Speech and Language Fundamentals

Speech and Language

• Speech is a means of transferring ideas from one individual to another through the vibration of molecules in the air.
• Language is a social engagement that involves deducting what others know or believe.
• Animals may have language, as demonstrated by Washoe, Kanzi, and Golden seabrights.

Speech Production vs Comprehension

• Speech production involves the production of spoken words, while comprehension involves perceiving and understanding spoken words.

Spoken Word Recognition

• We match the acoustic form of spoken words to a stored set of words in our vocabulary, known as the phonological lexicon.
• The process of matching is called lexical access, and it involves competition between similar sounding words.
• The access units are debated, but the consensus is that speech recognition involves a cohort of words that are initially considered as candidates, with words getting eliminated as more evidence accumulates.

Cohort Model

• In lexical access, many spoken words are initially considered as candidates, but words get eliminated as more evidence accumulates.
• The uniqueness point is reached when the acoustic input unambiguously corresponds to only one known word.
• The time taken to recognize a word depends on how early or late the uniqueness point occurs.
• Linguistic factors that influence recognition include frequency of a word, imageability of a word, and contextual information.

Words in Context

• The cohort model explains how a single word is recognized, but words are normally spoken in the context of a discourse.
• EEG studies show that out-of-context words induce a N400 response, while grammatical errors induce a P600 response.

Aphasia

• Aphasia is a disorder of language due to brain damage on the left hemisphere, causing problems in speech perception, speech production, and writing.

Language Specialization

• Broca's area is located in the frontal lobe and is responsible for speech production, with damage causing Broca's aphasia.
• Wernicke's area is located in the temporal lobe and is responsible for language comprehension, with damage causing Wernicke's aphasia.
• Broca's aphasia patients have trouble with fluent speech, while Wernicke's aphasia patients have trouble with comprehending language.

Sentence Comprehension

• Words have meaning (semantics) and syntactic roles (grammatical classes such as nouns and verbs).
• Syntax enables the listener to figure out who is doing what to whom.
• Broca's aphasia is related to agrammatism, or the loss of grammar.

Broca's Area

• Broca's area has two functional sub-divisions: the posterior division (BA44) related to syntactic complexity, and the anterior division (BA45) related to working memory and meaning.
• Syntax and semantics are separable but not completely independent, and Broca's area can be viewed as an integration site.

Retrieval of Spoken Words

• When producing speech, three types of information need to be retrieved: lexicalization (the selection of a word based on meaning), grammatical properties, and form of the word (syllables, phonemes).

Speech Errors

• Speech errors include Freudian slips, malapropisms, spoonerisms, and tip-of-the-tongue phenomenon.
• Anomia is a word-finding difficulty due to brain damage, resulting in a constant state of tip-of-the-tongue phenomenon.
• Proper name anomia is a severe difficulty in retrieving proper names.

Articulation

• Articulation is the final stage of speech, associated with the basal ganglia and insula.
• Damage to the insula results in apraxia for speech, or difficulties in shaping the vocal tract.
• Damage to the basal ganglia results in dysarthria, or impaired muscular contractions.

Literacy

• Literacy is the ability to read and write, enabling communication without face-to-face contact.
• It is an expert system derived from a core set of other skills such as visual recognition, manipulation of sounds, learning, and memory.
• Visual word recognition involves processing letter strings as a whole, rather than one by one.
• The visual lexicon is a storage for how words are written.
• The word superiority effect states that it is easier to detect a letter in the context of a word or nonsense letter string than in a random letter string or in isolation.
• The visual word form area is a dedicated cognitive mechanism for visual lexicon, located in the left mid-fusiform gyrus, and also responds to visual objects and Braille reading.

Acquired Reading Deficiencies

• Central dyslexia: disruption of reading arising after computation of a visual word form.
  • Surface dyslexia: reading nonwords and regularly spelled words better than irregularly spelled words.
  • Phonological dyslexia: reading real words better than nonwords.
  • Deep dyslexia: real word reading prone to semantic errors.
• Peripheral dyslexia: disruption of reading arising up to the level of computation of a visual word form.
  • Pure alexia: an acquired difficulty in reading words that leads to letter-by-letter reading.

fMRI Studies

• Multiple areas involved in literacy, predominantly left-lateralized.
  • Inferior frontal lobe (Broca's area).
  • Inferior parietal lobe (Wernicke's and angular gyrus – verbal working memory).
  • Anterior and mid-temporal lobes (semantic memory).
• Reading uses similar brain regions across different languages, albeit to varying degrees.

Spelling and Writing

• Dysgraphia: difficulties in spelling, with similar deficiencies as central dyslexia.
  • Deep dysgraphia: real word spelling prone to semantic errors.
• Dysgraphia is generally multimodal, with patients producing similar errors in writing, typing, or oral spelling.
• Evidence suggests separate written versus oral letter name output codes in spelling, indicating involvement of motor codes in writing.

Numeracy

Universal Numeracy

• Numeracy is not limited to math; humans and other species have numerical abilities that enable estimation of quantity and basic calculations.
• Infants, unschooled, cavemen, and non-human animals all possess numerical abilities.
• Fundamental sense of numeracy is universal, except for dyscalculia.

Numbers

• Non-symbolic number processing is universal.
• Ability to perform tasks becomes harder with increasing sets, even if the ratio remains the same.
• We can subitize (enumerate an exact quantity of objects without counting them) up to 4 items.
• Numbers above 4 can only be processed approximately rather than exactly in the absence of language.

Processing Symbolic Numbers

• Distance effect: faster decision-making when the distance between two numbers is large.
• Size effect: easier judgment of larger numbers when they are small.

Neural Subtrates

• Number meaning: not only countable quantities but also continuous and uncountable quantities are processed by the number system.

