Speech repetition occurs when individuals speak the sounds that they have 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 the person repeating the utterance to have the ability to map the sounds that 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 in which people automatically say words heard in earphones, and the pathological condition of echolalia in which people reflexively repeat overheard words. That links to speech repetition of words being separate in the brain to speech perception. Speech repetition occurs in the dorsal speech processing stream, and speech perception occurs in the ventral speech processing stream. Repetitions are often incorporated unawares by that route into spontaneous novel sentences immediately or after delay after the storage in phonological memory.
In humans, the ability to map heard input vocalizations into motor output is highly developed because of the copying ability playing a critical role in children's rapid expansion of their spoken vocabulary. In older children and adults, that ability remains important, as it enables the continued learning of novel words and names and additional languages. That 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 because children prefer to copy 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 more quickly: people begin imitating the second phone in the syllable [ao] earlier than they can identify it (out of the set [ao], [aæ] and [ai]). Indeed, "...simply executing a shift to [o] upon detection of a second vowel in [ao] 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..".
Independent of speech
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.
Diverse linguistic vocalizations
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.
In 1874 Carl Wernicke proposed that the ability to imitate speech plays a key role in language acquisition. This is now a widely researched issue in child development. A study of 17,000 one and two word utterances made by six children between 18 months to 25 months found that, depending upon the particular infant, between 5% and 45% of their words might be mimicked. These figures are minima since they concern only immediately heard words. Many words that may seem spontaneous are in fact delayed imitations heard days or weeks previously. At 13 months children who imitate new words (but not ones they already know) show a greater increase in noun vocabulary at four months and non noun vocabulary at eight months. A major predictor of vocabulary increase in both 20 months, 24 months, and older children between 4 and 8 years is their skill in repeating nonword phone sequences (a measure of mimicry and storage). This is also the case with children with Down's syndrome . The effect is larger than even age: in a study of 222 two-year-old children that had spoken vocabularies ranging between 3–601 words the ability to repeat nonwords accounted for 24% of the variance compared to 15% for age and 6% for gender (girls better than boys).
Nonvocabulary expansion uses of imitation
Imitation provides the basis for making longer sentences than children could otherwise spontaneously make on their own. Children analyze the linguistic rules, pronunciation patterns, and conversational pragmatics of speech by making monologues (often in crib talk) in which they repeat and manipulate in word play phrases and sentences previously overheard. Many proto-conversations involve children (and parents) repeating what each other has said in order to sustain social and linguistic interaction. It has been suggested that the conversion of speech sound into motor responses helps aid the vocal "alignment of interactions" by "coordinating the rhythm and melody of their speech". Repetition enables immigrant monolingual children to learn a second language by allowing them to take part in 'conversations'. Imitation related processes aids the storage of overheard words by putting them into speech based short- and long-term memory.
The ability to repeat nonwords predicts the ability to learn second-language vocabulary. A study found that adult polyglots performed better in short-term memory tasks such as repeating nonword vocalizations compared to nonpolyglots though both are otherwise similar in general intelligence, visuo-spatial short-term memory and paired-associate learning ability. Language delay in contrast links to impairments in vocal imitation.
Speech repetition and phones
Electrical brain stimulation research upon the human brain finds that 81% of areas that show disruption of phone identification are also those in which the imitating of oral movements is disrupted and vice versa; Brain injuries in the speech areas show a 0.9 correlation between those causing impairments to the copying of oral movements and those impairing phone production and perception.
Spoken words are sequences of motor movements organized around vocal tract gesture motor targets. Vocalization due to this is copied in terms of the motor goals that organize it rather than the exact movements with which it is produced. These vocal motor goals are auditory. According to James Abbs 'For speech motor actions, the individual articulatory movements would not appear to be controlled with regard to three- dimensional spatial targets, but rather with regard to their contribution to complex vocal tract goals such as resonance properties (e.g., shape, degree of constriction) and or aerodynamically significant variables'. Speech sounds also have duplicable higher-order characteristics such as rates and shape of modulations and rates and shape of frequency shifts. Such complex auditory goals (which often link—though not always—to internal vocal gestures) are detectable from the speech sound which they create.
