Introduction

When individuals want to share an idea verbally, they transform their thoughts into something physical (i.e., speech) that can be sent across space to the listener. Speech production is a fast moving, highly coordinated process involving the simultaneous use of hundreds of muscles, nerves, tendons, bones, and various other structures (Perkins and Kent,1986). These structures are organized into various subsystems including the respiratory system (breath support), the phonatory system (voice), and the articulatory system (speech sounds). These subsystems are highly interactive and have the potential to affect each other. This paper looksat the interactive nature of the speech subsystems and examines the common ground between voice therapy and stuttering therapy.

Voice disorders have a variety of causes, but for a significant number of people, the problem is in how they use the vocal mechanism. For these individuals, the main focus of therapy is on helping them learn a more normal use of the vocal mechanism and in many cases, resolving emotional or psychological issues related to their voice problems. Most stuttering therapy approaches also pay considerable attention to both physical and psychological aspects of the communication. Many approaches encourage relaxed voicing, focus on breath control, and easy voice onset. Some even make voice the centerpiece of treatment (Weiner, 1984).

Before discussing some possible relationships between voice and stuttering therapy, a brief overview of laryngeal structure and function provides a general understanding of the mechanism and how it works. The larynx, which is one of the main sound generators for speech, is located at the top of the trachea (wind pipe) and is suspended in the neck by muscles. The larynx consists mostly of cartilages, membranes, and muscles. In order to produce voice, air must be inhaled and trapped below the vocal folds. When the forces of exhalation become sufficient to blow the vocal folds apart, the folds separate and a sudden puff of air is released into the vocal tract (throat). The folds close again and the process is repeated very rapidly during voice production. In the average female, the vocal folds separate and close about 225 times per second during voicing.

Voice Therapy

This article concentrates on therapy strategies that are commonly used in treating vocal hyperfunction; a term used to describe the use of excessive muscle tension in the larynx. The problems that underlie vocal hyperfunction are similar to those underlying stuttering with a laryngealcomponent. While voice therapy involves considerable attention to phonation (voicing), voice clients often benefit from adjustment of additional subsystems of voice such as breathing and resonance.

Respiration (Speech Breathing)

The therapeutic goal for this area is to assure that the client uses a speech breathing strategy that is efficient and coordinates well with the laryngeal system. If speech breathing problems are identified, they are often related to the quantity of air inspired for speech (e.g., too little or too much) and/or the skill with which the client is able to coordinate laryngeal and respiratory muscle forces.

Lung volume issues

Speakers who breathe too deeply before speaking create an excessive amount of relaxation pressure inside the chest. Relaxation pressure is the force that causes air to be released from the lungs on exhalation. When relaxation pressure is greater than the pressure requirements for voice and speech, the individual must somehow deal with the excess pressure. Some people manage the pressure by using the larynx as a flow regulator or valve trying to hold back the excessive pressure (Morrison & Rammage, 1993). As a result, their speech is characterized by hard glottal attacks, excessive loudness, and a pressed quality. For individuals who stutter, this sort of breathing strategy could encourage laryngeal tension making it difficult to use a relaxed voice onset. Van Riper (1982) described how stutterers have greater success when speaking at lower lung volumes. He stated, A strong relationship exists between the amount of muscle activity at a closure site and the amount of air pressure behind it (p. 129).

Weismer (1985) described a desirable breathing technique. He explained that efficient speech breathing is accomplished when normal loudness is initiated in the area of 60 % of vital capacity and is terminated around 40% of vital capacity. In this situation, the speaker produces a reasonable amount of relaxation pressure to assist with phonation, and terminates the utterance before having to use a squeezing effort to support the voice later in the utterance. Avoiding these extremes will facilitate a relaxed larynx. Because most clients are not familiar with the concept of vital capacity, help must be provided for the client to recognize the upper and lower limits of this range. It is helpful to teach them to identify the sensations that are associated with the target lung volumes. Speech that is produced at a normal loudness is typically initiated at approximately 55-60 % of vital capacity (Kent, 1996; Perkins and Kent, 1986). This lung volume is slightly more than what a speaker would inhale for a quiet, resting breath. The client can simply be told to monitor the sensation of inhaling during a quiet breath, and to inhale only slightly more for speech at a normal conversational loudness level. When speech is initiated at this lung volume, there should be relative harmony between the amount of pressure below the vocal folds and that, which is required for voice and speech.