Numbers and Space

• SNARC effect (Spatial-Numerical Association of Response Codes): cultural variations and other SNARC-like effects.

Triple Code Model

• 1. Abstract (semantic) magnitude.
• 2. Verbal store of numbers and operations.
• 3. Visual representation for numerals (digits) and workbench for certain calculations.

Executive Functions

• Executive functions: complex processes that optimize performance in situations requiring multiple cognitive processes
• Not tied to a specific domain (e.g., memory, language, perception) but have a meta-cognitive, supervisory, or controlling role
• Related to prefrontal cortex (PFC)

Problem-Solving

• Problem-solving involves generating a solution with a given endpoint (goal) and optional starting point (objects)
• Tests: Tower of London, FAS test, Cognitive Estimates Test
• PFC lesions often lead to poor problem-solving

Overcoming Habitual Responses

• Inhibition: reducing the likelihood of a particular thought/action
• Related to medial PFC, specifically anterior cingulate cortex (ACC) and pre-SMA
• Example: Stroop task (name the color of the ink and ignore reading the color name)

Overcoming Potent Responses

• Inhibition: reducing the likelihood of a particular thought/action
• Related to medial PFC, specifically ACC and pre-SMA
• Example: Go/No-Go task (respond to frequent stimulus, but withhold response to another stimulus)

Task Switching

• Requires PFC activation and discarding a previous schema and establishing a new one
• PFC damage leads to perseveration (failure to shift)
• Example: Wisconsin Card Sorting Test (adjust responses to new rule)
• Switch cost: slowing of response time due to discarding a previous schema and setting up a new one

Multi-Tasking

• Carrying out several tasks in succession, requiring task switching and maintaining future goals
• Patients with anterior prefrontal cortex lesions may be impaired at multi-tasking
• Example: Six Element Test (patients with prefrontal lesions may fail to switch tasks)

Decision Making

• Decisions are not solely based on rationality, even without brain damage
• Framing or social justice perception can affect decisions
• Involves ACC and OFC

Somatic Marker Hypothesis

• Somatic markers link previous situations stored in the cortex and the "feeling" of those situations stored in emotional and bodily response regions
• Located in vmPFC, influencing ongoing behavior in situations where feelings are critical

Iowa Gambling Test and Delay Discounting

• Iowa Gambling Test: a decision-making task involving risks and rewards
• Delay discounting: choosing between current and future rewards
• OFC lesions lead to planning failure and impulsive behavior

Multiple Demand Network

• Lateral PFC, ACC, and intraparietal sulcus are involved in cognitive control
• Not separate subdivisions, but a single network
• Fluid vs crystallized intelligence

Hemispheric Differences

• Not found in other primates; humans have more lateralized brain function
• Left lateral PFC: specialized in problem-solving, right lateral PFC: task monitoring

Anterior Cingulate Cortex (ACC)

• Considered part of limbic system
• Functionally two different regions: dorsal ACC (cognitive division) and rostral ACC (affective division)
• Involved in error detection and recalibration of task performance

Emotions

• Emotions are states associated with stimuli that are rewarding or punishing, guiding behavior and social interactions.
• Emotions tag stimuli with emotional states, even if they are not naturally affective.
• Emotions are critical for guiding social behavior, including mentalizing and mirroring others' emotions and mental states.

Theories of Emotion

• Darwin's theory: human emotions possess continuity with their animal counterparts, with conserved expressions across species.
• James-Lange Theory: self-perception of bodily changes produces emotional experience, but contemporary views suggest bodily experiences modify emotional experiences.
• Cannon-Bard Theory: bodily responses occur after the emotion itself, with emotions coming before expression.

Papez Circuit and Limbic Brain

• Papez circuit: cingulate cortex, hippocampus, hypothalamus, and anterior nucleus of the thalamus.
• Limbic brain: Papez circuit + amygdala and orbitofrontal cortex.
• Key regions are secondary to emotions, such as hippocampus and hypothalamus.

Paul Ekman's Basic Emotions

• Dr. Paul Ekman's work on expression and gesture and their role in emotion and deception.

Other Contemporary Approaches

• Feldman-Barrett theory: all emotions tap into a core affect system organized along two dimensions: pleasant-unpleasant and activation-deactivation.
• Rolls theory: constructionist approach, concerned with dimensions of reward and punishment, their presence/absence, and intensity.

Neural Substrates

• Amygdala: involved in memory, especially emotional content, fear learning, and recognizing fear.
• Insula: involved in bodily perception, pain and taste perception, disgust, and interoception.
• OFC (Orbitofrontal Cortex): computes current value of a stimulus, linked to subjective reports of pleasantness.
• Anterior Cingulate: involved in error monitoring, bodily responses to emotions, and social aspect, empathy, and exclusion.
• Ventral Striatum: reward-related, calculates difference between predicted and actual reward.

Reading Faces

• Facial Identity: fusiform face area.
• Expression Recognition & Gaze Processing: superior temporal sulcus.
• Expressions: involve the extended system, including amygdala and insula.
• Simulation Theory: we understand others by vicariously producing their current state in ourselves.

Reading Faces (continued)

• Social Referencing: emotional response of another person may lead to avoidance or interaction with a previously neutral stimulus.
• Capgras Syndrome: patients can consciously recognize the person but lack an emotional response to them, believing they were replaced with body doubles.

Eye Gaze Information

• Eyes Inform About Emotions: important for one-to-one communication.
• Eye Gaze: one can infer desire (next move) from eye gaze.

Reading Minds

• Theory-of-Mind: the ability to represent the mental states of others (e.g., their beliefs, desires, intentions).
• Empathy: the ability to appreciate others' points of view and share their experiences.
• Mirror System: neural circuits or regions that disregard the distinction between self and other.