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From thought to language
Communicating in Words

HelpLink : Broadcast segment on the discovery and significance of mirror neuronsLink : Mirror NeuronsLink : The Origin of Speech
Link : How do we understand movements? Mirror neurons as a link between movement and language processingLien : Right hand, left brain: genetic and evolutionary bases of cerebral asymmetries for language and manual action
Original modules
Tool : Sign LanguageSign Language

The possible involvement of mirror neurons in verbal communication suggests that we may perceive phonemes just as much through the visual modality (seeing how someone’s mouth moves while they make these sounds) as through the auditory modality (hearing the sounds themselves).

The “McGurk effect”, discovered in the mid-1970s by English researcher Harry McGurk, supports this idea that speech perception is multimodal. McGurk had subjects watch and listen to a video in which someone spoke one syllable while a different syllable was substituted for it on the sound track. The subjects perceived neither of these syllables, but rather a third one that was different from them both. For example, when the subjects watched someone saying “ga” while they heard someone saying “ba”, the vast majority of them perceived the sound as “da”!

Link : The McGurk Effect: hearing lips and seeing voicesExperience : What am I saying?Experience : McGurk DescriptionLink : BA+GA=DA
Experience : The McGurk Effect:Does Age Matter?Link : Lecture labiale et clones parlants

Mirror neurons were discovered by Italian physiologist Giacomo Rizzolatti in 1992. They have been the subject of much discussion ever since, because they represent a plausible basis for the development of an intentional communication system such as human language. More specifically, mirror neurons may enable one animal to mimic the movements of the limbs or mouth of another, so as to copy a gesture or reproduce a sound to which a meaning is attached. In this way, over time, two individuals might come to share a common vocabulary.

This hypothesis fits rather neatly with the theory of a gestural origin of language. According to this theory, in the course of human evolution, a portion of the brain areas responsible for motor control assumed motor control of the larynx. (As an Italian, though, Rizzolatti would surely be among the first to acknowledge that hand gestures still play an important role in human language today, complementing that of speech.)

The great effectiveness of the various forms of sign language used by the deaf is yet another example of the complementary roles that the hands and mouth play as communication tools. Hence it may well be no accident that both the hands and the mouth have mirror neurons assigned to them in the brain.

This hypothesis also fits with the inferences drawn by American psycholinguist Alvin Liberman, who as early as 1965 proposed his motor theory of speech perception. According to this theory, people understand words by comparing and imitating a speaker’s articulatory gestures with their own motor repertoire, and then form a lasting association between these gestures and the actual words that they have heard being spoken.

Other researchers have shown that humans also have mirror neurons for auditory phenomena. The same neurons are activated when someone performs an action that produces a sound as when they simply hear the sound that this action produces.

Mirror neurons have been shown to have some other interesting characteristics as well. First of all, they will be activated when you see someone else’s hand grasp an object, but not when you see a tool grasp the same object. The explanation is that unlike tools and other human artifacts, human body parts are represented in the motor and premotor areas of the brain’s frontal lobes. Second—and here is where the implications for language become really interesting—mirror neurons do not react to just any movements of the hand or mouth, but only to movements that are involved in goal-directed actions.

In other words, it is only when an action has a meaning that it activates the mirror neurons. Their response is thus associated with the expression of intentionality—that is, with the purpose of the gesture observed. For example, certain mirror neurons that are activated when a monkey manipulates an object will remain quiet when the monkey uses the same muscles, connected to the same neurons, to perform a similar action for a different purpose, such as to scratch itself or to pick an insect out of its fur.

It is becoming more and more apparent that the brain’s motor system does not only control movements but can also in a certain sense read the actions performed by other individuals. Mirror neurons may thus play a fundamental role in all human social behaviour.

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