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Language Processing and the Human Brain - Coggle Diagram
Language Processing and the Human Brain
Psycholinguistics
Concerned with linguistic performance > how we use our linguistic competence in speech or sign production and comprehension.
Performance limitations:
Our language competence can cope despite all kinds of performance problems. Performance is not always a true reflection of competence.
Memory limitations
Sentence complexity, double negation, and different kinds of information packaging
Noisy data (false starts, hesitations, repetitions, incomplete sentences)
Sheer speed of speech (20 phonemes per second).
Limitations allow us to hear and process phonetic signals, to get words from the mental lexicon, and to construct a phrase structure representation of the words we retrieve.
The speech signal
Understanding a sentence = comprehending the individual speech sounds
The acoustic signal
The fundamental frequency of the sounds > pitch
The magnitude/intensity of the variations > loudness
Spectrograms (produced by a computer program)
Spectrograms (produced by a computer program)
How does the listener carve the continuous speech signal into meaningful units? (segmentation problem)
How does the listener manage to recognise particular speech sounds when they occur in different contexts and when they are spoken by different people? (invariance problem)
The interface between our knowledge of the world and our linguistic knowledge is our knowledge of vocabulary.
Separating the words in a speech stream is the segmentation problem, but searching the mental lexicon is a process known as lexical access.
Prosodic clues: the stress and intonation of words help in segmenting the speech stream.
bottom-up/top-down models
Top-down > using the semantic and syntactic information, then leading to an interpretation of the sensory input
Evidence found in word-identification experiments
Shadowing: subjects repeat what they hear as rapidly as possible
Fast shadowers are usually about a syllable behind the speaker, and if the speaker makes an error, the shadower will often correct them > unconscious anticipation/prediction of the input based on semantic/syntactic information, then leading to the sensory input.
Word identification:
Subjects make more errors when the words they are to identify occur in isolation than when they occur in sentences.
Suggests that we use our knowledge of units larger than the words to make sense of utterances.
Bottom-down > using the incoming acoustic signal to then put together the semantic interpretation.
Phoneme restoration
Buzz or click experiments provide evidence for phoneme restoration > buzz or click overlaps person talking, but the person listening can fill in the missing phoneme despite not hearing it.
People can recognise the sounds that were overshadowed, and believe that they heard it when they didn’t.
Lexical access and word recognition
The process by which we obtain information about the meaning and syntactic properties of a word from our mental lexicon.
Experimental techniques
Lexical decision tasks > tasks in which participants must indicate whether a written or spoken stimulus is a word or a non-word.
Used to use response time, but is now not considered accurate, because measuring brain activity usually contradicts findings.
Priming tasks > tasks that exploit the fact that words can be activated by hearing semantically-related words.
Naming tasks
People read irregularly spelt words more slowly than they read words that follow regular rules, but faster than nonsense words.
It seems that the mind notices the irregularity and tries to do two tasks at once in parallel (lexical look-up and sounding out the word) > resolving the inconsistency takes longer.
Speech production
Planning units > speech errors show that features, segments, words and phrases may be conceptualised well before they are uttered
Pre-planning involves units larger than the phoneme and even the word (top-down)
Experiments are difficult to devise > most evidence comes from natural, spontaneous speech
Lexical selection > blends illustrate the lexical selection process in speech production
Application and misapplication of rules > rules of morphology and syntax may be applied (or misapplied when we speak)
Neurolinguistics
Neurolinguistics is the study of the biological and neural foundations of language > the brand of linguistics concerned with the brain mechanisms that underlie the acquisition and use of human language.
The brain
The average human brain weighs about 1400 grams
A whale’s brain weighs about 9000 grams
Humans have the highest brain-to-body ratio (dolphins are the second highest)
The brain is pink-ish white at birth and turns grey with age.
The brain is made up of neurons, the basic information-processing units of the nervous system
There are about 10 billion neurons, organised into networks. Each neuron can be linked up to 10,000 other neurons.
The brain is also made up of structures which seem to play an important role in the integrated functioning of the brain.
When we talk of the brain, we talk of all of the structures above the spinal cord: the medulla oblongata, the pars Varolii, the cerebellum and the cerebral cortex.
Form an integrated whole by means of neural connections
The first three (hindbrain) are concerned with physical bodily functions > breathing, heartbeat, transmission and coordination of movement, digestion, involuntary reflexes and emotional arousal.
Cerebral cortex:
Outside surface of the brain, about 6mm deep
A layer of grooved, wrinkled tissue that fits like a cap over the rest of the brain.
65% of it is folded inwards, allowing a huge amount of matter to be fit into a very small area
Sulci and gyri (dips and rises)
The human brain develops from the bottom up, and the cerebral cortex is a relatively recent evolutionary development.
Has four lobes: frontal, temporal, parietal and occipital.
Where language representation and processing take place
Responsible for decoding information from the senses
Responsible for most voluntary movements we make.
