Tuesday, August 11, 2009

Looking under the hood

Looking under the hood of language processing and language learning

The Broca’s area is a region of the brain responsible for speech articulation. It controls the motor complex which is responsible for speech production. “For a long time, it was assumed that the role of Broca's area was more devoted to language production than language comprehension. However, recent evidence demonstrates that Broca's area also plays a significant role in language comprehension. Patients with lesions in Broca's area who exhibit agrammatical speech production also show inability to use syntactic information to determine the meaning of sentences.[4] Also, a number of neuroimaging studies have implicated an involvement of Broca's area, particularly of the pars opercularis of the left inferior frontal gyrus, during the processing of complex sentences.(Wikipedia)

“More recently, Broca's area has been implicated in music processing, leading some researchers to suggest music may be processed as a language. Imaging studies have revealed that professional musicians trained at an early age have an increased volume of gray matter in Broca's area. Broca's area is part of a language and music processing network that includes Wernicke's area, the superior temporal sulcus, Heschl's gyrus, planum polare, planum temporale, and the anterior superior insular cortices.” Link

(Comment: Broca's area is essential for producing language and mediating grammar. The Broca’s area of the brain of Emil Krebs was larger and organized differently from that of monolingual men. It is unclear whether this was from birth or whether it was due to language learning).

Superior temporal gyrus: "a gyrus in the upper part of the temporal lobe. Contains the primary auditory cortex. The anterior part of this region has been implicated in generating the aha! experience of insight.” Link

Averbia is a specific type of anomia in which the subject has trouble remembering only verbs. This is caused by damage to the frontal cortex, in or near Broca's area.

Brain imaging findings:

Thinking about words makes the Broca’s area light up.
Thinking about words and speaking generates widespread activity.
Inner speech – Broca’s area active
Word retrieval (lexical information) – Broca’s involved
Prosody (musical intonation of speech) – Broca’s involved
Preparing to speak – Broca’s area active

The superior temporal gyrus contains several important structures of the brain, including: Brodmann areas 41 and 42, marking the location of the primary auditory cortex, the cortical region responsible for the sensation of sound; Wernicke's area, Brodmann 22p, an important region for the processing of speech so that it can be understood as language. (Wikipedia)

The auditory association area (Wernicke's area, or area 22) is an important region for the processing of acoustic signals so that they can be distinguished as speech, music, or noise. It is located within the temporal lobe of the brain, posterior to the primary auditory cortex. It is considered a part of the temporal cortex. It stores memories of sounds and permits perception of sounds. Wernicke's area (posterior part of the superior temporal gyrus) is connected to Broca's area via the arcuate fasciculus, a neural pathway, and to the visual cortex via the angular gyrus. It is the semantic processing center of the brain which plays a significant role in the conscious comprehension and interpretation of spoken words by both the listener and speaker. Words are not understood until they are processed by Wernicke’s area.

Primary auditory cortex. Located at the superior margin of the temporal lobe. Receives information related to pitch, rhythm and loudness.

Basal ganglia are large knots of nerve cells deep in the cerebrum. Structures contained in the basal ganglia include the amygdala, globus pallidus, and striatum (containing the caudate nucleus and the putamen). The basal ganglia (or basal nuclei) are interconnected with the cerebral cortex, thalamus and brainstem. They are associated with motor control and learning and participate in concert with the cortex in cognition and emotions. Parkinson's disease is an affliction of the basal ganglia. New (controversial) evidence suggests that these structures may also be involved in language processing.

“The Declarative/Procedural Model of Pinker, Ullman and colleagues claims that the basal ganglia are part of a fronto-striatal procedural memory system which applies grammatical rules to combine morphemes (the smallest meaningful units in language) into complex words (e.g. talk-ed, talk-ing). We tested this claim by investigating whether striatal damage or loss of its dopaminergic innervation is reliably associated with selective regular past tense deficits in patients with subcortical cerebrovascular damage, Parkinson’s disease or Huntington’s disease. We focused on past tense morphology since this allows us to contrast the regular past tense (jump-jumped), which is rule-based, with the irregular past tense (sleep-slept), which is not…. All patient groups showed normal activation of semantic and morphological representations in comprehension, despite difficulties suppressing semantically appropriate alternatives when trying to inflect novel verbs. This is consistent with previous reports that striatal dysfunction spares automatic activation of linguistic information, but disrupts later language processes that require inhibition of competing alternatives.

It seems more likely that neocortical regions are critical for this processing rather than the basal ganglia. Such a conclusion would be consistent with our recent finding that healthy volunteers show increased activation of the left inferior frontal gyrus and the left superior temporal gyrus when processing the regular past tense than irregular forms or words matched to past tense phonology (Marslen-Wilson et al., 2003)."

