Week 10 Flashcards
Cerebral Lateralisation
Brains are asymmetrical
• Anatomically (gross and micro level)
• Neurochemically
• Functionally
Anatomical Asymmetry
• Right further forward • Left further back • Right frontal wider • Left occipital wider • Longitudinal fissure to right of midline (post) and left (ant) Perisylvian asymmetry • Left sylvian fissure longer and less sloped • Left Wernicke larger • Neurons in left Broca more synaptic connections • Left angular gyrus larger • Right parietal area larger
Neurochemical Asymmetry
Left - dopamine • Basal ganglia – complex motor • Right handedness Right – noradrenaline • Thalamus – arousal system • Maintains alertness • Integrates bilateral perceptual information • Spatial
Functional Asymmetry
People are NOT left brain or right brain
• Biases rather than absolute differences
• Language most lateralised of cognitive abilities, but not
total
• Handedness
• Apraxia almost always with left lesions, but bilateral
symptoms
• Neglect – mostly right lesions / left neglect
• Differences between people – correlated with
handedness and gender
Functional Asymmetry
Left • Language – speech, reading, writing, arithmetic • Complex movement • Word recognition (FWA) • Recognition of local features Right • Language – emotional content • Spatial – mental rotation, geometry, direction, distance • Facial recognition (FFA) • Global features Handedness • 10% left handed • 70% of left handed have same lateralisation as right hander (15% reversal; 15% bilateral) • 97% right handers but 70% left handers have left language • Left language emerged from left dominance of motor??
Cerebral Lateralisation
• Lateralization conserved or independently acquired
during evolution suggests it provides an advantage
• MRI studies correlate the strength of functional
lateralization with the level of cognitive ability
• Brain lateralization might provide benefits by allowing
the hemispheres to perform parallel tasks
• Reflect evolutionary, hereditary, developmental,
experiential, and pathological factors
• Variation in the development of brain asymmetry is
suspected to contribute to various
neuropathologies
• Autism and dyslexia are associated with atypical
patterns of functional and structural asymmetries
• Left- or mixed-handedness increased from 10% in
the general population to 20% - 40% in
schizophrenic patients.
Language Introduction
• Communication – transfer of information by speech,
signals, writing, or behaviour
• Function of language – influence behaviour of others
by changing what they know, think, believe, or desire
• Language depends on rules rather than learning
sequences and/so is generative (can create and
understand endless variations)
• Animals – complex songs or distinct warning calls for
different threats but don’t combine calls for new ideas
Animal Communication - Vocal
• Calls with specific meaning (e.g. vervet monkeys)
• Snake call – stand up and look down
• Leopard call – scamper into trees
• Bird call – run from exposed branches to huddle near trunk
• Not just reflexive reactions to situations – depend on
social context
• Vervet monkeys don’t make alarm calls if no other
monkeys nearby – more likely if nearby are relatives
• Production vs comprehension – best animals can
produce only a few calls but most animals can
understand/interpret lots of environmental sound -
comprehension seems older and widespread
• Vocal – involuntary signals associated with
emotional state in response to specific stimulus
and broadcast to group
Animal Communication - Gestural
• More flexible and non-urgent
• initiate playing and grooming with a specific individual
• some learned socially
• Gestures require knowing the attentional state of
the partner – shared attention
• Little cortical control over vocalisations
• Excellent cortical control over hands and arms
• Language evolved from gestural (Tomasello;
Corballis)?
• Teaching chimps sign language rather than to speak
• Chimps and bonobos have right hand preference
(left hemisphere) for communication gestures but
not for non-communicative gestures
Language Functional Levels
• Basic sounds (phonemes) create sematic units
(morphemes) – smallest grammatical unit
• Morpheme can be a word but not necessarily – e.g.
