Lecture 18 - Language PDF

Introduction to Behavioral Neuroscience PSYC 211 Lecture 18 of 24 – Language Textbook Chapter 13 Professor Jonathan Britt Questions? Concerns? Please write to [email protected]  SPEECH COMPREHENSION Lateralization...

Introduction to Behavioral Neuroscience PSYC 211 Lecture 18 of 24 – Language Textbook Chapter 13 Professor Jonathan Britt Questions? Concerns? Please write to [email protected]  SPEECH COMPREHENSION Lateralization Verbal behavior is lateralized in the brain. Most language disturbances (comprehension and expression) occur after damage to left side of brain. The left hemisphere is dominant for speech in 90 percent of the population (94% of right-handed people and 70% of left-handed people).  PROSODY: RHYTHM, TONE, AND EMPHASIS Human speech has a regular rhythm and cadence People emphasize certain words (i.e., pronounce them louder) to clarify what they mean People change the pitch of spoken words to indicate phrasing and to distinguish between assertions and questions Altogether, the rhythm, emphasis, and tone of speech is known as prosody. People impart information about their emotional state through prosody. Prosody is typically a function of the right hemisphere, so people with left hemisphere damage who struggle with language comprehension will typically still be able to extract information from prosody (such as the emotional state of the speaker and whether they are asking question).  RECOGNITION OF PEOPLE'S VOICES People can recognize the voice of familiar individuals. Even newborn infants recognize the voices of their parents. Voice recognition is independent of word comprehension. People with left hemisphere brain damage can often recognize voices even they cannot understand language. Phonagnosia, a disorder where people have difficulty recognizing voices, results from damage to the right cerebral cortex (temporal lobe).  UNFAMILIAR METAPHORS Attempts to understand unfamiliar metaphors strongly activates the right hemisphere The left hemisphere is often needed to understand the literal meaning of words, whereas the right hemisphere is involved in understanding metaphorical language.  APHASIA Aphasia refers to a disturbance in understanding, repeating, or producing meaningful speech. The difficulty must not be caused by simple sensory or motor deficits or by lack of motivation. The deficit must be relatively isolated, such that the patient must be capable of recognizing when others are attempting to communicate. The patient must be somewhat aware of what is happening around them. All the following slides relate to brain damage in the left cerebral hemisphere (for most people).  MIDDLE CEREBRAL ARTERY Damage to this artery often results in an aphasia. Symptoms vary massively according to where exactly the cell death occurred.  Damage to sensory association cortex APHASIA causes deficits in understanding language. Names for this type of aphasia include: posterior aphasia sensory aphasia receptive aphasia Wernicke’s aphasia fluent aphasia Damage to the frontal lobe causes deficits in speaking and writing. Names for this type of aphasia include: anterior aphasia motor aphasia expressive aphasia Broca’s aphasia non-fluent aphasia  WORD COMPREHENSION When you hear, speak, read, or write the word DOG, do you understand what this word means? VISION – What do dogs look like? AUDITORY – What do dogs sound like? TOUCH – What do dogs feel like? OLFACTION – What do dogs smell like? GUSTATORY – What do dogs taste like? MOTOR – What do dogs act like? What does petting a dog entail?  ASSOCIATION CORTEX What does a dog feel like? What does petting a dog entail? What does a dog look like? What does a dog sound like?  LANGUAGE AREAS Texture of a dog Writing Brail word perception M1 S1 Spoken word perception hand hand (Wernicke’s Area) M1 mouth A1 Sight of a dog Speaking V1 Written word (Broca’s Area) perception Word choice (VWFA) Sequencing Grammar Articulation Sound of a dog (barking)  WORD COMPREHENSION The posterior language area (pink) is critical for language comprehension. Neurons here probably activate the ensemble of neurons throughout sensory association cortices that store the representations (the meanings) of specific words. For example, activating the DOG neurons here would cause activity throughout sensory association cortices (vision, hearing, touch, smell, taste, and motor) that are associated with the word DOG.  