Speech repetition

Speech repetition is when one individual speaks the sounds they've heard another person pronounce or say. In other words, it is the saying by one individual of the spoken vocalizations made by another individual. Speech repetition requires person repeating the utterance to have the ability to map the sounds they hear from the other person's oral pronunciation to similar places and manners of articulation in their own vocal tract. Speech repetition is when one individual speaks the sounds they've heard another person pronounce or say. In other words, it is the saying by one individual of the spoken vocalizations made by another individual. Speech repetition requires person repeating the utterance to have the ability to map the sounds they hear from the other person's oral pronunciation to similar places and manners of articulation in their own vocal tract. Such speech input/output imitation often occurs independently of speech comprehension; such as in speech shadowing when a person automatically says words heard in earphones, and the pathological condition of echolalia in which people reflexively repeat overheard words. This links to speech repetition of words being separate in the brain to speech perception. Speech repetition occurs in the dorsal speech processing stream while speech perception occurs in the ventral speech processing stream. Repetitions are often incorporated unawares by this route into spontaneous novel sentences immediately or after delay following storage in phonological memory. In humans, the ability to map heard input vocalizations into motor output is highly developed due to this copying ability playing a critical role in a child's rapid expansion of their spoken vocabulary. In older children and adults it still remains important as it enables the continued learning of novel words and names and additional languages. Such repetition is also necessary for the propagation of language from generation to generation. It has also been suggested that the phonetic units out of which speech is made have been selected upon by the process of vocabulary expansion and vocabulary transmissions due to children preferentially copying words in terms of more easily imitated elementary units. Vocal imitation happens quickly: words can be repeated within 250-300 milliseconds both in normals (during speech shadowing) and during echolalia. The imitation of speech syllables possibly happens even quicker: people begin imitating the second phone in the syllable earlier than they can identify it (out of the set , and ). Indeed, '...simply executing a shift to upon detection of a second vowel in takes very little longer than does interpreting and executing it as a shadowed response'. Neurobiologically this suggests '...that the early phases of speech analysis yield information which is directly convertible to information required for speech production'. Vocal repetition can be done immediately as in speech shadowing and echolalia. It can also be done after the pattern of pronunciation is stored in short-term memory or long-term memory. It automatically uses both auditory and where available visual information about how a word is produced. The automatic nature of speech repetition was noted by Carl Wernicke, the late nineteenth century neurologist, who observed that 'The primary speech movements, enacted before the development of consciousness, are reflexive and mimicking in nature..'. Vocal imitiation arises in development before speech comprehension and also babbling: 18-week-old infants spontaneously copy vocal expressions provided the accompanying voice matches. Imitation of vowels has been found as young as 12 weeks. It is independent of native language, language skills, word comprehension and a speaker's intelligence. Many autistic and some mentally disabled people engage in the echolalia of overheard words (often their only vocal interaction with others) without understanding what they echo. Reflex uncontrolled echoing of others words and sentences occurs in roughly half of those with Gilles de la Tourette syndrome. The ability to repeat words without comprehension also occurs in mixed transcortical aphasia where it links to the sparing of the short-term phonological store. The ability to repeat and imitate speech sounds occurs separately to that of normal speech. Speech shadowing provides evidence of a 'privileged' input/output speech loop that is distinct to the other components of the speech system. Neurocognitive research likewise finds evidence of a direct (nonlexical) link between phonological analysis input and motor programming output. Speech sounds can be imitatively mapped into vocal articulations in spite of vocal tract anatomy differences in size and shape due to gender, age and individual anatomical variability. Such variability is extensive making input output mapping of speech more complex than a simple mapping of vocal track movements. The shape of the mouth varies widely: dentists recognize three basic shapes of palate: trapezoid, ovoid, and triagonal; six types of malocclusion between the two jaws; nine ways teeth relate to the dental arch and a wide range of maxillary and mandible deformities. Vocal sound can also vary due to dental injury and dental caries. Other factors that do not impede the sensory motor mapping needed for vocal imitation are gross oral deformations such as hare-lips, cleft palates or amputations of the tongue tip, pipe smoking, pencil biting and teeth clinching (such as in ventriloquism). Paranasal sinuses vary between individuals 20-fold in volume, and differ in the presence and the degree of their asymmetry. Vocal imitation occurs potentially in regard to a diverse range of phonetic units and types of vocalization. The world's languages use consonantal phones that differ in thirteen imitable vocal tract place of articulations (from the lips to the glottis). These phones can potentially be pronounced with eleven types of imitable manner of articulations (nasal stops to lateral clicks). Speech can be copied in regard to its social accent, intonation, pitch and individuality (as with entertainment impersonators). Speech can be articulated in ways which diverge considerably in speed, timbre, pitch, loudness and emotion. Speech further exists in different forms such as song, verse, scream and whisper. Intelligible speech can be produced with pragmatic intonation and in regional dialects and foreign accents. These aspects are readily copied: people asked to repeat speech-like words imitate not only phones but also accurately other pronunciation aspects such as fundamental frequency, schwa-syllable expression, voice spectra and lip kinematics, voice onset times, and regional accent.