NRSC 2249 - Language

chimp and ape communication

• lack fine motor control and voluntary control

• neurological differences in language production regions

• limited repertoire of sounds

anatomy of language

• frontal and posterior temporal regions

• varied considerably with anatomical folding

asymmetries of anatomy

• differences present in utero around 31 weeks

• not clear whether causally related to language development

lateralization in split brain

• right side:

  • object manipulation

  • right visual field can be described without difficulty

• left side:

  • no description possible from left visual field or hand

• supports idea that left hemisphere is dominant for language

aphasia

partial or complete loss of language following brain damage

Broca’s aphasia

• difficulty with speech production

• awareness of deficit

• lesions to left lateral frontal lobe

  • patient “Tan”

Wernicke’s aphasia

• difficulty with language comprehension

• speech is fluent but lacks meaning

• may not be aware of deficit

• damage to left superior temporal gyrus

conduction aphasia

• difficulty repeating and verbalizing words

• language comprehension and production are preserved

  • fluent and grammatically correct speech

• damage to arcuate fasciculus (connection between Broca/Wernicke)

anomia (anomic aphasia)

• inability to retrieve words or name objects/concepts

  • word-finding difficulty

• not a deficit for recognizing objects

• damage to left temporal and/or parietal

mental lexicon

mental storehouse of a person’s vocabulary and knowledge of words

semantics

meaning of words

syntax

how words combine to form sentences

orthography

visual context of words

phonology

sounds of words

accessing from mental lexicon

matching input to stored representations in the mental lexicon

selecting from mental lexicon

choosing the appropriate word to convey meaning in context; includes frequency, semantics, and syntax

integrating from mental lexicon

fitting words into larger semantic and syntactic structure to form phrases and sentences

morpheme

smallest unit of meaning in a language (free and bound)

free morpheme

can stand alone as words (dog, happy)

bound morpheme

must be attached to other morphemes to form meaning (un-, -s)

phoneme

smallest unit of sound in a language

frequency

how often a word occurs in a language

semantic relationship

words that are related in meaning to each other, stored near in mental lexicon

semantic paraphasis

• deficit in mental lexicon

• produce words that are semantically related, but not phonological similar

  • “table” instead of “chair”

• common with Wernicke’s aphasia

progressive semantic dementia

• deficit in mental lexicon

• progressive loss in semantic knowledge, difficulty identifying and naming objects and words

  • impaired conceptual system, syntax intact

category-specific deficits

• difficulty processing words from specific semantic categories

  • suggests that categories of words are represented differently

categories of semantic information

• left temporal lobe

• broad (posterior) → specific (anterior)

Wernicke-Lichtheim model

• classic model of language processing

• auditory inputs → Wernicke → conceptual information stores → Broca → motor outputs

• Wernicke ← arcuate fasciculus → Broca

challenges to classical model of language

• language regions variable across people

  • regions implicated in multiple functions

  • many other regions contribute to language

• double dissociation in aphasia patients less clear

• separation of language functions not predicted by model

• organization of language depends on time of acquisition

Pandemonium model (Oliver Selfridge)

• 4-stage model for visual word recognition

• image demon → feature demons → cognitive demons → decision demon

• serial processing, bottom-up

image demon

• first component of pandemonium model

• sensitive to particular features, such as line or edges

  • compete with each other to detect strongest features

• records image from retina

feature demon

• second component of pandemonium model

• receive input from image demons

• sensitive to combination of image features

cognitive demon

• third component of pandemonium model

• receive input from feature demons

• higher-level concepts used to interpret features

  • sensitive to combination of features

decision demon

• fourth component of pandemonium model

• selects cognitive demon with the highest activation level

Interactive Activation Model (McClelland and Rumelhart)

• 3-stage model of visual word recognition

• importance of interactions among levels of processing

• parallel, top-down with excitatory + inhibitory processes

feature stage

• first stage of interactive activation model

• feature detectors that respond to simple visual features, such as edges or lines

