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Language processing What are the components of language, and how do we process them?
Phonemes • Most basic components of a language. • Individual sounds • What are the phonemes of English? • What distinguishes them from each other?
Phoneme processing • Perception • Speed: Can process 15-20 phonemes per second • Categorical Perception: Speech sounds get categorized as one phoneme or another. No in-between. Ex: ‘r’ vs. ‘l’ to a Japanese speaker • Production • Co-articulation: We change the phonemes we actually use based on the other phonemes surrounding it in the speech stream
Morphemes • Smallest meaning carrying units in a language • Root Words: simple words like “book”, “run”, etc. • Affixes: Things we attach to words to modify their meaning; “-s” for pluralization, “-ed” for past tense, etc. • Interesting note: While we have standardized the spelling of morphemes when written, that doesn’t mean they are always pronounced the same.
Morpheme processing • Lexicon • Content morphemes: Morphemes that actually mean something. “-s”, “run”, etc. • Function morphemes: Morphemes that serve a gramatical purpose, but have no real meaning. “the”, “or”, etc. • People know roughly 80- to 100-thousand morphemes, stored in the lexicon.
Neurology of the Lexicon • Aphasias are deficits of language arising from brain damage. They differ from agnosias in that patients can still exhibit non-linguistic knowledge of an object. • Semantic paraphasia is where patients make errors in production by substituting semantically related words to the one intended. • Semantic dementia: Progressive semantic disorder largely associated with damage to the left inferior temporal lobe.
Broca’s aphasia • Patients tend to have significant deficits in speech production; sometimes limited to producing only a single word or syllable. • Even in less severe cases, production of function words is severely diminished. • Also have a hard time understanding more complex syntactical structures, such as passive constructions. • Corresponds with damage to the left inferior frontal lobe.
Wernicke’s aphasia • Patients experience significant difficulties in understanding either written or spoken speech. • Speech production is fluent and grammatical, but nonsensical. • Single word production tends to exhibit semantic parahpasia. • Wernicke’s area is located in the posterior temporal lobe.
Conduction aphasia • Neural pathways in the arcuate fasciculus connect Wernicke’s area to Broca’s area (one-way). • When this pathway is damaged, patients have difficulties with word usage. • The also have difficulties repeating things they heard, or spontaneously generating speech.
Syntax • Syntax (grammar) is the set of rules for combining morphemes. It gives language its meaningful structure. • Are all languages derived from a common universal grammar? • Chomsky thought so.
Phrase structure grammar • Phrase structure rules are rules for deconstructing complex symbols into sets of simpler symbols. • S -> NP VP • NP -> (det) (AdjP) N (PP) • VP -> (AdvP) V (NP) (PP) • det -> a, an, the • Knowing the phrase structure of a sentence allows us to disambiguate it: • They are cooking apples. • Bob greeted his friend by the mailbox
Transformational grammar • Chomsky said phrase structure grammars were too simple. • How can we capture the semantic equivalence of syntactically different sentences? • Bob threw the frisbee. • The frisbee was thrown by Bob.
Neurology of syntax • Agrammatic aphasia exists in patients who do not appear to have semantic deficits, but have significant difficulty in understanding sentences. • They largely produce very short, agrammatic sentences similar to those of a child.