Speech science refers to the study of production, transmission and perception of

speech Speech is a human vocal communication using language. Each language uses Phonetics, phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if ...

. Speech science involves

anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...

, in particular the anatomy of the oro-facial region and

neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defin ...

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

, and

acoustics Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician ...

Speech production

The production of speech is a highly complex motor task that involves approximately 100 orofacial, laryngeal, pharyngeal, and

respiratory muscles The muscles of respiration are the muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during q ...

. Precise and expeditious timing of these muscles is essential for the production of temporally complex speech sounds, which are characterized by transitions as short as 10 ms between frequency bands and an average speaking rate of approximately 15 sounds per second. Speech production requires airflow from the lungs (

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

) to be phonated through the

vocal fold The human voice consists of sound made by a human being Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedality, bipedalism and exceptional cognitive skills due to a large and compl ...

s of the larynx (

phonation The term phonation has slightly different meanings depending on the subfield of phonetics. Among some phoneticians, ''phonation'' is the process by which the vocal folds produce certain sounds through quasi-periodic vibration. This is the defini ...

) and resonated in the vocal cavities shaped by the

jaw The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serv ...

soft palate The soft palate (also known as the velum, palatal velum, or muscular palate) is, in mammals, the soft tissue constituting the back of the roof of the mouth. The soft palate is part of the palate of the mouth; the other part is the hard palate. ...

lip The lips are the visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be ...

tongue The tongue is a muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper surfa ...

and other articulators ( articulation).

Respiration

Respiration is the physical process of gas exchange between an organism and its environment involving four steps (

ventilation Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Ventilator, a m ...

, distribution, perfusion and diffusion) and two processes (inspiration and expiration).

Respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

can be described as the mechanical process of air flowing into and out of the

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

s on the principle of

Boyle's law Boyle's law, also referred to as the Boyle–Mariotte law, or Mariotte's law (especially in France), is an experimental gas law that describes the relationship between pressure and volume of a confined gas. Boyle's law has been stated as: The ...

, stating that, as the volume of a container increases, the air pressure will decrease. This relatively negative pressure will cause air to enter the container until the pressure is equalized. During inspiration of air, the diaphragm contracts and the lungs expand drawn by

pleurae The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane overlying the lungs and the inside of the surrounding chest walls. The inner pleura, called the visceral pleura, covers the surface of each lung and dips be ...

through surface tension and negative pressure. When the lungs expand, air pressure becomes negative compared to atmospheric pressure and air will flow from the area of higher pressure to fill the lungs. Forced inspiration for speech uses accessory muscles to elevate the

rib cage The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels. The sternum, together known as the thoracic cage, is a semi- ...

and enlarge the

thoracic cavity The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...

in the vertical and lateral dimensions. During forced expiration for speech, muscles of the trunk and

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

reduce the size of the thoracic cavity by compressing the abdomen or pulling the rib cage down forcing air out of the lungs.

Phonation

Phonation is the production of a periodic sound wave by vibration of the

vocal folds In humans, vocal cords, also known as vocal folds or voice reeds, are folds of throat tissues that are key in creating sounds through vocalization. The size of vocal cords affects the pitch of voice. Open when breathing and vibrating for speech ...

. Airflow from the lungs, as well as laryngeal muscle contraction, causes movement of the vocal folds. It is the properties of tension and elasticity that allow the vocal folds to be stretched, bunched, brought together and separated. During prephonation, the vocal folds move from the abducted to adducted position. Subglottal pressure builds and air flow forces the folds apart, inferiorly to superiorly. If the volume of airflow is constant, the velocity of the flow will increase at the area of constriction and cause a decrease in pressure below once distributed. This negative pressure will pull the initially blow open folds back together again. The cycle repeats until the vocal folds are abducted to inhibit phonation or to take a breath.

Articulation

In a third process of speech production, articulation, mobile and immobile structures of the face (articulators) adjust the shape of the

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...

and nasal cavities (

vocal tract The vocal tract is the cavity in human bodies and in animals where the sound produced at the sound source (larynx in mammals; syrinx (biology), syrinx in birds) is filtered. In birds it consists of the Vertebrate trachea, trachea, the Syrinx (bio ...

) as the vocal fold vibration sound passes through producing varying resonant frequencies.

Central nervous control

The analysis of brain lesions and the correlation between lesion locations and behavioral deficits were the most important sources of knowledge about the cerebral mechanisms underlying speech production for many years. The seminal lesion studies of

Paul Broca Pierre Paul Broca (, also , , ; 28 June 1824 – 9 July 1880) was a French physician, anatomist and anthropologist. He is best known for his research on Broca's area, a region of the frontal lobe that is named after him. Broca's area is involve ...

indicated that the production of speech relies on the functional integrity of the left

inferior frontal gyrus The inferior frontal gyrus (IFG), (gyrus frontalis inferior), is the lowest positioned gyrus of the frontal gyri, of the frontal lobe, and is part of the prefrontal cortex. Its superior border is the inferior frontal sulcus (which divides it f ...

. More recently, the results of noninvasive neuroimaging techniques, such as functional magnetic resonance imaging (fMRI), provide growing evidence that complex human skills are not primarily located in highly specialized brain areas (e.g.,

Broca's area Broca's area, or the Broca area (, also , ), is a region in the frontal lobe of the dominant Cerebral hemisphere, hemisphere, usually the left, of the Human brain, brain with functions linked to speech production. Language processing in the brai ...