WORD COMPREHENSION The posterior language area is located at the junction of the temporal, occipital, and parietal lobes. It is critical for language comprehension (regardless of whether words are heard, spoken, or read). Damage to the posterior language area causes Transcortical Sensory Aphasia: Failure to comprehend the meaning of words and an inability to express thoughts with meaningful speech. Word perception and speaking might be fine (but with limited comprehension of what is heard or said). For example: Word repetition (e.g., repeat after me…) is frequently observed. Reading (without understanding) is possible. Writing (without understanding) is possible. RECEPTIVE, FLUENT APHASIA  BYRON’S ROAD TO RECOVERY Byron’s wife, 5 years after her husband’s stroke: They told me he had Wernicke’s aphasia. I didn’t know what that meant, but I knew his speech made no sense. At first, I was told that all improvement would come within 90 days. Many families get this kind of information – it simply isn’t true. The truth is that improvement can always happen, and does, but it’s unlikely Byron will ever get back to 100%. Currently Byron understands over half of what he hears, and he can understand what he reads in a book or newspaper. Byron cannot spell or repeat words. He can read numbers, do math problems, make change, and analyze a financial statement better than I can. So, from 0% comprehension and “word salad” to 60% comprehension and some functional language is not bad in 5 years. We have a long way to go, but the road is getting shorter all the time. Never give up. Never accept “no” for an answer. Always keep searching for new ideas on aphasia. Don’t stay home. Be adventurous!  ALL LANGUAGE PERCEPTION AREAS CONNECT TO THE POSTERIOR LANGUAGE AREA Writing M1 Spoken word perception hand hand (Wernicke’s Area) M1 mouth A1 Speaking V1 Written word (Broca’s Area) perception Word choice (VWFA) Sequencing Grammar Articulation  ALL LANGUAGE PERCEPTION AREAS DIRECTLY CONNECT TO BROCA’S AREA Writing M1 Spoken word perception hand hand (Wernicke’s Area) M1 mouth A1 Speaking V1 Written word (Broca’s Area) perception Word choice (VWFA) Sequencing Grammar Articulation  CONDUCTION APHASIA Characterized by an inability to repeat the exact words you hear. Other than that, speech is meaningful and fluid. Language comprehension and expression are generally fine. When asked to repeat the word ‘house’, the person may say “home”. When asked to repeat a nonsense word like ‘blaynge’, the person will be unable to do it. They will just say I didn’t hear you.  CONDUCTION APHASIA Involves damage to the arcuate fasciculus: axons that interconnect Wernicke’s area and Broca’s area Wernicke’s Area Conduction aphasia is characterized by inability to repeat words that are heard, particularly when comprehension and speaking abilities are intact. It is caused by damage around the arcuate fasciculus, a bundle of axons that interconnects Wernicke's area and Broca's area. CONDUCTION APHASIA  WERNICKE'S AREA Wernicke’s area is where sounds are recognized as spoken words. It is part of auditory association cortex in the left temporal lobe. – Being able to hear is one thing (primary auditory cortex); – Recognizing sounds as words is another thing (Wernicke’s Area); – Word comprehension—understanding word meaning—is yet another thing (Posterior Language Area) (Note that Posterior Language Area overlaps with Wernicke’s area)  PURE WORD DEAFNESS Is the result of damage to a small part of Wernicke’s area Pure word deafness is a disorder of auditory word recognition, an inability to comprehend or repeat spoken words. “I can hear you, but I don’t recognize the words you are saying. I even have trouble repeating what you say.” It is caused by damage in or around Wernicke's area.  PURE WORD DEAFNESS Is the result of damage to a small part of Wernicke’s area People with Pure Word Deafness can Hear just fine. Interpret non-speech sounds (doorbell, phone, barking). Read and write. Read lips. Speak intelligently, but they can’t recognize the words they are saying by listening to themselves. Over time their speech becomes a bit awkward, like when a deaf person speaks.  WERNICKE'S APHASIA Results from damage around Wernicke’s area and the Posterior language area. It is a combination of transcortical sensory aphasia and pure word deafness.  WERNICKE'S APHASIA The defining feature of both Wernicke's aphasia and transcortical sensory aphasia is poor language comprehension. People with these conditions speak fluently, but what they say is largely meaningless and filled with function words: a, the, in, about (as opposed to content words such as nouns and verbs). Their speech seems natural and is filled with intonation and emphasis (prosody). Words seem to come easy to them, but what they say is often meaningless. They are typically not fully aware of the problem and are unbothered by it. These disorders are referred to as receptive aphasias (an inability to understand words that are heard, read, or signed) as well as fluent aphasias (the ability to speak fluently without conveying much meaning). The key difference between Wernicke's aphasia and transcortical sensory aphasia is that people with TSA often repeat what is said to them, so they clearly recognize spoken words, while people with Wernicke's aphasia often cannot repeat what is said to them. Spoken word recognition and word comprehension abilities are interwoven in and around Wernicke’s area. It is often not possible to differentiate these components by looking at a brain scan. RECEPTIVE, FLUENT APHASIA (WERNICKE’S APHASIA)  DISORDERS OF READING Written word Speaking perception (Broca’s Area) (Visual Word- Form Area) VWFA  PURE ALEXIA Damage to the visual word-form area (VWFA) in visual association cortex disrupts the ability to perceive written words. The visual word-form area is in the fusiform gyrus of the left hemisphere, whereas face perception is more dominant in the fusiform gyrus of the right hemisphere. People with damage to the VWFA cannot read (pure alexia or pure word blindness), as they cannot recognize written words. They can typically write just fine, but they just cannot read what they write.  