  • organized into lower-level (basic) and higher-level (complex)

letter stage

• second stage of interactive activation model

• receive input from feature detectors to activate letter units

  • feature detector input and connections between letter units

word stage

• third stage of interactive activation model

• receives input from letter units to activate word units

• influenced by activation of letter units and connections between word units

neural basis of visual word recognition

• unlikely to be understood at the neuronal level

• animal studies not likely to be helpful in human systems

visual word form area

• specialized area involved in visual recognition of words and letters

• left occipitotemporal cortex (near fusiform gyrus)

• connected with perisylvian language areas, including Broca

alexia

• inability to read, despite intact visual and language abilities

• damage to visual word form area

neural basis of spoken word recognition

• primary auditory cortex (A1): basic auditory features such as frequency and duration

• multiple parallel and hierarchical pathways

  • STS/SG (surrounding A1): maps sounds onto corresponding meaning

  • sensitivity decreases moving away fro A1

dyslexia

• developmental disorder, subjects have difficulty reading fluently and accurately

• difficulties in word recognition and phonological processing (recognizing/manipulating sounds of language)

  • problems with left hemisphere language areas

  • compensatory activity in left anterior and right hemisphere

neural basis of syntactic processing

• parsing: process of analyzing gramatical structure of a sentence

• aphasia patients with syntactic difficulties show damage in anterior superior temporal gyrus

• P600 is key component

P600

• key component in syntactic processing

• event-related potential (ERP) that occurs 600 ms after onset of syntactic anomaly

  • more positive for syntactically anomalous stimuli

neural basis of semantic processing

• N400 is key component: ERP that occurs 400 ms after semantically meaningful stimulus (word or picture)

  • more negative for semantically incongruous stimuli

  • reduced and delayed for Broca’s aphasia

P560

• elicited when words are semantically congruent, but physically different

• positive response

memory-unification-control model

• series of cycles in which information is retrieved, integrated, and unified

• emphasizes importance of bottom-up and top-down processing

• role of working memory in language processing

  • control of attention, integration of information

memory system (MUC)

• storing and retrieving linguistic information

  • lexicon: words and meanings

  • episodic: context in which words are used

unification system (MUC)

• integrating phonological, semantic, and syntactic information from different sources

• creates a unified representation of the meaning of a sentence

control system (MUC)

• regulates flow of information between memory and unification systems

• coordinates language processing with other cognitive processes, such as attention and working memory

dorsal pathways (language)

• two pathways in spoken language processing

  • posterior temporal → frontal

• acoustic features of speech (articulation)

  • Broca’s area → superior temporal gyrus

• maps onto motor representations for speech production

  • → premotor cortex

ventral pathways (language)

• two pathways in spoken language processing

  • posterior temporal → anterior temporal, frontal operculum

• semantic content of speech, integration with memory

• comprehending words

Levelt’s model

• serial model of speech production

• conceptual preparation → lexical selection → morphological and phonological encoding → phonetic encoding → articulation

conceptual preparation (Levelt)

• first step in serial speech production

• generates idea to be expressed and mental representation of of the message to be conveyed

lexical selection (Levelt)

• second step in serial speech production

• selects syntactic properties of appropriate words

  • retrieving words from mental lexicon

morphological and phonological encoding (Levelt)

• third and fourth steps of serial speech production

• morphemes added, then encodes selected words into phonological representation

  • syllable count and stress patterns

phonetic encoding (Levelt)

• fifth stage of serial speech production

• plans and executes movements of articulatoria, such as lips and tongue, to produce appropriate speech sounds

  • creation of a motor plan

articulation (Levelt)

• sixth step of serial speech production

• produces sounds necessary to convey linguistic message

  • executes motor plan, produces appropriate articulator motion

Hickok’s Hierarchical State Feedback Control (HSFC)

• parallel processing in speech production

• starts at conceptual representation (similar to Levelt)

  • word level → splits into motor and sensory phonological

• speech production uses a feedback loop

  • sensory information used to adjust and modify motor commands

apraxia

• difficulty planning, coordinating, and executing necessary movements for speech production

  • no weakness or paralysis of speech muscles

• can result from brain damage or be developmental in nature