

able online and may be considered a low-tech approach to hearing screening.
High-tech approaches to hearing screening generally involve self-administered tests with stimuli presented under variable and uncontrolled listening conditions, and include screening with the use of land-line and cellular telephones, the internet, and hand-held consumer-electronic devices such as smartphones and tablet computers. Software applications have been developed for screening with the use of pure-tones, but results have proven problematic [3] [4] [5] [6] [7], and the calibration of devices and earphones remains a formidable challenge even for the most promising automated tests [8] [9]. However, progress is being made in addressing the calibration problem [10].
Since calibration problems make it difficult to deliver pure-tone tests over the internet and on mobile devices, stimulus materials consisting of speech in noise are used in some newer screening tests [11]- [19]. Although speech-in-noise screening provides a good measure of functional hearing capabilities, the correlation between these measures and pure-tone thresholds tends to be moderate [1] [18] [20]. Moreover, the outcome of some speech-in-noise screening measures differs qualitatively from pure-tone screening results. Instead of a dichotomous Pass-Fail outcome, the Speech Understanding in Noise screening test [13,14], for example, places respondents into one of three outcome categories: Pass, Hearing Check Advised, and Hearing Check Recommended.
The American Speech-Language-Hearing Association or ASHA [21] guidelines for hearing screening in adults stipulate that the stimulus materials consist of pure-tones at 1, 2 and 4 kHz presented at 25 dB HL. In order to pass the screening, the examinee must respond to all of the stimuli. Failure to respond at any one of the three frequencies results in a referral for a complete audiological evaluation. Since the stimuli are pure-tones presented at 25 dB HL, they must be delivered via a properly calibrated audiometer. Without a way to control the sound level and the user's selection of a transducer (earphones or speakers), it currently is not possible to develop a screening test which reflects the ASHA criteria and can be delivered over the internet. This is a formidable challenge facing the practice of tele-audiology and, in this regard, the ability to conduct hearing screening and simultaneously evaluate speech recognition ability may provide a useful alternative for testing conducted outside the clinical setting.
Using data obtained by the authors in earlier work [22], the present study investigates the degree to which an online adaptive test of speech recognition can serve as a proxy for pure-tone hearing screening methods. The investigation sought to quantify the accuracy of the NTID Speech Recognition Test (NSRT®) as a screening measure with regard to the American Speech-Language-Hearing Association (ASHA) criteria for hearing screening in adults [21]. Specifically, the present study sought to evaluate the effectiveness of the NSRT ® to separate test-takers who suffered from sensorineural hearing loss from those who were normally hearing, using the test criterion established by ASHA (i.e., the uniform screening level of 25 dB HL at pure-tone frequencies of 1, 2 and 4 kHz). Results of audiometric pure-tone testing in the clinical setting were compared to those predicted from online NSRT® testing. The outcome of each screening (i.e., traditional vs. NSRT®) was expressed as one of two possibilities: pass or refer a respondent for further evaluation.