Coordinating the Respiratory and Laryngeal Systems

Aside from lung volume issues, certain voice clients seem to lack the ability to use the respiratory and laryngeal systems in a coordinated manner. Similar coordination problems have been reported as a characteristic of stuttering as well (Guitar, 1998). In people who stutter, behaviors range from late onset of voice (relative to the onset of airflow) to hard glottal attack, in which the vocal folds are firmly closed before the onset of airflow (Williams and Brutten, 1994; Weiner,1984). When a speaker uses a hard glottal attack to initiate the voice, he/she inspires air and then holds the breath before initiating the utterance. As mentioned earlier, this sabotages any effort to produce an utterance with a relaxed voice onset.

Relaxed voice onset, which is a key part of both voice and stuttering therapy, requires the speaker to coordinate vocal fold closure with the first outflow of air. This is a technique that Rammage (1996) calls the coordinated voice onset. The client should be instructed to inspire a normal volume of air and to initiate vocal fold closure at the very moment when inspiration has stopped and when expiration is about to begin. This is a rather narrow time window. The client takes in a breath immediately before beginning the utterance and the key is to avoid holding the breath as one prepares to speak. This technique is consistent with stuttering therapy approaches that encourage easy onset (Azrin & Nunn, 1974; Weiner, 1984) and fluency enhancing behaviors (Guitar, 1998).

Another related problem that sometimes occurs later in an utterance involves flawed strategies for maintaining subglottic pressure. During an utterance, relaxation pressure eventually becomes depleted and there is a need to further increase the role of the muscles of expiration in order to maintain sufficient subglottic pressure (Hixon, 1995). This is accomplished largely with muscles of the internal rib cage and abdomen. The flawed strategy occurs when speakers also increase the activity of laryngeal musculature right along with their increased expiratory effort. In effect, they fail to use the respiratory system selectively, while maintaining a normal amount of laryngeal muscle tension. For these patients, vocal quality becomes more strained later in their utterance. Therapeutically, it is often helpful to point this out to clients and to work on maintaining a desirable amount of laryngeal tension or openness in the throat while supporting the voice with the respiratory muscles. It seems logical that this avoidance of laryngeal tension later in the utterance could potentially benefit the individual who stutters.

Phonation

The goal for the phonation component is for the client to adopt appropriate laryngeal behaviors that will allow the larynx to respond optimally to normal respiratory/aerodynamic forces being applied by the respiratory system. For voice patients, therapeutic efforts in this area typically involve modifying voice onset behavior (discussed above) and reducing vocal fold closure forces throughout the utterance. Because voice onset is tied so closely to respiratory behavior, the discussion about voice onset was presented in the section above and will not be repeated here.

When laryngeal tension is excessive throughout the utterance, more air pressure is needed to cause the vocal folds to begin vibrating and they remain closed longer during each vibratory cycle. The resulting voice sounds strained or pressed. There are a number of structured therapy programs that are designed to reduce laryngeal tension. Programs such as Vocal Re-Education Therapy (Mueller, 1989) and Confidential Voice (Colton and Casper, 1996) use facilitating approaches such as breathy phonation to reduce tension. This approach may be quite helpful for the person who stutters, since it promotes overall relaxation of the larynx and continuity of airflow throughout the utterance.

Another common technique used in voice therapy to keep tension out of the larynx is called linking (Lessac, 1994). In linking, the speaker links the final consonant in one word to the initial part of the following word. For individuals with voice or stuttering concerns, the use of linking is a way to reduce the many opportunities to use hard glottal attacks that occur during connected speech. Reducing these opportunities may help to improve fluency. Ham (1986) stated, Stuttering seems to occur more frequently after a pause when voicing must be reinitiated (p. 340).

