The mechanics of speech

February 15, 2011

The mechanics of speech

Humans are complex beings. Every part of us is in some way interconnected. To communicate verbally with our peers, for instance, we use a system not only to produce sounds, but also to hear and understand them.

Basically, a sound is emitted by air being exhaled through a channel, modulated to produce the desired tone. This channel—the vocal tract—consists mainly of the larynx and mouth. The positioning of the different internal structures such as the vocal cords, tongue, teeth, palate and lips produces a characteristic sound referred to as a phoneme. Every language (English, French, etc.) has its own phonemes.

In the English language, this is how we modulate our vocal tract to pronounce vowels and conso-nants. Each phoneme we produce has an energy—frequency and temporal characteristics. This allows us to distinguish a long sound with a high level of energy and lower frequency, such as a vowel (a, i, o, u), or a very short sound with a lower level of energy and higher frequency, such as certain conso-nants (f, s, th).

Schematically, the letters, sounds and phonemes of our language fall into a frequency and energy zone. This zone, when transposed onto a graph used to interpret audiology results (audiogram), is shaped like a banana, hence the term speech banana (see figure 1).

The ability to communicate through speech cannot occur properly without a functioning control system: one’s hearing. The principle is a simple one: proper speech requires proper hearing. This is what is referred to as the phonological loop. The integrity of each decoding, transmission, judgment and emission structure is essential. For example, take someone who is completely deaf from birth. In the first few months of life, a child will produce babbling sounds. In a deaf child, these sounds will diminish and completely disappear. Such individuals are often wrongly referred to as “deaf-mute”. In fact, it’s not that they are unable to speak; they simply didn’t have the opportunity to learn how to modulate their vocal tract to produce sounds comprehensible to normally hearing people. They can learn alternative forms of communication such as sign language (ASL, LSQ), and specialized schools are also available to teach them how to communicate orally, such as the Montreal Oral School for the Deaf (MOSD).

The mechanics of speech

What about people whose deafness has developed during their lifetime?

The answer depends on the degree of deafness and the age at which it developed. The younger the age and greater the deafness, the more significant the impact on speech.

Consider someone whose hearing loss deprives them of some of the information contained in the speech banana (see figure 2). This person is therefore robbed of high-frequency content, i.e. the majority of consonants needed for word comprehension. As such, the individual may hear certain pho-nemes, but given the large amount of information missing, he or she will not be able to understand the meaning of a word, short of guessing. Some words in our language are very similar, such as bed-fed, time-dime, big-pig, parking-barking, hill-fill-sill, and we rely on high frequencies (consonants) to distinguish one from the other.

This impacts not only speech comprehension but pronunciation as well.

Keep in mind, we can’t repeat what we don’t hear.

In the long term, a patient with this level of deafness—especially if it developed at a young age—may no longer be able to properly pronounce sounds like “sh” or “ch.”

If you suspect problems with your hearing or even your pronunciation, don’t hesitate to consult your audioprosthetist at Lobe Santé auditive et communication’s multidisciplinary clinics for a hearing test. It’s the first step toward mitigating the impact of hearing loss on your word comprehension.