Reptiles and amphibians have no cerebral cortex, fish have little ones.
Cerebral hemispheres
The physical separation of the two brain hemispheres can be seen by the naked eye > a very deep sulcus, called the longitudinal fissure, separates the two hemispheres.
The hemispheres are connected by a bundle of nerves called the corpus callosum, allowing the two hemispheres to communicate with each other.
Larger in women and gay men
lateralisation
Any cognitive function that is localised primarily on one side of the brain
The two hemispheres can be thought of as a separate brain, and are often called the left and right brains.
Both hemispheres are involved in control over muscular activity, sight, and hearing.
The left and right hemispheres are functionally distinct to an extent > hemispheric specialisation
Left
: speech, language and comprehension, analysis and calculations, recognition of words, letters and numbers, fine judgments of temporal order
right
: creativity, spatial ability, context/perception, recognition of faces, places and objects, singing (can sing even if left-hemisphere damage causes speech impairment), interpretation of tone and intonation that signals emotions (damage makes it harder to understand metaphorical utterances).
The right hemisphere has some involvement in early language development, and there are instances where it can take over normal left hemisphere function if brain damage or surgery occurs early in life.
Dominance
: the functional relationship between hemispheres has been a major focus of research. Each hemisphere is more involved in some activities and less in others.
Contralaterality
: sensory + motor from right side of body is controlled by left hemisphere, sensory + motor from left side of body is controlled by right hemisphere
Cerebral asymmetry:
functional asymmetry of the cerebral hemispheres is economical, enabling the brain tissue to perform a wider variety of functions than would be possible if each hemisphere were a replica of the other.
The potential for each to replicate the other provides a backup for the nervous system.
Senses
:
The signals from each ear go to both hemispheres, but most input is transferred to the opposite side
Ipsilateral inputs are weaker
The left side of the visual field of each eye transmits information to the right side and vice versa
Handedness
Language is said to be located in the left hemisphere regardless of handedness
Language dominance is in the left hemisphere for 99% of right-handers and about two-thirds of left-handers.
Left-handers are not right-lateralised for language; they are less lateralised for language > showing both left and right hemisphere involvement in language functioning and a more even distribution of responsibilities for languages.
Split brains
Studies of humans who have undergone split-brain operations have found that the two hemispheres appear to be independent.
Hemisphere functions in children
In the case of kids up to age 5 who have had brain damage in the left hemisphere, it is generally the case that the left hemisphere functions are taken over by the right hemisphere.
The older you are when the damage occurs, the less chance there is of this happening.
Some adults who had lost some or all of the functioning of their left hemisphere, either through damage or surgical removal, seem to have some (not much) language available. Typically, they retain some comprehension ability.
Aphasia
Any language disorder that results from brain damage caused by disease or trauma.
How we can tell that the hemispheres and different parts of the brain do different things > impairment in a certain skill due to damage in a certain area.
People with aphasia are not good at sequencing (temporal) or complex motor sequences, and therefore, the complex, voluntary movements necessary for speech may be implicated in speech issues.
Broca’s and Wernicke’s areas
Broca's area is responsible for organising the articulatory patterns of speech. It lies very close to the area of the cortex that controls the muscles of the face, jaw, tongue, palate, and larynx.
The use of inflections and function words is also governed by Broca’s area, this region is crucial for formation of words and sentences.
Wernicke’s area is close to the auditory cortex. Therefore, it is important in the representation of meaning and interpretation and selection of words.
Broca’s (agrammatic) aphasia
: Laboured speech, word-finding difficulties, lack of function words, inflection omissions, difficulties understanding complex sentences
Wernicke’s (severe jargon) aphasia
: Fluent speech, semantically incoherent, difficulty naming things, numerous lexical errors, jargon and nonsense words.
Brain imaging technology
Computed tomography (CT)
Magnetic resonance imaging (MRI)
Positron emission tomography (PET)
Functional magnetic resonance imaging (fMRI)
Magnetoencephalography (MEG)
Measures the magnetic field generated by the brain
Experiments have shown that the brain reacts differently to sounds that are phonemically different than to sounds that are acoustically different but non-phonemic.
Such results are taken as evidence that the theoretical approaches adopted in linguistics have strong biological plausibility.
Event-related potentials (ERPs)
Electrical signals are emitted from the brain in response to different stimuli
ERP experiments have shown similar variations in timing, pattern, amplitude and hemisphere of response when participants hear sentences that are meaningless compared to meaningful sentences
Results are taken as evidence that the left hemisphere is sensitive to grammatical structure even in the absence of meaning.
Critical period
Critical-age hypothesis
Language is biologically based; the ability to learn a native language develops within a fixed period, from birth to middle childhood.
After this critical period, the acquisition of grammar is difficult and not entirely achieved.
Genie
Discovered in 1970
Minimal human contact from 18 months to 14 years
She acquired a large vocabulary
Her syntax and morphology never developed