READING Both of these people damaged V1 in their left cerebral hemisphere, but their fusiform gyrus in their left hemisphere (VWFA) is still intact. Posterior language area / The person on the left can read in left peripheral vision. The person on the right cannot read due to additional damage in the corpus callosum.  READING Dyslexia means “faulty reading”. People with dyslexia have difficulty reading. Reading Reading involves at least two different processes: direct recognition of whole words and sounding out words letter by letter Whole-word Recognition of whole words is called “sight reading” reading Phonetic Recognizing words by sounding out strings of letters reading is called “sound reading”  SIGHT READING Like the fusiform face area, which is critical for perceiving faces as a whole and differentiating them, the visual word form area (VWFA) is critical for perceiving written words as a whole and differentiating them. How quickly can you tell the difference between these two words? Surface dyslexia: An inability to recognize whole words, while retaining the ability to read phonetically. Irregularly spelled words are difficult for these people to read, because sounding them out doesn’t work: Pair, pear, pare,…. Sew, pint, yacht,…. Phonological dyslexia: Reading disorder in which a person can read familiar words but has difficulty reading unfamiliar words or non-words. Blint, trisk, juff,…. Kanji vs Kana Japanese symbols  READING The neural basis of dyslexia is not well known. The problem is largely hereditary. Developmental dyslexia is mostly a type of phonological dyslexia. People with developmental dyslexia have great difficulty learning to read and some never become fluent readers, even though they are otherwise intelligent. They also have trouble with grammar and spelling and have a hard time distinguishing the order of sound sequences.  SELECTIVE DISORDERS OF READING Some stroke patients have very specific deficits in their ability to extract meaning from written words even though they can read out loud. This symptom is called Direct Dyslexia. It is typically seen with larger deficits, like transcortical sensory aphasia where there is limited language comprehension. Writing Direct Dyslexia Talk out loud Visual (Broca’s Area) (written) word perception (reading – VWFA)  READING The most important cues for object recognition (which is the primary task of the visual system) are those that remain relatively constant when objects are viewed from different angles The most reliable cues are where lines meet at vertices, forming junctions with particular shapes, such as L, T, and X SPEECH PRODUCTION: BROCA’S AREA  SPEECH PRODUCTION Damage to Broca’s area in the left inferior frontal lobe makes it difficult for patients to express themselves verbally. This deficit is known as Broca's aphasia and it is characterized by slow, laborious, nonfluent speech Patients have something to say, but they have trouble saying it. They are fully aware of their condition and are very frustrated by it. BROCA’S APHASIA  BROCA’S APHASIA Broca’s aphasia encompasses three semi-distinct issues articulation problems agrammatism anomia Articulation Movement of tongue, lips, jaw, and other speech organs to make speech sounds. Articulation problems might make it hard for someone to hear the words you are saying. Or it could cause a sequencing problem: lipstick  lickstip.  AGRAMMATISM Agrammatism Difficulty comprehending or using grammatical devices, such as verb endings (-ed) and word order (e.g., man bit dog). People with agrammatism typically do not derive meaning from the sequence of words or the grammar of sentences. They almost exclusively use content words (nouns, adjectives, verbs, etc.) without any function words (the, on, about, etc.). People with Broca's aphasia comprehend speech much better than they can produce it, but there usually are some comprehension deficits. SPEECH PRODUCTION AND COMPREHENSION Content word Noun, verb, adjective, or adverb that conveys meaning. People with Broca’s aphasia have trouble coming up with content words, but that is how they communicate. They rarely use function words. Function word Preposition, article, and other words that convey little meaning but are important for the grammatical structure of sentences (a, the, in).  ANOMIC APHASIA Anomia Difficulty finding the appropriate word to describe an object, action, or attribute. This is a common symptom of all aphasias, especially Broca’s aphasia. Anomic A relatively mild aphasia in which people have a hard time aphasia thinking of the words they want to say. They understand spoken words and speak just fine, but they describe things in roundabout ways (circumlocution). Circumlocution Strategy by which people with anomia find alternative ways to say something when they are unable to think of most appropriate word ANOMIC APHASIA