Human speech is beautifully complex.

Speech is a stream of complex sounds made up of many different frequencies, or pitches (like keys on a piano). Due to the complex vibration of human vocal folds as well as the movements of many articulators on the mouth (tongue, lips, teeth), speech does not carry a single simple tone, but rather multiple tones organized into what is called a “harmonic spectrum”. The harmonic spectrum of speech contains both low pitched and high pitched tones.  The specific construction of this spectrum is what gives each speech sound its meaning, and allows them to be distinguished from other speech sounds. Most of the power of speech is contained in low frequency sounds, including vowels, and other voiced components such as m, d, b, g. However, the intelligibility of speech is carried in the high pitches, in consonants without voicing such as s, f, t, th, ph, ch, k. 

Communication complications of hearing loss

When a listener is suffering from hearing loss, they lose access to some portion of this spectrum, interfering with the intelligibility of the signal. The most common scenario is the individual with high frequency hearing loss, which occurs due to the natural resonance of the human ear canal as well as exposure to factors such as noise and normal genetics. This type of hearing loss is particularly insidious, because the normal or near-normal low frequency hearing can give the person a perception of not having a hearing loss. However, they are continually losing portions of the speech signal, needing repetitions, and misunderstanding things.  They hear a voice, but due to some consonants being inaudible,  they cannot make out the specific message, and words can become smeared. It is logical to say that background noise is an interference to speech intelligibility, as this is so even for normal hearing listeners. However, when an individual experiences high frequency hearing loss, they lose intelligibility of the speech signal due to the hearing loss, in addition to being bombarded with low frequency background noise which obscures the speech signal even further.  

Another major contributor to poor speech perception in individuals with hearing loss is the effect of sensory deprivation on the entire auditory system.  The ear is simply a sensory end organ, it is the brain which must understand and interpret the signal, and make sense out of it. This is an input dependent system, but the pathways involved in this system do not simply fall into disuse as a result of deprivation, rather they become reorganized and begin “doing” other things. When that input is reintroduced to the auditory system via hearing aids, the individual can become confused and overwhelmed.  The sudden influx of sounds that haven’t been heard in years can present a sensation of turning the lights on in the middle of the night.  An additional difficulty can be a total loss of function of nerve cells associated with certain pitch ranges  and cannot be stimulated with hearing aids.  This contributes to a distorted signal for the listener, no matter how loud we amplify.  However, after a time period of adjustment to these novel stimuli, sounds may become more recognizable and natural sounding even for an impaired auditory system with poor frequency resolution.

Success with hearing aids

It generally requires a great deal of motivation and emotional investment on behalf of the new hearing aid user to overcome this crucial time period of adjustment, but with consistent hearing aid use and clinician support, over time, the hearing aid user can adjust to a new way of listening. The bad news is that listening through a hearing aid will never sound as true-to-life as normal hearing. In order for a hearing aid fitting to be successful, it is imperative that the patient has appropriate expectations and understands limitations of hearing aid capabilities.

The good news is two-fold: 1.) The human auditory system is capable of adapting to just about any new situation, as long as the listener is willing to wear their hearing aids at least 10-15 hours a day, and 2.) New hearing aid technology offers a number of possible solutions to noise management and improving speech intelligibility. It is important for the new hearing aid user to understand that all individuals adjust differently to ther hearing aids.  It is not solely dependent on the severity of the hearing loss but also associated with personality type, motivation to hear better, and ability to adapt to new situations. 

An important point

The duration of the hearing loss plays a crucial role in the ease of this accomodation period. For this reason, hearing health practitioners are engaged in a public education effort to let our communities know that hearing aid users are more successful with hearing aids when they are fitted earlier in life and earlier in the progression of the hearing loss.  It may initially seem less beneficial than desired to fit a mild hearing loss, as they won’t notice much of a change with their new aids. However, a person can grow into their hearing aids. With proper follow up and management, the aids can be adjusted with changes in the hearing loss.  The individual who waits 20 years or more to seek help for their hearing loss will have a much more difficult time overcoming the nature of their hearing handicap.

Impaired speech intelligibility is unfortunately a reality of all hearing loss, due to natural patterns of human hearing degeneration. New hearing aid technology presents many possible options for assisting with these natural problems of hearing loss and typical listening challenges. Hearing professionals strongly encourage annual hearing evaluations beginning at age 45. Regular screenings will lead to an earlier diagnosis of a hearing loss. This can reduce the effects of auditory deprivation, increase speech intelligibility, and allow for the maximum possible benefit from hearing aids.