05 Speech Perception
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Transcript of 05 Speech Perception
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Language !Speech
! Speech is the preferred modality for language.
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Outer ear
Collects sound waves. Theconfiguration of the outer
ear serves to amplifysound, particularly at
2000-5000 Hz, afrequency range that is
important for speech.
Middle ear
Transforms the energy of a
sound wave into the internalvibrations of the bone
structure of the middle ear
and transforms thesevibrations into a
compressional wave in the
inner ear.
Inner ear
Transform the energy of acompressional wave within
the inner ear fluid intonerve impulses which can
be transmitted to the brain.
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http://www.sis.pitt.edu/~is1042/html/audtrans.gif
Auditory
input reaches
primary auditorycortex about
1015 msec after
stimulus onset
(Liegeois-Chauvel,
Musolino,
& Chauvel, 1991;Celesia, 1976).
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http://ist-socrates.berkeley.edu/ ~jmp/LO2/6.html
Primary auditory cortex (A1): Brodmann areas 41 and 42.Auditory-association cortex (A2): Brodmann area 22.
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Questions
! Is speech special?" Is there brain activity that is specifically sensitive
to the properties of speech (as opposed to those ofother sounds)?
" Can brain damage lead to a selective loss of speech
perception?
" Are the mechanisms of speech perception different
from the mechanisms of auditory perception ingeneral?
! Role of audio-visual integration
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An auditory evoked neuromagnetic field
Roberts, Ferrari, Stufflebeam & Poeppel, 2000, J Clin Neurophysiol, Vol 17, No 2, 2000
M100 field pattern
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M100 (N1 in ERP terms)
! Intensity
" higher intensity "shorter latency, larger amplitude
! Frequency" higher frequency "shorter latency
! Phonetic identity
" e.g., shorter latencies for athan for u(explainable inspectral terms)
! Function of M100 activity in speech processing
unclear.
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M100 (N1 in ERP terms)
(Roberts & Poeppel, Neuroreport, 1996)
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M100 (N1 in ERP terms)
(Poeppel et al., Neuroscience Letters, 1996)
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Questions
! Is speech special?" Is there brain activity that is specifically sensitive
to the properties of speech (as opposed to those ofother sounds)? Unclear.
" Can brain damage lead to a selective loss of speech
perception?
" Are the mechanisms of speech perception different
from the mechanisms of auditory perception ingeneral?
! Role of audio-visual integration
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Questions
! Is speech special?" Is there brain activity that is specifically sensitive
to the properties of speech (as opposed to those ofother sounds)? Unclear.
" Can brain damage lead to a selective loss of speech
perception?
" Are the mechanisms of speech perception different
from the mechanisms of auditory perception ingeneral?
! Role of audio-visual integration
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Disorders of auditory processing
! Rare.
! Signal from each ear
is processed in bothhemispheres (contravisual system).
! Bilateral damage oftennecessary." Generally requires
two separate
neurological events.
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! Inability to hear sounds without apparent damageto the hearing apparatus or brain stem
abnormality.! Extensive bilateral damage to auditory cortex
(BAs 41 & 42).
Disorders of auditory processing:
CORTICAL DEAFNESS
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! Inability to recognise auditorily presented sounds
(e.g., coughing, crying)independent of any deficit in
processing spoken language.
! Damage in auditory association cortex (BAs 22 &
37)
Disorders of auditory processing:
AUDITORY AGNOSIA
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! Impaired in tasks requiring pattern recognition in
music.
! Relative sparing of speech and (other) non-speech
perception.
! Damage generally in righttemporal areas.
Disorders of auditory processing:
AMUSIA (a subvariaty of AUDITORY AGNOSIA)
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! Inability to understand spoken words while
" auditory perception is otherwise intact &
" other linguistic skills are intact (reading, speech
production)
Disorders of auditory processing:
PURE WORD DEAFNESS
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Either
! Bilateral damage to auditory
cortex
Or
! A subcortical lesion in the lefthemisphere that severs bothipsilateral and contralateralprojections to Wernickes area(Ziegler,1952; Geschwind, 1965; Coslet et al.,
1984; Jones and Dinolt, 1952).
Disorders of auditory processing:
PURE WORD DEAFNESS
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! Impairment in the ability to recognise familiar
voices." Speech comprehension is intact.
" Intact ability to identify nonverbal sounds.
Disorders of auditory processing:
PHONAGNOSIA
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! Van Lancker et al., 1988: Double dissociation between
memory for familiar voices and the ability to discriminate
between unfamiliar voices.