Dorsal speech processing stream function
Two cortical processing streams exist: a ventral one which maps sound onto meaning, and a dorsal one, that maps sound onto motor representations. The dorsal stream projects from the posterior Sylvian fissure at the temporoparietal junction, onto frontal motor areas, and is not normally involved in speech perception. Carl Wernicke identified a pathway between the left posterior superior temporal sulcus (a cerebral cortex region sometimes called the Wernicke's area) as a centre of the sound "images" of speech and its syllables that connected through the arcuate fasciculus with part of the inferior frontal gyrus (sometimes called the Broca's area) responsible for their articulation. This pathway is now broadly identified as the dorsal speech pathway, one of the two pathways (together with the ventral pathway) that process speech. The posterior superior temporal gyrus is specialized for the transient representation of the phonetic sequences used for vocal repetition. Part of the auditory cortex also can represent aspects of speech such as its consonantal features.
Mirror neurons have been identified that both process the perception and production of motor movements. This is done not in terms of their exact motor performance but an inference of the intended motor goals with which it is organized. Mirror neurons that both perceive and produce the motor movements of speech have been identified. Speech is mirrored constantly into its articulations since speakers cannot know in advance that a word is unfamiliar and in need of repetition—which is only learnt after the opportunity to map it into articulations has gone. Thus, speakers if they are to incorporate unfamiliar words into their spoken vocabulary must by default map all spoken input.
Words in sign languages, unlike those in spoken ones, are made not of sequential units but of spatial configurations of subword unit arrangements, the spatial analogue of the sonic-chronological morphemes of spoken language. These words, like spoken ones, are learnt by imitation. Indeed, rare cases of compulsive sign-language echolalia exist in otherwise language-deficient deaf autistic individuals born into signing families. At least some cortical areas neurobiologically active during both sign and vocal speech, such as the auditory cortex, are associated with the act of imitation.
Birds learn their songs from those made by other birds. In several examples, birds show highly developed repetition abilities: the Sri Lankan Greater racket-tailed drongo (Dicrurus paradiseus) copies the calls of predators and the alarm signals of other birds Albert's lyrebird (Menura alberti) can accurately imitate the satin bowerbird (Ptilonorhynchus violaceus),
Research upon avian vocal motor neurons finds that they perceive their song as a series of articulatory gestures as in humans. Birds that can imitate humans, such as the Indian hill myna (Gracula religiosa), imitate human speech by mimicking the various speech formants, created by changing the shape of the human vocal tract, with different vibration frequencies of its internal tympaniform membrane. Indian hill mynahs also imitate such phonetic characteristics as voicing, fundamental frequencies, formant transitions, nasalization, and timing, through their vocal movements are made in a different way from those of the human vocal apparatus.
- Bottlenose dolphins can show spontaneous vocal mimicry of computer-generated whistles.
- Killer whales can mimic the barks of California sea lions.
- Harbor seals can mimic in a speech-like manner one or more English words and phrases
- Elephants can imitate trunk sounds.
- Lesser spear-nosed bat can learn their call structure from artificial playback.
- An orangutan has spontaneously copied the whistles of humans.
Apes taught language show an ability to imitate language signs with chimpanzees such as Washoe who was able to learn with his arms a vocabulary of 250 American Sign Language gestures. However, such human trained apes show no ability to imitate human speech vocalizations.
- Alan Baddeley
- Auditory processing disorder
- Baddeley's model of working memory
- Conduction aphasia
- Developmental verbal dyspraxia
- Echoic memory
- Language development
- Language acquisition
- Language-based learning disability
- Mirror neurons
- Mirroring (psychology)
- Motor cognition
- Motor theory of speech perception
- Origin of language
- Passive speakers
- Phonological development
- Second-language acquisition
- Short-term memory
- Speech perception
- Thematic coherence
- Transcortical motor aphasia
- Transcortical sensory aphasia
- Vocabulary growth
- Vocal learning
- Indefrey, P.; Levelt, W. J. M. (2004). "The spatial and temporal signatures of word production components". Cognition. 92 (1–2): 101–144. CiteSeerX 10.1.1.475.251. doi:10.1016/j.cognition.2002.06.001. PMID 15037128. S2CID 12662702.
- Marslen-Wilson, W. (1973). "Linguistic structure and speech shadowing at very short latencies". Nature. 244 (5417): 522–523. Bibcode:1973Natur.244..522M. doi:10.1038/244522a0. PMID 4621131. S2CID 4220775.