) but are organized in networks connecting several different areas of both hemispheres instead. Functional neuroimaging identified a complex neural network underlying speech production including cortical and subcortical areas, such as the

supplementary motor area The supplementary motor area (SMA) is a part of the motor cortex of primates that contributes to the control of movement. It is located on the midline surface of the hemisphere just in front of (anterior to) the primary motor cortex leg representa ...

cingulate Cingulata, part of the superorder Xenarthra, is an order of armored New World placental mammals. Dasypodids and chlamyphorids, the armadillos, are the only surviving families in the order. Two groups of cingulates much larger than extant arm ...

motor areas,

primary motor cortex The primary motor cortex (Brodmann area 4) is a brain region that in humans is located in the dorsal portion of the frontal lobe. It is the primary region of the motor system and works in association with other motor areas including premotor co ...

basal ganglia The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an extern ...

, and

cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...

Speech perception

Speech perception refers to the understanding of speech. The beginning of the process towards understanding speech is first hearing the message that is spoken. The

auditory system The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs (the ears) and the auditory parts of the sensory system. System overview The outer ear funnels sound vibrations to the eardrum, increasin ...

receives sound signals starting at the outer ear. They enter the pinna and continue into the external

auditory canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the pinna to the eardrum and is about in length and in diameter. Stru ...

(ear canal) and then to the

eardrum In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear The outer ear, external ear, or auris externa is the extern ...

. Once in the

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the ...

, which consists of the

malleus The malleus, or hammer, is a hammer-shaped small bone or ossicle of the middle ear. It connects with the incus, and is attached to the inner surface of the eardrum. The word is Latin for 'hammer' or 'mallet'. It transmits the sound vibrations fro ...

, the

incus The ''incus'' (plural incudes) or anvil is a bone in the middle ear. The anvil-shaped small bone is one of three ossicles in the middle ear. The ''incus'' receives vibrations from the ''malleus'', to which it is connected laterally, and transmit ...

, and the

stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the foo ...

; the sounds are changed into mechanical energy. After being converted into mechanical energy, the message reaches the oval window, which is the beginning of the

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...

. Once inside the inner ear, the message is transferred into hydraulic energy by going through the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...

, which is filled with fluid, and on to the

Organ of Corti The organ of Corti, or spiral organ, is the receptor organ for hearing and is located in the mammalian cochlea. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses' action potential. Transd ...

. This organ again helps the sound to be transferred into a neural impulse that stimulates the auditory pathway and reaches the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

. Sound is then processed in

Heschl's gyrus The transverse temporal gyri, also called Heschl's gyri () or Heschl's convolutions, are gyri found in the area of primary auditory cortex buried within the lateral sulcus of the human brain, occupying Brodmann areas 41 and 42. Transverse tempora ...

and associated with meaning in

Wernicke's area Wernicke's area (; ), also called Wernicke's speech area, is one of the two parts of the cerebral cortex that are linked to speech, the other being Broca's area. It is involved in the comprehension of written and spoken language, in contrast to B ...

. As for theories of speech perception, there are a motor and an auditory theory. The motor theory is based upon the premise that speech sounds are encoded in the acoustic signal rather than enciphered in it. The auditory theory puts greater emphasis on the sensory and filtering mechanisms of the listener and suggests that speech knowledge is a minor role that’s only used in hard perceptual conditions.

Transmission of speech

Speech is transmitted through

sound waves In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...

, which follow the basic principles of

. The source of all sound is vibration. For sound to exist, a source (something put into vibration) and a medium (something to transmit the vibrations) are necessary. Since sound waves are produced by a vibrating body, the vibrating object moves in one direction and compresses the air directly in front of it. As the vibrating object moves in the opposite direction, the pressure on the air is lessened so that an expansion, or rarefaction, of air molecules occurs. One compression and one rarefaction make up one

longitudinal wave Longitudinal waves are waves in which the vibration of the medium is parallel ("along") to the direction the wave travels and displacement of the medium is in the same (or opposite) direction of the wave propagation. Mechanical longitudinal waves ...

. The vibrating air molecules move back and forth parallel to the direction of motion of the wave, receiving energy from adjacent molecules nearer the source and passing the energy to adjacent molecules farther from the source. Sound waves have two general characteristics: A disturbance is in some identifiable medium in which energy is transmitted from place to place, but the medium does not travel between two places. Important basic characteristics of waves are wavelength, amplitude, period, and frequency.

Wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

is the length of the repeating wave shape.

Amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...

is the maximum displacement of the particles of the medium, which is determined by the energy of the wave. A period (measured in seconds) is the time for one wave to pass a given point.

Frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

of the wave is the number of waves passing a given point in a unit of time. Frequency is measured in hertz (hz); (Hz cycles per second) and is

perceived Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...

as pitch. Each complete vibration of a sound wave is called a cycle. Two other physical properties of sound are intensity and duration. Intensity is measured in decibels (dB) and is perceived as loudness. There are two types of tones:

pure tone Pure may refer to: Computing * A pure function * A pure virtual function * PureSystems, a family of computer systems introduced by IBM in 2012 * Pure Software, a company founded in 1991 by Reed Hastings to support the Purify tool * Pure-FTPd, ...

s and complex tones. The musical note produced by a

tuning fork A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs (tines) formed from a U-shaped bar of elastic metal (usually steel). It resonates at a specific constant pitch when set vibrating by striking it against ...

is called a pure tone because it consists of one tone sounding at just one frequency. Instruments get their specific sounds — their

timbre In music, timbre ( ), also known as tone color or tone quality (from psychoacoustics), is the perceived sound quality of a musical note, sound or musical tone, tone. Timbre distinguishes different types of sound production, such as choir voice ...

— because their sound comes from many different tones all sounding together at different frequencies. A single note played on a piano, for example, actually consists of several tones all sounding together at slightly different frequencies.