Materials and Methods
Test Materials and Protocol: The NSRT ® is a computer-based adaptive test of speech recognition. Results of validity and reliability studies have been reported previously, as have various applications of the test [22] [23]. These results indicate high reliability coefficients for the NSRT ® and moderate correlations with pure-tone thresholds across the octave frequencies 0. Moreover, NSRT ® scores have been shown to provide insight into the phonetic errors that affect speech understanding in adults who suffer from sensorineural hearing loss. When combined with chronological age and self-report of hearing handicap in a multiple linear regression procedure, performance on the NSRT ® has been shown to be closely related to pure-tone thresholds for individuals having hearing losses < 55 dB HL. The close relationship between hearing thresholds and the combination of NSRT ® scores, age and self-report of hearing handicap enables the multiple regression algorithms to predict hearing thresholds in individuals having hearing sensitivity ranging from normal to moderate hearing loss.
The NSRT ® is composed of sentence-length utterances containing phonetic contrasts, primarily minimal pairs. The test protocol uses a paired comparison discrimination task in which a standard sentence is paired with two comparison sentences. Respondents must indicate if comparison sentences are the same or different from the standard sentence. Responses to the discrimination tasks are scored correct/incorrect. The NSRT ® is a computerized, adaptive test. It administers items utilizing an "up-down" method that selects items for presentation to respondents on the basis of their "information" value, a statistical concept. Like the stimuli used in adaptive psychophysical procedures, the stimuli used in adaptive testing are scaled along a continuum extending from low to high degrees of magnitude.
However, rather than representing a physical construct such as the intensity of a sound, the continuum in this instance represents a domain of human performance, speech recognition ability [24] [25].
The "up-down" method of item selection insures that the items administered to each respondent are selected from a narrow range of difficulty spanning their level of ability, which is itself constantly updated as items are administered during the testing process. The increase/decrease in item difficulty is associated with variation in the phonetic and acoustic properties of the utterances. Items continue to be administered until one of several test termination criteria has been met. These criteria include a predetermined time limit and number of items, as well as a pre-selected level of reliability. In addition, testing is terminated when the number of items within a specified range of difficulty has been exhausted.
For additional detail and background information regarding the item content and design of the NSRT ® application, the interested reader is referred to our earlier work [22] [23]. The NSRT ® application itself is accessible at https://apps.ntid.rit.edu/NSRT/. Pure-tone audiometric thresholds were obtained using standard audiometric procedures [26] at octave frequencies between 0.25 and 8 kHz. Air-bone gaps were ≤ 10 dB for all listeners. The signals were presented to participants' right/preferred ear through EAR-3A insert earphones at the NTID Audiology Clinic and the University at Buffalo, and TDH-50 supra-aural earphones at Syracuse University. Individuals with conductive hearing loss, as indicated by an air bone gap > 10 dB at any test frequency or failure to show a peak in the tympanogram between -200 and +200 daPa of ambient pressure in the test ear, were not included in the study. Table 1 summarizes the average hearing thresholds of all study participants computed across three different frequency ranges (i.e., lower, middle, and higher frequency ranges). Speech recognition threshold (SRT) data are also shown in the table. In this study, we focus on hearing screening at pure-tone frequencies of 1, 2 and 4 kHz, the criterion established by ASHA.

Participants and
In addition to pure-tone testing, all participants were administered the NSRT ® in both quiet and +5 dB SNR (signal-to-noise ratio) background noise (multi-talker babble). The NSRT ® was presented monaurally at 70 dB SPL or at participants' MCL if 70 dB SPL was less than 10 dB SPL re their PTA.
Data Analysis: In our earlier published work on the NSRT ® [22], we employ ordinary least squares (OLS) linear regression statistical procedures that combine the information obtained from an interactive testing experience in a man-

Results and Discussion
In the United States and Canada, the ASHA criteria for hearing screening are widely accepted as the gold standard. The ASHA standard for hearing screening in adults [21] is the criterion against which we evaluate the NSRT ® .
The effectiveness of a screening test is evaluated, in part, on the basis of its Measurements of sensitivity and specificity are commonly used to evaluate the efficacy of screening tests. When the clinically-obtained thresholds were compared to the online hearing screening test outcomes, the sensitivity of the NSRT ® was found to be 95%. The specificity of the NSRT ® was found to be 87%. The NSRT ® protocol was designed first and foremost to identify those individuals with age-related hearing loss who, through a simple screening procedure, could benefit from an intervention that might, otherwise, not have been realized owing to more restricted, costly audiological testing procedures. Hence, the sensitivity of the NSRT ® was primary in importance here. Overall diagnostic accuracy for hearing screening using the NSRT ® was 91%.  The percentages reported above the boxplot displays reflect the sizes of the subgroups of respondents, relative to the total sample of 120 participants. Figure   2 illustrates that the predicted PTA across the frequency range 1 to 4 kHz are most closely related to the PTA actually observed for individuals having hearing losses < 55 dB HL. The correspondence between observed and predicted PTA values is further reflected in a Pearson r = 0.90 (p < 0.01) across all 120 respondents.
Finally, hearing threshold data can also be represented by vectors. Vectors can be manipulated mathematically. In this study, we employ the cosine similarity The numerator of the equation for the cosine similarity index is the dot product (dp) of A and B. It holds information about the direction of the vectors. If dp AB > 0, A and B form an angle < 90 degrees. If dp AB = 0, A and B form an angle that is exactly 90 degrees, indicating orthogonality. If dp AB < 0, A and B form an angle > 90 degrees, not applicable here.
An angle of 0 degrees means that cos(θ) = 1, indicating that the vectors have identical directions. An angle of 90 degrees means that cos(θ) = 0, indicating that the vectors are perpendicular to one another.
Taking square roots, dp AA and dp BB hold length information. The formula for the computation of cos(θ) is a dot product/length product ratio, measuring the direction-length resemblance between two vectors representing corresponding data sets (i.e., observed vs. predicted hearing thresholds across the frequency range 1 to 4 kHz).