- Porter Jr, R. J.; Lubker, J. F. (1980). "Rapid reproduction of vowel-vowel sequences: Evidence for a fast and direct acoustic-motoric linkage in speech". Journal of Speech and Hearing Research. 23 (3): 593–602. doi:10.1044/jshr.2303.593. PMID 7421161.
- Gentilucci, M.; Cattaneo, L. (2005). "Automatic audiovisual integration in speech perception". Experimental Brain Research. 167 (1): 66–75. doi:10.1007/s00221-005-0008-z. PMID 16034571. S2CID 20166301.
- "Acute hepatitis B virus infection in children and teachers, England and Wales 1985-90". CDR (London, England : Weekly). 1 (17): 75–76. 1991. PMID 1669805.
- Wernicke K. The aphasia symptom-complex. 1874. Breslau, Cohn and Weigert. Translated in: Eling P, editor. Reader in the history of aphasia. Vol. 4. Amsterdam: John Benjamins; 1994. p. 69–89. ISBN 978-90-272-1893-3
- Kuhl, P. K.; Meltzoff, A. N. (1982). "The bimodal perception of speech in infancy". Science. 218 (4577): 1138–1141. Bibcode:1982Sci...218.1138K. doi:10.1126/science.7146899. PMID 7146899.
- Kuhl, P. K.; Meltzoff, A. N. (1996). "Infant vocalizations in response to speech: Vocal imitation and developmental change". The Journal of the Acoustical Society of America. 100 (4 Pt 1): 2425–2438. Bibcode:1996ASAJ..100.2425K. doi:10.1121/1.417951. PMC 3651031. PMID 8865648.
- Roberts, J. M. (1989). "Echolalia and comprehension in autistic children". Journal of Autism and Developmental Disorders. 19 (2): 271–281. doi:10.1007/BF02211846. PMID 2745392. S2CID 6925526.
- Schneider, DE (1938). "The clinical syndromes of echolalia, echopraxia, grasping and sucking". Journal of Nervous and Mental Disease. 88: 18–35, 200–216. doi:10.1097/00005053-193807000-00003. S2CID 143703500.
- Schuler, A. L. (1979). "Echolalia: Issues and clinical applications". The Journal of Speech and Hearing Disorders. 44 (4): 411–34. doi:10.1044/jshd.4404.411. PMID 390245.
- Stengel, E. (1947). "A Clinical and Psychological Study of Echo-Reactions". The British Journal of Psychiatry. 93 (392): 598–612. doi:10.1192/bjp.93.392.598. PMID 20273402.
- Lees, A. J.; Robertson, M.; Trimble, M. R.; Murray, N. M. (1984). "A clinical study of Gilles de la Tourette syndrome in the United Kingdom". Journal of Neurology, Neurosurgery, and Psychiatry. 47 (1): 1–8. doi:10.1136/jnnp.47.1.1. PMC 1027633. PMID 6582230.
- Trojano, L.; Fragassi, N. A.; Postiglione, A.; Grossi, D. (1988). "Mixed transcortical aphasia. On relative sparing of phonological short-term store in a case". Neuropsychologia. 26 (4): 633–638. doi:10.1016/0028-3932(88)90120-0. PMID 2457182. S2CID 35115074.
- McLeod P. Posner MI. (1984). Privileged loops from percept to act. In H. Bouma D. Bouwhuis, (Eds), Attention and performance X (pp. 55-66). Hillsdale, NJ, Erlbaum. ISBN 978-0-86377-005-0
- Coslett, H. B.; Roeltgen, D. P.; Gonzalez Rothi, L.; Heilman, K. M. (1987). "Transcortical sensory aphasia: Evidence for subtypes". Brain and Language. 32 (2): 362–378. doi:10.1016/0093-934X(87)90133-7. PMID 3690258. S2CID 6079313.
- McCarthy, R.; Warrington, E. K. (1984). "A two-route model of speech production. Evidence from aphasia". Brain : A Journal of Neurology. 107 (2): 463–485. doi:10.1093/brain/107.2.463. PMID 6722512.
- McCarthy, R. A.; Warrington, E. K. (2001). "Repeating Without Semantics: Surface Dysphasia?". Neurocase. 7 (1): 77–87. doi:10.1093/neucas/7.1.77. PMID 11239078.