‘bookkeepers’ has 4 morphemes – ‘book’ and ‘keep’;
‘er’ and ‘s’
• Each language has set of phonemes and rules to
combine to create morphemes and words (‘zb’)
• Words combined by rules of syntax into sentences
(grammar includes syntax and other stuff)
Prosody
• The patterns of stress and intonation in a language
• Prosodic cues – pitch, duration and loudness changes
• Linguistic information in tonal languages (e.g. Chinese,
Vietnamese, Thai) (left hemisphere)
• Paralinguistic information – emotion (right hemisphere)
• Task of understanding
• Decode auditory stream into phonemes
• Join phonemes appropriately into morphemes
• Build morphemes into words and words into sentences
• Extract conceptual meaning from words, order,
context, prosody, earlier sentences
• Task of production
• Essentially the reverse
• Translate high-level concepts into string of phonemes
then accurately produce the sounds
Language Acquisition
• Easily acquire language – just need exposure (reading –
have to actively learn)
• Acquisition in children follows a universal pattern and
typically developing master by 3 years
• Skinner – language acquired through learning –
monitoring and management of reward (reinforcement
learning)
• Chomsky - innate language faculty with universal
grammar and phonetics, exposure to a specific
language triggers selection process
• Recent – not quite either – learning but different to
external shaping and reinforcement
• Learn language through detailed and sophisticated
analysis of the language they hear to reveal
underlying patterns; learning the patterns then
alters perception to favour the native language
• Listening to language alters infant brain early in
development
• Speech perception and speech production develop in
parallel (perception leads production)
• Universal infant then specialise to native language
• Universal perception before 6 months - discern slight
acoustic changes at phonetic boundaries for all
languages (adult only for fluent language)
• Universal production before 10 months – babble then
specific language patterns
Speech Production
• Well before produce words, learn sound patterns
underlying phonetic units, words and phrase
structure of language they hear
• Just before first words – non-native discrimination
declines rapidly but native improves significantly –
become specialist
• 10 months – no speech (babble)
• 12 months – 50 words and begin to produce
speech that resembles native language
• Approach 24 months – mimic sound patterns of
native – pitch, rhythm
• 3 years – 1000 words (adult 70k) and can create
long sentences and have a conversation
• Prosodic cues – pitch, duration and loudness changes –
learn global sound patterns early (prosodic patterns
transmitted in utero but sound patterns for words not)
• 7-8 months recognise words using probability that one
syllable follows another – probabilities between syllables in
a word are high (‘ta’ follows ‘po’ in potato) but between
words are low (‘po’ follows ‘hot’ in hot potato)
• 9 month old show listening preference for native, 6 month
not
• 30 months – readily discriminate only sounds that compose
language exposed to (native language)
• Expose American
infants (9-10 months)
to Mandarin
• Learn if interaction
with human
• Not if same material
through TV or audio
• Human group as good
as infants raised in
Taiwan for full 10
months
• Motherese (parentese) – higher pitch, slower
tempo, exaggerated intonation when speaking to
infants and young children
• Fairly universal
• Given a choice, infants prefer listening to parentese
over adult-speak
Critical Period
• Second half of the first year - learning native language
produces neural commitment to acoustic patterns –
tuning
• Maturation sets the time when the learning window
opens
• Experience determines when the window closes
• Neural commitment enhances ability to detect learned
patterns and reduce ability to detect those that don’t
conform
• Motor patterns for native language interfere with
efforts to pronounce new language - accent
• Once discrimination to non-native language lost (30
months) hard to regain (learning a language as an
adult)
• Second language learning improved by training that
mimics early acquisition
• Long periods of listening in social context (immersion)
• Use of auditory and visual information
• Exposure to simplified and exaggerated speech (parentese)
Lateralisation
• Left lateralisation of language in 95%
• Left specialised for phonetic, word and sentence
processing (separate production and
comprehension areas)
• Prosody engages left and right depending on
information conveyed – linguistic (semantic
information in tonal languages) left; emotional,
right
• Right lesions can produces emotionally flat speech
with inappropriate stress, timing and intonation
(also fail to interpret emotional cues in others
speech)
• Right also in discourse – meaning over many
sentences – right lesions difficulty in ordering
sentences into coherent narrative; problems
understanding when meaning requires
relationships among sentences (e.g. fail to get
jokes)
Classical Model
• Language circuits and areas first identified through
studies of aphasia (no animal models, imaging recent)
• Aphasia
• Language deficits (comprehension and/or production)
• Neurological damage but articulatory mechanisms intact
• Loss of control of articulatory muscles is dysarthria
• Problems with motor planning of speech is apraxia
• 40% of all strokes produce some aphasia but may be
transient
• Begin with Broca – inferior portion of left PFC is
centre for speech production (Broca’s area - BA)
• Wernicke – language area in left temporal lobe just
posterior to A1 is the centre of language
comprehension (Wernicke’s area - WA)
• WA is connected to BA via the arcuate fasciculus
(AF)
