Lateralization Flashcards
What’s lateralization and why is it important.
Key Findings
• Lateralization refers to the functional specialization of the left and right hemispheres of the brain.
• Although both hemispheres work together, certain functions are dominantly processed in one hemisphere.
• Left Hemisphere Specialization:
• Language processing (Broca’s & Wernicke’s areas).
• Logical reasoning & analytical thinking.
• Fine motor control (e.g., right-hand movement in most right-handed individuals).
• Right Hemisphere Specialization:
• Spatial processing & face recognition.
• Emotional processing & prosody (tone of voice).
• Holistic thinking & pattern recognition.
• Importance of Lateralization:
• Allows the brain to divide tasks efficiently, improving processing speed and cognitive abilities.
• Damage to one hemisphere can lead to specific deficits (e.g., aphasia with left hemisphere damage).
Key Takeaway
• Lateralization allows the brain to specialize in different cognitive functions, with the left hemisphere dominant for language and logic, and the right hemisphere dominant for spatial abilities, emotion, and holistic thinking.
What are split-brain individuals, and what do they reveal about brain lateralization?
Key Findings
• Split-brain individuals are people who have had their corpus callosum surgically severed, typically as a treatment for severe epilepsy.
• This procedure prevents communication between the left and right hemispheres, leading to distinct behaviors when stimuli are presented to only one hemisphere.
• Key Observations from Split-Brain Studies:
• Left hemisphere (dominant for language):
• Can verbalize what it sees (when stimuli are presented to the right visual field).
• Right hemisphere (dominant for spatial processing & nonverbal communication):
• Cannot verbalize what it sees (when stimuli are presented to the left visual field).
• Can process spatial tasks and recognize objects but struggles to name them.
• Example Experiment:
• If an object is presented to the left visual field (right hemisphere), the person cannot name it but can pick it up with the left hand.
Key Takeaway
• Split-brain studies confirm brain lateralization, showing that the left hemisphere specializes in language while the right hemisphere processes spatial and nonverbal tasks.
• The corpus callosum plays a crucial role in integrating information between hemispheres.
What do split-brain studies reveal about hemispheric specialization?
Key Findings
• Left Hemisphere (LH) Specialization:
• Dominant for language processing (speech production and comprehension).
• Can verbalize stimuli presented in the right visual field (processed by the left hemisphere).
• Right Hemisphere (RH) Specialization:
• Better at spatial tasks and recognizing faces.
• Cannot verbalize what it sees but can process and respond nonverbally.
• If an object is presented in the left visual field (processed by RH), the individual cannot name it but can pick it up with the left hand.
• Key Experiment (Visual Stimuli & Responses in Split-Brain Patients):
• A word or object is flashed to one visual field:
• Right visual field (LH processing) → Patient can say the word aloud.
• Left visual field (RH processing) → Patient cannot verbalize the word but can draw or pick it up with the left hand.
• Implications:
• Confirms lateralization: LH is specialized for language, while RH handles spatial and nonverbal processing.
• Corpus callosum integrates hemispheric functions; its absence results in independent processing in each hemisphere.
Key Takeaway
• Split-brain studies demonstrate that the left hemisphere is dominant for language, while the right hemisphere excels in spatial and nonverbal tasks.
• Without the corpus callosum, the hemispheres act independently, revealing how each side of the brain contributes to cognition.
What do split-brain studies reveal about dual consciousness and confabulation?
Key Findings
• Dual Consciousness:
• Each hemisphere processes information independently and can complete tasks correctly on its own.
• Right hemisphere lacks language, so it cannot explain its choices verbally.
• Key Experiment (Shovel & Chicken Task):
• Right visual field (LH processing) → Sees chicken claw, selects chicken.
• Left visual field (RH processing) → Sees snow scene, selects shovel.
• When asked why they picked the shovel, the left hemisphere, which didn’t see the snow, confabulates, saying “The shovel is for cleaning the chicken coop.”
• Implications:
• Each hemisphere functions independently, supporting dual consciousness.