- Bloomer HH. (1971). Speech defects associated with dental malocclusions and related abnormalities. In L. E. (Eds), Handbook of speech pathology and audiology (pp. 715-766), New York, Appleton Century. ISBN 978-0-13-381764-5
- Williams RJ. (1967). You are extra-ordinary. New York, Random House. pp. 26-27. OCLC 156187572
- Vocal traits also vary moreover when people get upper respiratory tract infections as the shape and size of sinus cavities is further changed with the swelling of mucous membranes.
- Kappes, J.; Baumgaertner, A.; Peschke, C.; Ziegler, W. (2009). "Unintended imitation in nonword repetition". Brain and Language. 111 (3): 140–151. doi:10.1016/j.bandl.2009.08.008. PMID 19811813. S2CID 2113790.
- Gentilucci, M; Bernardis, P (2007). "Imitation during phoneme production". Neuropsychologia. 45 (3): 608–15. doi:10.1016/j.neuropsychologia.2006.04.004. PMID 16698051. S2CID 40687020.
- Shockley, K.; Sabadini, L.; Fowler, C. A. (2004). "Imitation in shadowing words". Perception & Psychophysics. 66 (3): 422–429. doi:10.3758/BF03194890. PMID 15283067.
- Delvaux, V; Soquet, A (2007). "The influence of ambient speech on adult speech productions through unintentional imitation". Phonetica. 64 (2–3): 145–73. doi:10.1159/000107914. PMID 17914281. S2CID 22042824.
- Wernicke K. (1874). The aphasia symptom-complex. Breslau, Cohn and Weigert. Translated in: Eling P, editor. (1994). p. 69–89.Reader in the history of aphasia. Vol. 4. Amsterdam: John Benjamins: "The major tasks of the child in speech acquisition is mimicry of the spoken word". p76
- Bloom, L.; Hood, L.; Lightbown, P. (1974). "Imitation in language development: If, when, and why". Cognitive Psychology. 6 (3): 380–420. doi:10.1016/0010-0285(74)90018-8.
- Miller GA. (1977). Spontaneous apprentices: Children and language. New York, Seabury Press. ISBN 978-0-8164-9330-2
- Masur, EF (1995). "Infants' early verbal imitation and their later lexical development". Merrill-Palmer Quarterly. 41: 286–306. OCLC 89395784.
- Gathercole, SE. Baddeley AD. (1989). "Evaluation of the role of phonological STM in the development of vocabulary in children, A longitudinal study". Journal of Memory and Language. 28 (2): 200–213. doi:10.1016/0749-596x(89)90044-2.
- Gathercole, S. E. (2006). "Nonword repetition and word learning: The nature of the relationship". Applied Psycholinguistics. 27 (4): 513–543. doi:10.1017/S0142716406060383. S2CID 145633911. PDF Archived 2011-06-05 at the Wayback Machine
- Hoff, E; Core, C; Bridges, K (2008). "Non-word repetition assesses phonological memory and is related to vocabulary development in 20- to 24-month-olds". Journal of Child Language. 35 (4): 903–16. doi:10.1017/S0305000908008751. PMID 18838017. S2CID 18566002.
- Stokes, S. F.; Klee, T (2009). "Factors that influence vocabulary development in two-year-old children". Journal of Child Psychology and Psychiatry. 50 (4): 498–505. doi:10.1111/j.1469-7610.2008.01991.x. PMID 19017366.
- Laws, G.; Gunn, D. (2004). "Phonological memory as a predictor of language comprehension in Down syndrome: A five-year follow-up study". Journal of Child Psychology and Psychiatry, and Allied Disciplines. 45 (2): 326–337. doi:10.1111/j.1469-7610.2004.00224.x. PMID 14982246.
