One of the first concepts an audiologist learns in his or her training is that of the degree of hearing loss. We all remember memorizing categories of hearing loss and learning to classify audiograms by degree, type, and configuration. The degree of hearing loss has quite reliably predicted a variety of communication outcomes for both children and adults; however, its limitations have always been clear. Clark reached back to 1929 in his discussion of the many attempts to develop a system to describe hearing loss (ASHA. 1981 Jul;23(7):493). While many of these systems have been lost to time (e.g., the Dundee Index, the Risberg-Martony overlay), they did attempt to generate a more fine-grained analysis of what Clark referred to as “the extent of the hearing handicap.” The same multifactorial problem of finding a way to describe an individual's hearing loss in a meaningful way continues to challenge us today. Although degree of hearing loss remains a key predictive variable, it does not as directly correlate with outcomes as it did in the past. A clear example of this is the case of individuals with severe-to-profound hearing loss who use cochlear implants. Despite having the most severe degrees of hearing loss, their functional hearing in everyday life with their implants may equal, or in some cases, surpass, that of individuals with a lesser degree of hearing loss. We see patients with severe hearing loss who function much better than what we might predict from their degree of hearing loss, and patients with mild hearing loss who surprisingly function poorly. Noting these, I believe that what we really need to be concerned with is not so much the degree of hearing loss as the degree of hearing access.
EVALUATING DISABILITY USING THE ICF MODEL
The World Health Organization's International Classification of Functioning, Disability and Health model, hereafter referred to as ICF, provides a useful framework for evaluating the impact of a disorder on a person's life (WHO, 2001 http://bit.ly/2mCHIGW). The components of this model include assessment of body functions and structures, activity and participation, and contextual factors (environmental and personal), all of which must be considered to understand the impact of a physical impairment on an individual's abilities to perform daily activities and participate fully at home, school, work, and in the community. The ICF model primarily focuses on functional health and emphasizes the importance of the interaction between an individual's health conditions or status and the surrounding contextual factors. For example, consider two school-aged children, Susie, who has mild hearing loss, and Jonathan, who has severe hearing loss. Table 1 illustrates how an individual's ability to participate in his/her own life (the gold standard of the ICF model) can be either directly or inversely correlated with measurements of body structure integrity (degree of hearing loss).
What is really evaluated using the ICF model when considering the idea of “degree of hearing access” is an individual's participation. To quote a former student, “I have a moderate-to-severe hearing loss, but on some days it feels moderate and some days it feels severe.” For this student, what is the factor(s) that determines whether her hearing loss on a particular day “feels” moderate or severe? She explained that it was as likely to be related to having an argument with her boyfriend as to being in a difficult acoustic environment. Using the concept of hearing access, in addition to the degree of hearing loss, will help patients better understand their hearing loss and hearing technology, as well as their expectations from their interactions with the world. Using the term “mild hearing loss” with a patient, for example, implies that the impact of hearing loss is only mild when in fact the acoustics in a patient's favorite restaurant are so poor that she has stopped taking her granddaughter out for a weekly lunch because her access to auditory information in that environment is severely impacted. For children, the degree of hearing access determines the degree of access to spoken language, the prerequisite to language acquisition. Determining the degree of hearing access requires the evaluation of the following four factors.
1. AUDITORY INTEGRITY
Auditory integrity relates to the characteristics of an individual's hearing loss and auditory system, including but not restricted to, the ability to detect pure tone stimuli. Our toolbox of assessments continues to expand to include more complex measures (e.g., speech discrimination, loudness perception, localization, etc.) to form a more comprehensive picture of auditory integrity. Daniel Ling often compared the pure tone audiogram with a shoreline, with residual hearing represented by the water (Ling. AG Bell, 1989). It is easy to see where the water starts, but how deep, cold, or murky the water was (i.e., to what extent residual hearing is clear and usable) remains a mystery. Audiologists need to take advantage of as many assessment tools as possible to find out what is under the water (so to speak) beyond pure tone audiograms and speech perception measures in quiet.
2. AMPLIFICATION INTEGRITY
Amplification integrity is the second variable for optimal access to communication. This goes without saying and it is in fact the only variable over which audiologists have much ability to change. There is really no need for discussion on the need for the fitting of appropriate amplification that meets the needs of each patient. However, it is worth highlighting that the presence of hearing aids, cochlear implants, bone-anchored hearing devices, or hearing assistance technology on a person's head does not mean that the technology is working. This reminder is particularly important for teachers and school staff who work with children who may not have the language, auditory, or self-advocacy skills to report hearing problems or issues with their hearing device(s). For adults, amplification devices that are sitting inside a drawer because of the patient's resistance, inadequate understanding of the device's use and maintenance, or other reasons have no chance to provide access to communication.
3. INDIVIDUAL FACTORS
This miscellaneous category necessarily encompasses various factors, ranging from age to cognitive ability to complex needs to self-advocacy, but it is an important category that patients have some ability to change. For example, Weinstein reminds us of the importance of self-report measures as an outcome measurement tool (Hearing Journal. 2015;68(11):26 http://bit.ly/2M77AWr). We should expand the notion of these tools as self-report measures and consider them to also be self-assessment measures. Self-assessment plays an important role in the development of metacognitive and problem-solving skills. Using self-report measures as counselling tools can help patients develop the ability to assess their own performance in different communicative situations, including their independent problem-solving skills during communication breakdowns (FEMS Microbiol Lett. 2017 Jun 15;364(11)).
This factor considers the physical listening environment as well as the speaker variables of the communication partner and the complexity of listening tasks. This is the most dynamic factor. The degree of hearing access can change instantly when a ventilation fan turns on during a work meeting or a teacher opens a window while a lawn mower is being operated just outside the classroom. In the ICF model, this category was conceptualized to be much broader than just the individual's physical space; it also refers to the individual's broader social context. Much of our work on overcoming difficult acoustic environments is focused on assistive devices, but audiologists also need to continue to advocate for universal design for hearing (What Works? Research into Practice, 2009 http://bit.ly/2JRDMeJ).
If the degree of hearing access encompasses many variables, how are we to evaluate it? We do have some measures of degree of hearing access that are perhaps not as widely used as they could be. Measures such as the speech intelligibility index (SSI) or various tests of speech understanding in noise provide a more comprehensive understanding of an individual's degree of hearing access than do pure tone thresholds (although the latter are still more predictive than actual measures of communication access in the real world). The Listening Age Formula from the Cottage School for the Deaf attempts to account for the factors that determine the amount of time that a child had access to auditory information in his or her life. There have been exciting new developments in the area of evaluating listening effort, providing further insight into the factors related to degree of hearing access (J Speech Lang Hear Res. 2011 Jun;54(3):944; Int J Audiol. 2018 Jun;57(6):457).
Although we have tools to evaluate each of these four factors, it seems unlikely that we can ever combine these into a reliable and valid quantitative measurement (what would be the unit of measurement?). However, using the concept of degree of hearing access—even in an informal descriptive way (e.g., excellent, good, fair)—may help patients anticipate and better manage communication breakdowns over the course of their day. The degree of hearing loss is a valid and reliable indicator of access to soft sounds; however, adding the concept of degree of hearing access to our clinical evaluation adds a useful dimension to better serve patients with hearing loss, their families, and the community.