Many animals communicate with each other through sounds. Creatures such as whales and birds have a large repertoire of noises and calls, some with specific meanings. But in human beings our vocal facility has enabled us to develop a complex language, capable of not only straightforward communication but also of expressing abstract ideas and being recorded as the written word.
Sound is produced by the voice box, or larynx, and is functional from the moment of birth. Essentially the larynx consists of two fibrous bands, the vocal cords, which are stretched, held together and forced to vibrate as air is pushed between them from the lungs. But the sounds from the larynx are only a small part of the complex serial process called speaking. Essentially this process falls into three phases. In order to say something we must first have something to say. That is, in our mind we select and sort words. This happens in the speech centre which is situated in the cerebral cortex, the surface layer of the main part of the brain. The centre is closely linked to other areas that are involved in reading, understanding speech, and hand movements. Because major nerve pathways cross to the other side of the body from the brain, a right-handed person has his or her dominant speech centre on the left side of the brain.
Once we have made up our mind what we want to say, the second stage involves the transmission of nerve messages to the face, neck and chest to innervate the complex and co-ordinated movements that produce speech. The chest muscles force air from the lungs and tiny muscles stretch the vocal cords to produce the basic noises of spoken words, chiefly vowel sounds. Thirdly, the modification of these sounds, which are surprisingly monotonous when recorded by a microphone placed near the vocal cords, is by movements of the pharynx, palate, tongue and lips. The jaws and teeth contribute to the nature of the articulated sounds, along with the nasal passages and the air-filled, resonant sinus cavities within the skull bones of the face. In this way sounds are amplified, modulated, shaped into words and achieve their person-specific timbre. The entire process is heavily dependent on psychological and muscular control which is not instinctive but has to be learned, chiefly during the first few years of life.
Types of speech disorder
Specialists on speech disorders such as logopaedists or doctors, classify disorders of speech into three main categories in line with the above three-part process. In dysphasia, the problem is with the formulation of speech or language in the brain. In dysphonia there is a problem with sound production. In dysarthria the difficulty lies in articulation – the formation of distinct sounds, syllables and words. This classification is a simple one, but determining the location of a speech disorder is a complicated and interdependent matter and many conditions that could cause it do not clearly fall into one single category.
The ability to formulate words or link together groups of words arises in the brain. So the cause of any deficiency in this skill must also be found in the brain. Its most extreme form, aphasia, is seen in the deaf-mute person. Those born completely deaf cannot hear speech and thus can never learn fully to imitate it. However, great advances in the techniques of helping congenitally deaf children have made the existence of this category of ‘deaf and dumb’ individuals increasingly a thing of the past.
Less commonly a child is born with an inability to appreciate the meaning of spoken words (congenital ‘word deafness’) even though his or her hearing is quite normal. Why this occurs is not understood. Lesser degrees of hearing loss in children may occur as a result of ‘glue-ear’, in which a sticky fluid caused by repeated infections of the eustachian tube corrects in the middle ear, or as a result of other types of middle-ear disease. This can lead to slow speech learning or incorrect pronunciation of words. Treatment of the underlying condition in such cases usually enables the child to catch up and learn speech at a normal pace. Aphasia and dysphasia may appear in adulthood as a result of conditions which affect or destroy the speech centres in the brain. Stroke, severe head injury or cerebral tumour may involve the speech centre or its connections and give rise to ‘word deafness’, with an inability to speak coherently. Some of those affected are able to read and write quite normally, but when trying to speak they can produce only jumbled collections of words but with otherwise normal articulation and speaking rhythm.
In its most common form dysphonia involves hoarseness of the voice, which is usually caused by laryngitis associated with a cold or sore throat, or by overuse of the voice. The voice’s change in quality is the result of swelling and thickening of the vocal cords, giving rise to alterations in their vibration patterns. Talking may also be painful. The problem usually subsides spontaneously as the cold or sore throat gets better. More long-term forms of hoarseness occur in those who misuse or over-use their voices, such as small boys, singers, sergeant-majors and auctioneers. In this case the hoarseness may be caused by the formation of small corn-like thickenings of the vocal cords (singer’s nodules); these often disappear after a period of vocal rest but if they are numerous and persistent they may occasionally require treatment by surgical removal.
Tumours of the vocal cords also cause hoarseness and may be benign (polyps, papillomas) or malignant. Benign tumours are generally easily removed during a minor operation. Cancers of the larynx most commonly develop in men aged 50 to 60, especially those who smoke cigarettes. Doctors always suspect hoarseness in such a person as being the result of cancer until definitely proven otherwise following a biopsy or other tests. It is fortunate that hoarseness is a very early symptom and the results of treatment, in the form of radiotherapy andor surgical removal of the larynx (laryngectomy), are excellent in terms of survival.
Laryngectomy presents a great challenge to the patient, the doctor and the speech therapist. Without vocal cords, the patient must develop a new way of producing sounds for modification into speech by the movements of the mouth. Most simply the sound is generated by a small electromechanical vibrator or ‘buzzer’ held against the side of the throat. Many patients, however, become proficient at producing a ‘pseudovoice’ by swallowing air into the upper part of the oesophagus (gullet), from where it is forced out in the form of a controlled belch which can be formed into intelligible speech. It is common practice for patients about to undergo laryngectomy, and who are understandably fearful, to be introduced to others who have had the operation and have learned to speak again.