- Speidel GE. Herreshoff MJ. (1989). Imitation and the construction of long utterances. In G. E. Speidel & K. E. Nelson, (Eds), The many faces of imitation in language learning (pp. 181-197). New York, Springer-Verlag. ISBN 978-0-387-96885-8
- Kuczaj SA. (1983). Crib speech and language practice. New York, Springer-Verlag. ISBN 978-0-387-90860-1
- Scott, S. K.; McGettigan, C.; Eisner, F. (2009). "A little more conversation, a little less action — candidate roles for the motor cortex in speech perception". Nature Reviews Neuroscience. 10 (4): 295–302. doi:10.1038/nrn2603. hdl:11858/00-001M-0000-0013-2999-F. PMC 4238059. PMID 19277052. p. 201
- Fillmore LW. (1979). Individual differences in second language acquisition. In C. J. Fillmore, D. Kempler & W. S-Y. Wang, (Eds), Individual differences in language ability and language behavior (pp. 203-228). New York, Academic Press. OCLC 4983571
- Gathercole, S. E. (1995). "Is nonword repetition a test of phonological memory or long-term knowledge? It all depends on the nonwords". Memory & Cognition. 23 (1): 83–94. doi:10.3758/BF03210559. PMID 7885268. S2CID 20774241.
- Cheng, H (1996). "Nonword span as a unique predictor of second-language vocabulary learning". Developmental Psychology. 32 (5): 867–873. doi:10.1037/0012-1622.214.171.1247.
- Papagno, C.; Vallar, G. (1995). "Verbal short-term memory and vocabulary learning in polyglots". The Quarterly Journal of Experimental Psychology. A, Human Experimental Psychology. 48 (1): 98–107. doi:10.1080/14640749508401378. PMID 7754088. S2CID 19242688.
- Bishop, D. V.; North, T.; Donlan, C. (1996). "Nonword repetition as a behavioural marker for inherited language impairment: Evidence from a twin study". Journal of Child Psychology and Psychiatry, and Allied Disciplines. 37 (4): 391–403. doi:10.1111/j.1469-7610.1996.tb01420.x. PMID 8735439.
- Ojemann, GA (1983). "Brain organization for language from the perspective of electrical stimulation mapping". Behavioral and Brain Sciences. 6 (2): 189–230. doi:10.1017/s0140525x00015491.
- Kimura, D.; Watson, N. (1989). "The relation between oral movement control and speech". Brain and Language. 37 (4): 565–590. doi:10.1016/0093-934X(89)90112-0. PMID 2479446. S2CID 39913744.
- Shaffer LH. (1984). Motor programming in language production. In H. Bouma & D. G. Bouwhuis, (Eds), Attention and performance, X. pp. (17-41). London, Erlbaum. ISBN 978-0-86377-005-0
- Abbs JH. (1986). Invariance and variability in speech production, A distinction between linguistic intent and its neuromotor implementation. In J. S. Perkell, & D. H. Klatt, (Eds), Invariance and variability in speech processes (pp. 202-219). Hillsdale, NJ, Erlbaum. ISBN 978-0-89859-545-1
- Porter RJ. (1987). What is the relation between speech production and speech perception? In: Allport A, MacKay D G, Prinz W G, Scheerer E, eds. Language Perception and Production. London: Academic Press,: 85-106. ISBN 978-0-12-052750-2
- Hickok, G.; Poeppel, D. (2004). "Dorsal and ventral streams: A framework for understanding aspects of the functional anatomy of language". Cognition. 92 (1–2): 67–99. doi:10.1016/j.cognition.2003.10.011. PMID 15037127. S2CID 635860.
- Okada, K.; Hickok, G. (2006). "Left posterior auditory-related cortices participate both in speech perception and speech production: Neural overlap revealed by fMRI". Brain and Language. 98 (1): 112–117. doi:10.1016/j.bandl.2006.04.006. PMID 16716388. S2CID 1056984.
- Wise, R. J.; Scott, S. K.; Blank, S. C.; Mummery, C. J.; Murphy, K.; Warburton, E. A. (2001). "Separate neural subsystems within 'Wernicke's area'". Brain : A Journal of Neurology. 124 (Pt 1): 83–95. doi:10.1093/brain/124.1.83. PMID 11133789.
- Obleser, J.; Scott, S. K.; Eulitz, C. (2005). "Now You Hear It, Now You Don't: Transient Traces of Consonants and their Nonspeech Analogues in the Human Brain". Cerebral Cortex. 16 (8): 1069–1076. doi:10.1093/cercor/bhj047. PMID 16207930.
- Umiltà, M. A.; Kohler, E.; Gallese, V.; Fogassi, L.; Fadiga, L.; Keysers, C.; Rizzolatti, G. (2001). "I know what you are doing. A neurophysiological study". Neuron. 31 (1): 155–165. doi:10.1016/s0896-6273(01)00337-3. PMID 11498058.
