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Speech and Language

Speech and Language. Lecture for the 2 nd BM course Dr Jan Schnupp jan.schnupp@dpag.ox.ac.uk. What the syllabus says you should know ( § 20.4.3-20.4.5). Core material: Mechanisms of speech production Aphasias: Wernicke’s area and sensory aphasia; Broca’s area and motor aphasia.

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Speech and Language

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  1. Speech and Language Lecture for the 2nd BM course Dr Jan Schnupp jan.schnupp@dpag.ox.ac.uk

  2. What the syllabus says you should know (§20.4.3-20.4.5) • Core material: • Mechanisms of speech production • Aphasias: Wernicke’s area and sensory aphasia; Broca’s area and motor aphasia. • Hemispheric specialization • Extension Material: • Speech sounds and speech perception • Arcuate bundle. The dyslexias

  3. Part 1: Producing Speech

  4. Vocal Folds in Action http://mustelid.physiol.ox.ac.uk/drupal/?q=vocal_folds

  5. Articulators (lips, tongue, jaw, soft palate) move to change resonance properties of the vocal tract. https://mustelid.physiol.ox.ac.uk/drupal/?q=vocalization/articulators Articulation

  6. Harmonics and Formants of Speech Sounds Formant Harmonic

  7. Can other animals speak? • Other mammals have similar vocal tracts and use them for communication. However, they have only very limited use of syntax (grammar) and very much smaller vocabularies than humans. • http://mustelid.physiol.ox.ac.uk/drupal/?q=mishka

  8. Broca’s (Motor or Expressive) Aphasia • Patients with Broca’s Aphasia tend to understand speech well. • However, they have great difficulty articulating speech themselves, even though there is no severe paralysis of the articulators in the vocal tract. • Their speech tends to be halting, laboured, consisting of isolated utterances rather than full, grammatical sentences. • Suggests underlying cause is a difficulty in planning highly complicated motor acts.

  9. A Patient with Broca’s Aphasia • From the archives of the University of Wisconsin • http://mustelid.physiol.ox.ac.uk/drupal/?q=brocas_aphasia

  10. Broca’s Area • Broca’s aphasia is usually associated with lesion to the left frontal cortex. • See here the brain of Broca’s Patient, Mr Leborgne (“TanTan”) features a large lesion in Broca’s area.

  11. Part 2 – Hearing Speech

  12. Speech as a “Dynamic” Acoustic Signal • Most of the information in speech is carried in the manner in which the formant structure varies over time. • Pitch carries little or no semantic information (but is important in prosody and in “pitch tracking” for speech in noise. • Think of the role of the tonotopic axis in the ascending auditory pathway as representing formant distributions. (Not pitch!)

  13. To make speech comprehensible, cochlear implants reproduce the formant structure as a pattern of electrical stimulation along the tonotopic axis of the Basilar Membrane. https://mustelid.physiol.ox.ac.uk/drupal/?q=prosthetics/noise_vocoded_speech Speech and Cochlear Implants

  14. Spectrogram (B) and Auditory (VIII) Nerve “Neurogram” (A) of a spoken sentence. • From Delgutte B (1997) Auditory neural processing of speech. In: The Handbook of Phonetic Sciences (Laver WH, ed), pp 507-538. Oxford: Blackwell.

  15. Auditory Cortex Neurograms of American English Onset Consonants (Engineer et al. Nat Neurosci 2008)

  16. Where in the Brain does the Transition from Sound to Meaning happen? • We don’t really know. • “Ventral vs Dorsal stream hypothesis” of auditory cortex connectivity would suggest that anterior temporal and frontal structures should be involved. • This fits with neuroimaging studies (e.g. Scott et al (2000) Brain 123 Pt 12:2400-2406) • https://mustelid.physiol.ox.ac.uk/drupal/?q=node/46 • But other electrophysiological and lesion data do not really fit this picture.

  17. Part 3 More about Aphasias and Clinical Observations

  18. Receptive (Wernicke’s Aphasia) • Patients with Wernicke’s Aphasia usually have great difficulty understanding speech, even though there is no deafness. • They may speak fluently, often in long sentences, but the meaning of their sentences is unclear. (“fluent paraphasia”).

  19. A Patient with Wernicke’s Aphasia • From the archives of the University of Wisconsin

  20. Wernicke’s Area • Wernicke’s aphasias are often associated with lesions at the boundary of the superior temporal and parietal lobes on the left hemisphere.

  21. Conduction Aphasia • Patients may be able to understand speech as well as produce meaningful speech, but have difficulty repeating a spoken sentence. • Often associated with damage to the Arcuate Fasciculus, which connects Wernicke’s area with frontal pre-motor structures.

  22. The Arcuate Fasciculus Big fibre bundle connecting Broca’s and Wernicke’s Areashttp://www.biocfarm.unibo.it/aunsnc/pictef14.html

  23. Categorizing Aphasias • Brain lesions are rarely confined to particular “classical” area boundaries. • The symptoms used to diagnose and classify aphasias can vary considerably in severity. • Thus, aphasic patients may not fit the diagnostic categories terribly well, and the way aphasias are categorized are themselves evolving.

  24. Cortical Speech Areas and Neurosurgery • Surgeons attempting to remove epileptic foci or tumours from the brain are anxious to avoid damaging areas that are crucial for speech production or comprehension. • They may use “Wada tests” or temporary functional lesioning trough direct electrocortical stimulation. • Further reading: Calvin & Oja “Conversations with Neil’s Brain”.

  25. Hemispheric “Dominance” for Speech and the Wada test • Broca first proposed that the left hemisphere is “dominant” for speech, based on examinations of post-mortem brains. • Nowadays “dominance” is usually assessed with the “Wada test” (intracarotid sodium amobarbital procedure): either the left or right brain hemisphere is anesthetised by injection of amobarbital into the carotid through a catheter. The patient’s ability to understand and produce speech is scored.

  26. Left Hemisphere Dominance Dominates Wada test results suggest that: • Ca 90% of all right handed patients and ca. 75% of all left handed patients display “left hemisphere dominance” for speech. • The remaining patients are either “mixed dominant” (i.e. they need both hemispheres to process speech) or they have a “bilateral speech representation” (i.e. either hemisphere can support speech without necessarily requiring the other). • Right hemisphere dominance is comparatively rare, and seen in no more than 1-2% of the population

  27. Hierarchical levels of speech perception • Acoustic / phonetic representation:- Can the patient tell whether two speech sounds or syllables presented in succession are the same or different? • Phonological analysis:- Can the patient tell whether two words rhyme? Or what the first phoneme (“letter”) in a given word is? • Semantic processing:- Can the patient understand “meaning”, e.g. follow spoken instructions?

  28. “Functional Lesioning” by Electrocortical Stimulation • Sites where direct electrical stimulation can disrupt acoustic/phonetic (A), phonological (B) or semantic (C) processing of speech. • From Boatman D (2004) Cortical bases of speech perception: evidence from functional lesion studies. Cognition 92:47-65.

  29. If you want to know more • Try chapters 1,2, 4 and 8 of “Auditory Neuroscience” by Schnupp, Nelken & King, MIT Press. • Check out auditoryneuroscience.com

  30. That’s all Folks

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