The basal ganglia and rule-governed language use: evidence from vascular and degenerative conditions by C. E. Longworth, S. E. Keenan, R. A. Barker, W. D. Marslen-Wilson and L. K. Tyler

(Comment: language processing is different from language learning).

“In the case of adult language learning, for example, proceduralized linguistic input may eventually be stored in the neocortex, but only after making a loop through the circuits of the basal ganglia… Immersion learning is slightly more procedural in nature, whereas classroom learning is slightly more declarative. Although in the past several decades, some teaching methods have endeavored to change this.”

The Neurobiology of Learning
By John H. Schumann, Sheila E. Crowell, Nancy E. Jones, Namhee Lee

The striatum is a subcortical part of the cerebrum. It is the major input station of the basal ganglia system and the part of the basal ganglia with the most complex shape.

"At a subcortical level, the main connections are located at the striatum. There is convincing evidence that highly automatized language skills are processed at this level. Agloti, Beltramello, Girardi, and Fabbro (1996) reported a case of aphasia where the patient had been bilingual in a Venetian dialect and standard Italian, two rather different languages. Her first and daily language was Venetian. However, after a stroke, she lost her Venetian language completely and was only able to speak standard Italian. It turned out that her brain damage was located at the subcortical level at striatum."

"Recent functional neuroimaging studies support a likely role for the dominant striatum in language, as activations were found during various different tasks such as speech, syntactic processing, lexical processing, word memorisation, word retrieval, and writing."


Comment: The brain learns in two different ways. One, called declarative learning, involves the medial temporal lobe and deals with learning active facts that can be recalled and used with great flexibility. Declarative learning and memory (also called explicit learning or, simply, memory) involves rapid learning, conscious recollection, and explicit declaration. It happens after language development. It is characterized by analytical, language-based, memory-dependent approach to acquiring and retaining knowledge. Distraction-free studying is more efficient and effective for this type of learning.

The second, involving the striatum, is called habit learning. There is convincing scientific evidence that highly automatized language skills are processed at this level.

The two types of learning compete with each other, and when someone is distracted habit learning takes over from declarative learning. One learns better particular habitual tasks while declarative learning suffers. The declarative and procedural memory systems interact both cooperatively and competitively in the acquisition and use of language.

And what is the outcome of successful language learning?

"Expert language learners attain a level of competence that is virtually comparable to that of native speakers (Coppieters 1987; Birdsong 1992,1997). The final state of these speakers is near-native – their “mental package” must look a lot like a native grammar since it includes phonological, morphological and syntactic rules. The documentation strongly suggests that these expert L2ers do indeed possess a grammar and not simply a collection of cognitive facts and strategies. Furthermore, while an intermediate L2 grammar appears to be less complete than the expert’s, it shares many of the characteristics of the superior L2er. Third, L2ers acquire knowledge that they are not taught and which does not transfer from the L1… This kind of evidence strongly supports the claim that knowledge of L2 is internally systematic, procedural and untaught; it is grammatical, not exclusively cognitive.

The documentation furnished by brain scans and neuro-electrical measurement complements and corroborates studies of language deprivation indicating a post-Critical Period loss of ability to acquire L1 morphosyntax (Curtiss 1988), but a persistent ability to acquire lexical items… It is evident that the neurological “etching” (Platzack 1996) of L1 must take place during the first five years of life for grammar to be really well established. If the L1 is so engraved, there is a grammar template for the L1 and for future additional languages. Child bilinguals have a double grammar in the Broca’s area of the brain, while adult bilinguals construct a second (L2) grammar separate from L1, BUT IN THE SAME APPROXIMATE REGION (Kim et al. 1997). Given the (often subtle) deficiencies of L2 grammars, one may infer that the L2 grammar is less deeply engraved. In contrast to grammatical knowledge, lexical information for both L1 and L2 is stored and accessed in a similar manner (Weber-Fox and Neville 1999)…. The L1 provides the template that permits the acquisition of L2, but ironically also interferes with that acquisition by the very depth of L1 neurological engraving…”

The second time around by Julia Rogers Herschensohn

An opposing view:

"Among the factors that typically lead to native-like proficiency in L2, aptitude, meaning the ability to learn explicitly, becomes one of the major variables. The fact that cognitive aptitude strongly correlates with success of L2 learning (Ehrman & Oxford, 1995) again suggests that high attainment in L2 is the result of learning rather than acquisition. All these factors are associated with learning performance in any knowledge domain subserved by declarative memory."

Declarative and Procedural Determinants of Second Languages by Michel Paradis

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