- Hickok, G. (2010). "The role of mirror neurons in speech and language processing". Brain and Language. 112 (1): 1–2. doi:10.1016/j.bandl.2009.10.006. PMC 2813993. PMID 19948355.
- Skoyles, J. R. (2010). "Mapping of heard speech into articulation information and speech acquisition". Proceedings of the National Academy of Sciences. 107 (18): E73. Bibcode:2010PNAS..107E..73S. doi:10.1073/pnas.1003007107. PMC 2889576. PMID 20427741.
- Poizner H. Klima ES. Bellugi U. (1987). What the hands reveal about the brain. MIT Press. ISBN 978-0-262-66066-2
- Nishimura, H.; Hashikawa, K.; Doi, K.; Iwaki, T.; Watanabe, Y.; Kusuoka, H.; Nishimura, T.; Kubo, T. (1999). "Sign language 'heard' in the auditory cortex". Nature. 397 (6715): 116. Bibcode:1999Natur.397..116N. doi:10.1038/16376. PMID 9923672. S2CID 4414422.
- Goodale, E.; Kotagama, S. W. (2006). "Context-dependent vocal mimicry in a passerine bird". Proceedings of the Royal Society B: Biological Sciences. 273 (1588): 875–880. doi:10.1098/rspb.2005.3392. PMC 1560225. PMID 16618682.
- Putland, D. A.; Nicholls, J. A.; Noad, M. J.; Goldizen, A. W. (2006). "Imitating the neighbours: Vocal dialect matching in a mimic-model system". Biology Letters. 2 (3): 367–370. doi:10.1098/rsbl.2006.0502. PMC 1686190. PMID 17148405.
- Williams, H.; Nottebohm, F. (1985). "Auditory responses in avian vocal motor neurons: A motor theory for song perception in birds". Science. 229 (4710): 279–282. Bibcode:1985Sci...229..279W. doi:10.1126/science.4012321. PMID 4012321. S2CID 19053313.
- Klatt, D. H.; Stefanski, R. A. (1974). "How does a mynah bird imitate human speech?". The Journal of the Acoustical Society of America. 55 (4): 822–832. Bibcode:1974ASAJ...55..822K. doi:10.1121/1.1914607. PMID 4833078.
- Reiss, D.; McCowan, B. (1993). "Spontaneous vocal mimicry and production by bottlenose dolphins (Tursiops truncatus): Evidence for vocal learning". Journal of Comparative Psychology. 107 (3): 301–312. doi:10.1037/0735-7036.107.3.301. PMID 8375147.
- Foote, A. D.; Griffin, R. M.; Howitt, D.; Larsson, L.; Miller, P. J. O.; Hoelzel, A. (2006). "Killer whales are capable of vocal learning". Biology Letters. 2 (4): 509–512. doi:10.1098/rsbl.2006.0525. PMC 1834009. PMID 17148275.
- Ralls, K.; Fiorelli, P.; Gish, S. (1985). "Vocalizations and vocal mimicry in captive harbor seals, Phoca vitulina". Canadian Journal of Zoology. 63 (5): 1050–1056. doi:10.1139/z85-157.
- Poole, J. H.; Tyack, P. L.; Stoeger-Horwath, A. S.; Watwood, S. (2005). "Animal behaviour: Elephants are capable of vocal learning". Nature. 434 (7032): 455–456. Bibcode:2005Natur.434..455P. doi:10.1038/434455a. PMID 15791244. S2CID 4369863.
- Esser, K. H. (1994). "Audio-vocal learning in a non-human mammal: The lesser spear-nosed bat Phyllostomus discolor". NeuroReport. 5 (14): 1718–1720. doi:10.1097/00001756-199409080-00007. PMID 7827315.
- Wich, S. A.; Swartz, K. B.; Hardus, M. E.; Lameira, A. R.; Stromberg, E.; Shumaker, R. W. (2008). "A case of spontaneous acquisition of a human sound by an orangutan". Primates. 50 (1): 56–64. doi:10.1007/s10329-008-0117-y. PMID 19052691. S2CID 708682.
- Hayes C. (1951). The ape in our house, Harper, New York. OCLC 1579444