• The left hemisphere fills in missing information with logical but false explanations (confabulation).
Key Takeaway
• Split-brain patients demonstrate dual consciousness, where the right hemisphere makes correct nonverbal choices but cannot explain them, while the left hemisphere confabulates to maintain a coherent narrative.
What is callosal agenesis, and how does it differ from surgical split-brain patients?
Key Findings
• Callosal Agenesis:
• Occurs in 1 in 4000 people, where individuals are born partially or completely lacking a corpus callosum (hemisphere not connected).
• Unlike surgically split-brain patients, they do not exhibit severe neuropsychological deficits.
• Neural Compensation:
• During development, the nervous system adapts by strengthening alternative interhemispheric connections.
• Other brain pathways (e.g., anterior commissure) may help compensate for the lack of direct corpus callosum communication.
• Implications:
• The brain has a remarkable ability to reorganize itself when disruptions occur early in development.
• Highlights the difference between developmental vs. acquired brain changes—early deficits allow for adaptation, while sudden lesions (like in split-brain surgery) do not.
Key Takeaway
• People with callosal agenesis often lack the cognitive impairments seen in split-brain patients because the developing brain compensates by strengthening alternative connections between hemispheres.
What is dichotic presentation, and why do some people show an ear advantage?
Dichotic Presentation:
• A method where different auditory stimuli are played simultaneously into each ear.
• Used to study hemispheric dominance in auditory processing.
• Right Ear Advantage (REA):
• Most people show better recognition of verbal stimuli (e.g., words, numbers) in the right ear.
• This happens because the right ear projects directly to the left hemisphere, which is dominant for language processing.
• Left Ear Advantage (LEA):
• Some individuals may have a left ear advantage for nonverbal sounds (e.g., music, environmental sounds).
• The left ear projects to the right hemisphere, which specializes in spatial and emotional auditory processing.
• Implications:
• Ear advantage reflects hemispheric specialization, with the right ear favoring language (left hemisphere) and the left ear favoring nonverbal sounds (right hemisphere).
Key Takeaway
• Dichotic listening tasks reveal hemispheric dominance, with a typical right ear advantage for language and a left ear advantage for nonverbal sounds.
What is the tachistoscope test, and what does it reveal about hemispheric dominance?
Key Findings
• Planum Temporale:
• A cortical area in the superior temporal lobe, adjacent to the primary auditory cortex.
• Larger in the left hemisphere in most individuals.
• Asymmetry and Language:
• Leftward asymmetry is present before birth, supporting the idea that language lateralization is innate rather than purely experience-based.
• The larger left planum temporale is linked to language dominance in the left hemisphere.
• Variation in Asymmetry:
• Most right-handed people have a larger left planum temporale.
• Some left-handed people show more symmetrical or reversed asymmetry, though many still have a leftward bias.
Perfect Pitch and Planum Temporale:
• Musicians with perfect pitch tend to have an even more pronounced leftward asymmetry in the planum temporale.
• Suggests a connection between auditory processing specialization and structural differences in the brain.
• Implications: • Planum temporale asymmetry is an early structural marker of language lateralization, supporting the biological basis of hemispheric dominance.
Key Takeaway
• The planum temporale is typically larger in the left hemisphere, reinforcing the left hemisphere’s role in language processing, with this asymmetry evident before birth.
What is the planum temporale, and why is it important?
Key Findings
• Planum Temporale:
• A cortical area in the superior temporal lobe, adjacent to the primary auditory cortex.
• Larger in the left hemisphere in most individuals.
• Asymmetry and Language:
• Leftward asymmetry is present before birth, supporting the idea that language lateralization is innate rather than purely experience-based.
• The larger left planum temporale is linked to language dominance in the left hemisphere.
• Variation in Asymmetry:
• Most right-handed people have a larger left planum temporale.
• Some left-handed people show more symmetrical or reversed asymmetry, though many still have a leftward bias.
Perfect Pitch and Planum Temporale:
• Musicians with perfect pitch tend to have an even more pronounced leftward asymmetry in the planum temporale. Music activates the right hemisphere more than the left, and musical perception is damaged when right hemisphere damaged.