Hard glottal attack occurs mostly on words that begin with a vowel sound. When linking, the speaker maintains airflow from the final consonant to initiate a word beginning with a vowel. For example, in the phrase this old house, the airflow from the /s/ in this is sustained as the speaker transitions into the word old. The utterance would sound like thi sold house. In another example, the phrase stop it would be produced like sto pit. Linking appears to be similar to the legato speech used by Ham (1986) in stuttering therapy. From a teaching standpoint, it is not reasonable to ask the client to try to anticipate all situations where linking can be used. Instead, they are advised to simply think about keeping the air flowing. This does not mean they should talk beyond the normal breath cycle. Speakers must remain alert to the sensation of a depleting air supply and pause in an appropriate place for another breath.

While it seems logical that direct concentration on relaxing the larynx is helpful, it is frequently effective to use an approach where the clientıs attention is diverted away from the larynx and they focus on something else. One such approach is Resonant Voice therapy (Lessac, 1994; Verdolini-Marston et al., 1995). This therapy approach focuses on maximizing oral resonance, but it has been shown to be effective in resolving vocal nodules. Laryngeal imaging has revealed that the glottal closure pattern associated with resonant voice is ideal. There is just enough closure to produce a strong voice, but not so much that tissue damage occurs. The stronger voice is highly useful to the client and using the technique was reported to be better than other approaches such as those in which a breathy voice is produced. The resonant voice technique is discussed further in the following section relating to resonance.

Resonance

Sound that is created by the larynx is enhanced as it passes through and vibrates the resonating chambers of the vocal tract (i.e., the throat and mouth). A well-resonated voice sounds more pleasing and has more sound energy to help the voice project across space. For voice clients, the goal for resonance is to ensure that the client uses the voice-enhancing capabilities of the resonators to their best advantage. Weiner (1984) uses a focus on optimal oral resonance in stuttering clients as a means of improving vocal quality.

People who experience problems with the larynx sometimes focus excessively on the laryngeal area, thinking erroneously that increased laryngeal effort or concentration will somehow result in a better voice. This sort of compensatory behavior can not only increase laryngeal tension, but it may prevent someone from focusing on more desirable aspects of speaking such as the role of the resonating cavities. Resonant voice therapy was mentioned earlier because of its favorable effects on the laryngeal vibration pattern, but it has two other desirable effects. It helps divert attention away from the larynx, and it also results in a stronger, richer sounding voice. This approach involves using a mental focus on the alveolar ridge area (roof of the mouth just behind the upper teeth). The client is instructed to sustain certain sounds and monitor vibration on the alveolar ridge during phonation. Acoustically, these vibrations add to the overall strength of the voice. This approach may also be of value in stuttering therapy because of its capacity to divert attention away from the larynx while helping to produce a stronger voice without increasing laryngeal effort.

Other strategies can be implemented in order to improve resonance. Clients can be encouraged to release but not force the jaw open so that the acoustic energy can be freely radiated into space. To accomplish this, it is sometimes helpful to encourage patients to focus on the vowels in words and to welcome them as opportunities to open and relax the vocal tract during speech. Unlike consonants, the vowels are produced with a relatively open vocal tract that is free from significant constriction. In contrast, consonants are produced by impounding air behind a blockage (e.g., plosives such as p, b, t, d, k, g) or by forcing air through a tight constriction (e.g., fricatives such as f, v, s, z, th, sh, etc.). By having the client focus on enjoying the openness of the vowels in their speech, a more relaxed, open vocal tract may be achieved and resonance may be facilitated. A secondary, but desirable effect of doing this is that the rate of speech is reduced slightly. This may be of particular benefit to the person who stutters.

Summary

It should not be surprising that voice and stuttering therapy share some common ground. As this article points out, converting our thoughts into speech is a highly integrated process using a relatively fine balance of muscle and aerodynamic forces. Both voice and stuttering problems can arise when these forces come out of balance. Therapy for both types of communication problems includes the need to normalize breathing, phonation, articulation, and resonance.