Conclusions
In this study, we evaluate the effectiveness of a hearing screening protocol that uses naturalistic speech-based stimulus materials to estimate hearing thresholds in individuals having hearing sensitivity ranging from normal to moderate hearing loss. The NSRT ® is a self-administered internet-based application accessible on home and office computers, as well as other wireless devices. The application is targeted on individuals who suffer from age-related, progressive, mild to moderate hearing loss. As such, it has the potential to reach tens of millions of individuals who might not otherwise avail themselves of audiological assessment procedures provided in a formal clinical setting.
A recent report by USA President Obama's Council of Advisors on Science and Technology (PCAST) indicates that hearing loss in an aging population is now a "substantial national problem," citing cost as the largest barrier to hearing technology access by individuals who could benefit from it, simultaneously advocating changes in FDA regulation that include disruptive improvements in both the assessment and treatment of hearing loss [27]. In the report PCAST indicates that, whereas the hearing healthcare needs of a growing population of Americans are not being met by existing market models, Americans might be "better served if non-surgical air-conduction devices intended to address bilateral, gradual-onset, mild-to-moderate age-related hearing loss were available over-the-counter (OTC)." The report goes on to state that "Simple hearing tests to aid consumers in purchasing such OTC hearing aids should also be available OTC, including on-line and in stores." Data presented in this study clearly indicate that the NSRT ® can serve as a proxy for pure-tone hearing screening methods. These data are especially impressive in light of the fact that differences on the order of +10 dB have been reported between thresholds obtained on hearing impaired persons with automated versus manual audiometry and test-retest reliabilities in standard audiometry [28] [29] [30] [31]. The NSRT® is most suitable for screening where the primary cause of hearing loss is age-related, the vast majority of cases. The application was developed using linear statistical methods. As such, the NSRT ® application focuses on detection of gradually-sloping or ski-slope hearing losses, by far the most common kind of hearing loss configuration. It was not intended to diagnose more complex kinds of hearing loss.
Beyond the obvious performance criteria that hearing screening tests must be sensitive and specific, demonstrated herein for the NSRT®, ASHA [21] guidelines for hearing screening tests require that such tests be: (1) easy to administer; (2) comfortable for the test taker; (3) short in duration; and (4) inexpensive. The NSRT® is self-administering and can be taken in the privacy of one's home, it is short in duration (5 -7 minutes) and freely available for use, and it provides respondents with informative reports of test performance immediately following a testing session. Because the application was developed for use primarily by persons aged 60+ years, who may face declines in cognitive and physical abilities associated with the use of electronic technologies, the NSRT® was designed in accordance with guidelines established by the National Institute on Aging and the National Library of Medicine in the USA [32]. The NSRT® application is accessible at https://apps.ntid.rit.edu/NSRT/.

Declarations
Funding: This research received NO specific grant from any funding agency, commercial or not-for-profit sectors.
Conflict of Interest: The authors declare that there is NO conflict of interest regarding the publication of this paper.