• Suggests a connection between auditory processing specialization and structural differences in the brain.
• Implications: • Planum temporale asymmetry is an early structural marker of language lateralization, supporting the biological basis of hemispheric dominance.
Key Takeaway
• The planum temporale is typically larger in the left hemisphere, reinforcing the left hemisphere’s role in language processing, with this asymmetry evident before birth.
What is the Wada test, and what does it reveal about brain lateralization?
Key Findings
• Wada Test:
• A procedure used to determine which hemisphere is dominant for language.
• Involves injecting a fast-acting anesthetic (sodium amobarbital) into one carotid artery, temporarily inactivating one hemisphere.
• Procedure & Observations:
• If the left hemisphere is anesthetized (in most people):
• Speech production is impaired or lost, confirming left hemisphere dominance for language.
• If the right hemisphere is anesthetized:
• Speech is typically unaffected, unless the person has right hemisphere language dominance (rare).
• Uses of the Wada Test:
• Pre-surgical evaluation for epilepsy patients before brain surgery.
• Helps determine language dominance and memory function to avoid damaging critical areas.
• Implications:
• Confirms that the left hemisphere is dominant for language in most people.
Key Takeaway
• The Wada test temporarily disables one hemisphere to assess language dominance, confirming left hemisphere specialization in most individuals.
What is prosopagnosia, and what causes it?
Key Findings
• Definition:
• Prosopagnosia, or face blindness, is the inability to recognize familiar faces, despite normal vision and intelligence.
• Causes:
• Acquired Prosopagnosia:
• Results from brain damage, often due to stroke, trauma, or neurodegeneration.
• Typically linked to lesions in the fusiform face area (FFA) of the right temporal lobe.
• Congenital (Developmental) Prosopagnosia:
• Present from birth with no obvious brain damage.
• May result from abnormal development of face-processing networks.
• Symptoms:
• Difficulty recognizing familiar faces, even close friends or family.
• May rely on voice, clothing, or other cues to identify people.
• In severe cases, individuals may fail to recognize their own face in a mirror.
• Implications:
• Prosopagnosia highlights the specialized role of the fusiform gyrus in facial recognition.
Key Takeaway
• Prosopagnosia is a disorder affecting face recognition, usually due to damage in the fusiform face area (FFA), demonstrating the brain’s specialized system for processing faces.
What does FMRI reveal about prospagnosia and the fusiform face area (FFA)?
Key Findings
• Study Overview:
• Researchers examined face-selective activation in the fusiform gyrus (FFA) using fMRI.
• Patients with prosopagnosia showed weaker or absent FFA activation compared to control participants.
• Key Results:
• Healthy individuals:
• Strong activation in the right fusiform gyrus (FFA) when viewing faces.
• Prosopagnosia patients:
• Significantly reduced or absent FFA activation, correlating with their inability to recognize faces.
• Implications:
• Confirms that the FFA is crucial for face recognition.
• Damage or dysfunction in the FFA leads to prosopagnosia, reinforcing the specialized role of this brain region in face processing.
Key Takeaway
• Prosopagnosia results from impaired fusiform face area (FFA) function, as demonstrated by fMRI studies showing weaker activation in affected individuals.
What is congenital prosopagnosia, and what does the “Greenies” study reveal about it?
Key Findings
• Congenital Prosopagnosia (Developmental Prosopagnosia):
• A lifelong inability to recognize faces, despite normal vision and no history of brain injury.
• May result from abnormal development or weaker connectivity in the fusiform face area (FFA) and its network.
• Individuals may rely on other cues (e.g., voice, hairstyle) to recognize people.
• The “Greenies” Study (Face Learning in Prosopagnosia):
• Researchers created a fictional alien species (“Greenies”), which had two genders and five families, requiring participants to learn to recognize them.
• Key Findings:
• Individuals with congenital prosopagnosia struggled to learn and distinguish Greenies, similar to their difficulty recognizing human faces.