Over the years many surgeons have attempted to construct or implant an artificial larynx following laryngectomy but the results are rarely satisfactory. Most methods involve making some form of connection between the trachea (windpipe) and upper oesophagus or pharynx, so that air from the lungs can be blown through a fold of skin or a plastic ‘squeaker’ to produce sound. But it is extremely difficult to prevent the leakage of swallowed food and drink back into the trachea, with resultant coughing and the risk of a chest infection.
Complete loss of voice, or aphonia, occurs rarely as a result of total paralysis of the larynx caused by disease of the nearby thyroid gland or (even more rarely) its removal. But a more common form of aphonia is caused by psychological factors. This condition may well cure itself when the period of stress or depression which may have initiated it has passed. A few such patients are very difficult to treat and need the combined services of an ENT (Ear, Nose and Throat) surgeon, speech therapist and psychiatrist.
Any structural, muscular or neurological (nervous) disorder which interferes with the co-ordinated movements of articulating words will give rise to dysarthria. For example, a child born with a cleft palate is unable to close off the nasal passages during speech; whereas a child with swollen adenoids or an adult with nasal polyps is completely unable to breathe through the nose. Interestingly, although opposite in nature (unblockable nose versus always blocked nose) these conditions all give rise to a similar ‘nasal’ quality to the speech. Structural problems like these are usually amenable to surgery, although the assistance of a speech therapist may be required to complete normal speech rehabilitation.
There are numerous neurological causes that may interfere with muscle control and therefore speech. Facial paralysis (Bell’s palsy), Parkinson’s disease, multiple sclerosis, cerebral palsy (’spasticity’) and brain damage following head injury are some of the more common causes. Many cases are permanent or progressive, and treatment of the speech defect requires the close co-operation of patient, neurologist and speech therapist. The patient is also instructed in methods of non-verbal communication such as the sign language used by deaf people, and counselling the relatives and friends of is provided for the sufferer.
Stammering, or stuttering (there is no clear distinction), is a dysarthric disorder for which no precise cause has been determined. It takes many forms but it usually involves an uncontrolled repetition of sounds, commonly consonants, at the beginning of a speech passage, or a sudden break or complete stop in the flow of words. No neurological abnormality seems to be involved although studies suggest that 40 per cent of cases may be accounted for by the existence of a hereditary tendency towards the disorder.
One of the fastest-advancing fields allied to medicine is speech therapy. Its practitioners can help those who were deemed untreatable only 20 or 30 years ago. Virtually anyone with a speech defect, from the congenially totally deaf child to the older patient who undergoes laryngectomy, from the light to the heavy stutterer to the pronounced lisper, can improve their speech with guidance.
Speech therapists use many and varied techniques to help their patients. One older system is the use of visual card cues which depict the shape of the lips and the position of the tongue, teeth and cheeks when making certain sounds, particularly consonants. Patients are also encouraged to use their fingertips to feel their throats, and the throats of the therapist and others, in order to detect the characteristic patterns of vibrations for each vowel sound, and also the pitch -high or low – and rhythm which give human speech its natural fluency.
Modern advances in microelectronics have also provided tools for the speech therapists and their patients. Microphones record speech and apparatus turn the vibrations into a visual pattern on a screen. The therapist shows the patient the visual pattern made by a ‘normal’ sound and instructs him or her to copy it. Small vibration-detectors held against the neck can also be used in this way for the treatment of stammering. Stammerers are taught how to impose a strong rhythm on their speech so that the regularity carries them through what would have been a break in the flow.
Using these various techniques, spoken sounds are broken down into building blocks called phonemes. The person masters these and then concentrates on combining them into words or phrases. As with other forms of rehabilitation (or habilitation) the aim is to maximize each individual’s potential. The treatment of stammering is difficult and often demands great skill on the part of the speech therapist within whose province the responsibility for treatment largely rests. Treatment is usually accompanied by a programme of psychotherapy. Psychiatric programmes alone, however, have failed to produce superior results in treatment, and for a time it was thought that psychopharmacological drugs such as tranquillizers would accelerate recovery, but these have proved even less successful. The optimum method of treatment, therefore, is one which combines help for the patient to better adjust to the problems of his or her life, with the development of a technique for controlling his or her symptoms and anxiety. Because this type of treatment is not easy to effect in the short term, the eventual outcome is largely dependent upon the patient’s motivation and perseverance. The investigation of one possible cause of stammering, that of inappropriate parental responses to developing speech, has led to the successful implementation of a programme of prevention in that area. The growing child passes through a stage when his or her speech is characterized by various ‘non-fluencies’, and hestitations, syllable repetition that is, laborious searching for the correct word. In some families, especially those in which there is a history of stammering, there may be a tendency for parents to chastise the child unnecessarily, or even to try to prevent him or her from making these non-fluencies. In some children this parental interference makes them associate normal non-fluencies with feelings of insecurity and fear which can lead to stammering, especially when the child feels pressurized. Studies have shown that highlighting the problem to families at risk has indeed helped to reduce the number of stammerers.