Disorders of auditory processing:
PHONAGNOSIA
! Performance on a
discrimination task was
impaired by a lesion to either
temporal lobe.
! Performance on the famous
voices task was impaired by
lesions to the right parietal
lobe.
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Questions
! Is speech special?" Is there brain activity that is specifically sensitive
to the properties of speech (as opposed to those ofother sounds)? Unclear.
" Can brain damage lead to a selective loss of speech
perception? YES, but no one-to-one correspondence
between lesion site and type of disorder. E.g.,
bilateral temporal damage can lead either to
cortical deafness or pure word deafness.
" Are the mechanisms of speech perception different
from the mechanisms of auditory perception in
general?
! Role of audio-visual integration
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Poeppel (2001), Poeppel & Hickok (2000):
! Speech is fundamentally bilateral.
! But LH and RH have different temporal integrationwindows.
" LH processes fast phenomena, 25-50ms
! Acoustic changes in frequency that allow phoneme perception.
" RH processes slow aspects of speech, 150-200ms.
! Syllable level phenomena. Intonation. Prosody.
Bilaterality of speech processing
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Questions
! Is speech special?" Is there brain activity that is specifically sensitive
to the properties of speech (as opposed to those ofother sounds)? Unclear.
" Can brain damage lead to a selective loss of speech
perception? YES, but no one-to-one correspondence
between lesion site and type of disorder. E.g.,
bilateral temporal damage can lead either to
cortical deafness or pure word deafness.
" Are the mechanisms of speech perception different
from the mechanisms of auditory perception in
general?
! Role of audio-visual integration
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What makes speech sound like speech?
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Sine-wave speechA spectrogram, or anacoustic "picture" of aspeech utterance. Time is
represented on the
horizontal axis, frequency onthe vertical axis. Amplitudecorresponds to the darkness.
A sinewave replica of thenatural above. All fine-
grain acoustic propertiesof speech are discardedand only the coarse-grainchanges in the spectraover time are retained.
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Sine-wave speech! Remez et al. (1981):
"Nave subjects fail to perceive sine-wave
stimuli as speech.
"However, if subjects are instructed aboutthe speech-like nature of sinewave speech,
they can easily understand it.
"Argument for a special speech mode of
processing.
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Sine-wave speech
OriginalSWSSentence 6
OriginalSWSSentence 5
OriginalSWSSentence 4
OriginalSWSSentence 3
OriginalSWSSentence 2
OriginalSWSSentence 1
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Role of articulatory gestures on speechperception! Recognition of sine-wave speech or speech that
has been degraded by noise is improved if thestimulus is accompanied by congruent
articulatory gestures.
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McGurk effect
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Role of articulatory gestures on speechperception! Incongruent articulatory gestures can changethe
auditory percept even when the signal is clear.
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Is audio-visual integration specific to speech?! Saldana and Rosenblum (1993): No.
" Audiovisual integration of the plucks and bows
of cello playing.
#Not only speech, but also other ecologically validcombinations of auditory and visual stimuli canintegrate in a complex manner.
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Question! Is speech is perceived as all other sounds or is there a
specialized mechanism responsible for coding theacoustic signal into phonetic segments?
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Method experiment 11. Training in non-speech mode: Subjects were first trained to
distinguish between Stimulus 1 and 2, which were the sinewavereplicas of the Finnish nonwords /omso/ and /onso/.
2. Non-speech test:SWS tokens were presented alone or audio-visually with a congruent or incongruent visual articulation.
Subjects were instructed to indicate by a button press whether theyheard stimulus 1 or 2.
3. Natural speech test:As in 2, but now the auditory stimuliconsisted of natural tokens of /onso/ and /omso/. Subjects were toldto indicate whether the consonant they heard was /n/, /m/ or
something else.4. Training in speech mode:Subjects were taught to categorize the
SWS stimuli as /omso/ and /onso/.
5. Test in speech mode:Indicate whether the consonant they heardwas /n/, /m/ or something else.
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Results
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Experiment 2: Speech mode training andtest occur first
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Questions
! Is speech special?" Is there brain activity that is specifically sensitive
to the properties of speech (as opposed to those of
other sounds)? Unclear.
" Can brain damage lead to a selective loss of speech
perception? YES, but no one-to-one correspondence
between lesion site and type of disorder.
" Are the mechanisms of speech perception different
from the mechanisms of auditory perception in
general?
! Role of audio-visual integration may be special forspeech.