• They performed normally on non-face object recognition tasks, suggesting a face-specific deficit rather than a general visual impairment.
Key Takeaway
• Congenital prosopagnosia is a lifelong impairment in face recognition, likely due to atypical FFA development. The “Greenies” study confirms that individuals with this condition struggle with face learning, reinforcing that their deficit is specific to facial processing, not general vision.
What are super-recognizers, and what makes them different from the general population?
Key Findings
• Definition:
• Super-recognizers are individuals with exceptional face recognition ability, far above the average person.
• They can effortlessly remember and identify faces, even after brief encounters or long time gaps.
• Key Characteristics:
• Can recognize faces even with changes in age, hairstyle, or lighting.
• Perform extremely well on face recognition tests, such as identifying people from low-quality security footage.
• May notice subtle differences between similar-looking individuals that others miss.
• Neural Basis:
• fMRI studies suggest super-recognizers have stronger activation in the fusiform face area (FFA) compared to average individuals.
• Implications:
• Demonstrates that face recognition ability exists on a spectrum, with prosopagnosia on one end and super-recognizers on the other.
• Some law enforcement agencies recruit super-recognizers for surveillance and security work.
Key Takeaway
• Super-recognizers have exceptional face recognition skills, likely due to enhanced FFA function, highlighting the variability in human facial processing abilities.
What do studies comparing self and celebrity face recognition reveal?
Key Findings
• Study Overview:
• Compared recognition of one’s own face vs. celebrity faces using fMRI.
• Measured brain activation in response to self-faces, familiar faces (celebrities), and unfamiliar faces.
• Key Results:
• Right Hemisphere Dominance for Self-Recognition:
• Greater activation in the right hemisphere when viewing one’s own face, particularly in the right fusiform gyrus and right frontal regions.
• Left Hemisphere Involvement in Familiar Face Recognition:
• Celebrity face recognition showed more balanced activation across both hemispheres.
• Self-Face Recognition is More Robust:
• People tend to recognize their own face faster and more accurately than celebrity faces.
• Key Takeaway
• Self-face recognition relies more on the right hemisphere, while celebrity face recognition involves both hemispheres, suggesting the brain processes personal identity and familiar faces differently.
What are the fundamental components of language, and what do they mean?
Key Findings
1. Phonemes (音素):
• The smallest unit of sound in a language that distinguishes meaning.
• Example: /p/ and /b/ in “pat” vs. “bat” change the word’s meaning.
2. Morphemes (语素):
• The smallest meaningful unit of language.
• Example: “un-”, “happy”, and ”-ness” in “unhappiness” each contribute to the word’s meaning.
3. Syntax (句法):
• The rules governing sentence structure and word order.
• Example: In English, “The cat chased the dog” is different from “The dog chased the cat”.
4. Semantics (语义学):
• The meaning of words and sentences.
• Example: “Colorless green ideas sleep furiously” is syntactically correct but lacks clear meaning.
5. Pragmatics (语用学):
• The social rules of language use in context.
• Example: “Could you pass the salt?” is a request, not a literal yes/no question.
Key Takeaway
• Language is structured into different levels—phonemes (sounds), morphemes (meaningful units), syntax (structure), semantics (meaning), and pragmatics (social context)—all working together for communication.
What is aphasia, what are its symptoms, and what causes it?
Key Findings
• Aphasia is a language disorder caused by brain damage, affecting speech production, comprehension, reading, or writing.
• 90-95% of aphasias result from left-hemisphere damage, typically due to stroke, brain injury, tumors, or neurodegenerative diseases.
• Common Symptoms of Aphasia:
• Nonfluent speech – Difficulty forming words and sentences (e.g., Broca’s aphasia).
• Fluent but nonsensical speech – Words flow but lack meaning (e.g., Wernicke’s aphasia).
• Impaired comprehension – Difficulty understanding spoken or written language.
• Word-finding difficulties (Anomia) – Struggling to recall words.
• Repetition deficits – Difficulty repeating phrases, especially in conduction aphasia.
Key Takeaway
• Aphasia is a language disorder, typically caused by left-hemisphere damage (90-95% of cases), leading to deficits in speech production, comprehension, reading, and writing.
What additional symptoms can appear in aphasia?
Key Findings
• Aphasia can also involve other language-related deficits, depending on the brain areas affected.
• Common Additional Symptoms:
• Agraphia (书写障碍) → Impaired ability to write, even when motor skills are intact.
• Alexia (失读症) → Impaired reading ability, often co-occurring with aphasia.
• Apraxia (失用症) → • Speech Apraxia → Difficulty with motor planning for speech, leading to slow, effortful articulation. • Limb Apraxia → Difficulty performing purposeful movements, despite normal strength and coordination. • **Damage to the angular gyrus is often associated with agraphia and alexia.
Key Takeaway
• Aphasia is often accompanied by agraphia (writing impairment), alexia (reading impairment), and in some cases, apraxia (motor planning difficulties), depending on the extent of brain damage.
What is the difference between fluent and nonfluent aphasia?
Key Findings
• Fluent Aphasia (Wernicke’s Aphasia):
• Speech is fluent but lacks meaning (“word salad”).
• Poor comprehension of both spoken and written language.
• Unaware of their deficits and often not frustrated by their speech.
• Example: Speaking in long, grammatically correct sentences, but with nonsensical or irrelevant content.
• Nonfluent Aphasia (Broca’s Aphasia): • Speech is slow, effortful, and grammatically impaired. • Good comprehension but struggles to express thoughts verbally. • Aware of their impairment and often frustrated by their difficulty in speaking. • Example: “Want… coffee… now” instead of “I want some coffee now.”
Key Takeaway
• Fluent aphasia (Wernicke’s) allows speech but impairs comprehension, while nonfluent aphasia (Broca’s) preserves comprehension but makes speech effortful and broken.
What brain regions are affected in fluent and nonfluent aphasia?
Key Findings
• Broca’s Aphasia (Nonfluent Aphasia):
• Location: Broca’s area (left inferior frontal gyrus).
• Function: Responsible for speech production and articulation.
• Damage Effects:
• Impaired speech production (slow, effortful, nonfluent).
• Comprehension remains intact.
• Patients are aware of their deficits and sometime frustrated.
• Wernicke’s Aphasia (Fluent Aphasia):
• Location: Wernicke’s area (left superior temporal gyrus).
• Function: Critical for language comprehension.
• Damage Effects:
• Fluent but nonsensical speech (word salad).
• Severe comprehension deficits (both spoken and written language).
• Patients are unaware of their impairment and not frustrated.
Key Takeaway
• Broca’s aphasia is caused by damage to Broca’s area (left frontal lobe) and affects speech production, while Wernicke’s aphasia results from damage to Wernicke’s area (left temporal lobe) and impairs language comprehension.
What do dichotic listening, split-brain studies, Broca’s aphasia, and somatosensory involvement tell us about language processing?
Key Findings:
• Lateralization & Dichotic Listening
• Right ear inputs (processed by the left hemisphere) are recognized faster, supporting left hemisphere dominance for language.
• Split-Brain & Split-Screen Tasks
• Left visual field (right hemisphere) → Cannot verbalize but can identify objects with the left hand.
• Right visual field (left hemisphere) → Can name and describe objects, confirming left hemisphere’s role in language production.
• Broca’s Aphasia
• Damage to Broca’s area (left frontal lobe) causes nonfluent, effortful speech but spares comprehension.
• Patients are often aware of their deficits, leading to frustration.
• Somatosensory Language Involvement
• The somatosensory system may support speech perception by linking mouth/tongue movements to sounds.
• Suggests that language processing is not purely abstract but involves sensorimotor integration.
Key Takeaway:
• Language is strongly lateralized to the left hemisphere, as shown in dichotic listening and split-brain studies. Broca’s aphasia highlights the role of the frontal lobe in speech production, while somatosensory areas may support speech perception and articulation.
How do Broca’s and Wernicke’s aphasia differ in terms of brain region, speech fluency, and comprehension?
Key Findings:
• Broca’s Aphasia
• Region: Broca’s area in the left premotor/frontal region.
• Speech: Nonfluent, slow, effortful speech with poor grammar.
• Comprehension: Largely preserved.
• Other: Patients are often aware of their difficulty.
• Wernicke’s Aphasia
• Region: Wernicke’s area in the left superior temporal gyrus.
• Speech: Fluent but nonsensical (word salad).
• Comprehension: Severely impaired.
• Other: Patients are often unaware of their impairment.
Key Takeaway:
• Broca’s aphasia results in nonfluent speech with preserved comprehension, while Wernicke’s aphasia produces fluent but meaningless speech with poor comprehension, reflecting damage to different language areas.
What is fluent aphasia, what does word deafness indicate, and how are anomia and the angular gyrus involved?
Key Findings:
• Fluent Aphasia (Wernicke’s Aphasia)
• Speech: Fluent but lacks meaning (word salad).
• Comprehension: Impaired, especially for spoken language.
• Cause: Damage to Wernicke’s area in the left superior temporal gyrus.
• Word Deafness
• Inability to comprehend spoken words, despite normal hearing and intact speaking, reading, and writing.
• Indicates damage to the superior temporal lobe, often bilateral or deep in the left hemisphere.
• Suggests that hearing words and understanding them rely on distinct neural mechanisms.
• Anomia (Word-Finding Difficulty)
• A common symptom in many types of aphasia, including Wernicke’s aphasia.
• Patients struggle to recall words, often using circumlocutions (e.g., “the thing you sit on” instead of “chair”).
• Angular Gyrus and Language Processing
• Located in the parietal lobe, crucial for language-related functions, including reading and writing.
• Damage can cause alexia (reading impairment) and agraphia (writing impairment).
• Plays a role in word retrieval, contributing to anomia when damaged.
Key Takeaway:
• Fluent aphasia disrupts comprehension despite smooth speech, word deafness reflects auditory-language processing deficits, and damage to the angular gyrus can impair reading, writing, and word retrieval (anomia).
Global Aphasia – Meaning, Symptoms, and Causes
Key Findings:
• Definition:
• Global aphasia is the most severe form of aphasia, affecting both speech production and comprehension.
• Patients have very limited communication ability, often only producing a few words or sounds.
• Symptoms:
• Nonfluent speech – Severe difficulty forming words or sentences.
• Severely impaired comprehension – Cannot understand spoken or written language.
• Difficulty repeating words – Unable to echo spoken phrases.
• Cause:
• Extensive damage to the left hemisphere, affecting both Broca’s area (speech production) and Wernicke’s area (comprehension).
• Often caused by a large stroke in the middle cerebral artery (MCA) territory, leading to widespread language deficits.
Key Takeaway:
• Global aphasia results from extensive left-hemisphere damage, causing severe impairments in speech production, comprehension, and repetition, making communication extremely limited.
What are the key models of the brain’s language circuitry, and what does the connectionist model of aphasia propose?
Key Findings:
• Classical Model (Wernicke-Geschwind Model)
• Broca’s area: Controls speech production.
• Wernicke’s area: Responsible for language comprehension.
• Angular gyrus: Involved in reading and writing.
• Arcuate fasciculus: A bundle of axons connecting Wernicke’s and Broca’s areas.
• Critical for repetition of heard speech.
• Damage leads to conduction aphasia: fluent speech and good comprehension, but impaired repetition.
• Connectionist Model of Aphasia
• Views the brain’s language system as a network of interconnected regions, rather than isolated centers.
• Emphasizes the importance of connections (e.g., arcuate fasciculus) for integrating comprehension and production.
• Explains how different types of aphasia result from disruption in specific nodes or connections in the language network.
Key Takeaway:
• The brain’s language circuitry involves Broca’s and Wernicke’s areas, connected by the arcuate fasciculus. The connectionist model views language as a network, where damage to regions or connections leads to different types of aphasia.
