Words in the brain Slide #1

김 민 경

2008. 10. 09

Chap 4. Words in the brain

Words in the brain Slide #2

Objectives

• To explain brain activity (neurobiological organization and operation) of word processing

• Mainly,(1) Word-Form Webs:

Cognitive processes are realized as the activity of distributed neuron ensemble that act as functional units.

(2) Category-Specific Word Webs: When humans process words from different categories, sets of cortical areas become active differentially.

(3) The Time Course of Lexical and Semantic Activation

Words in the brain Slide #3

Functional Webs in the cortex (1/3)

• Functional Web is a network of strongly connected neurons• Representation & Process of words and concepts of different kinds Become the cortical representation of an object

• Information from different modalities (object features; shape, smell, and smooth fur of a cat) is represented in distant cortical areas linked through long-distance connections

Processed by binding of the features of an object (ex. cat-concept )

• Evidence for Functional Webs• A significant portion of the web’s neurons are active whenever the concept of an object is being processed (ex. a web for the concept CAT)

• The function of the web depends on the intactness of its member neurons• If neurons in the functional web are strongly linked, they should show similar response properties in neurophysiological experiments

1. Word-Form Webs

Words in the brain Slide #4

Functional Webs in the cortex (2/3)

1. Word-Form Webs

“The functional webs realizing phonological word forms may be distributed over the perisylvian area of the dominant left hemishpere. Circles represent local neuron clusters and lines represent reciprocal connections between them.”

Words in the brain Slide #5

1. Word-Form Webs

Word vs. Pseudo

(b) Word presentation induced stronger gamma-band responses in the 30Hz range in particular over the left hemisphere (Reverberatory circuits within word webs high-frequency responses)

(c) MMNm: stronger in response to words compared to pseudo-words

(d) Response was localized in the left superior temporal lob

Functional Webs in the cortex (3/3)

Words in the brain Slide #6

Visually Related & Action Words (1/2)

2. Category-Specific Word Webs

Meaning of a verb

Meaning of a visual object

• Word Webs (1) Word form information in perisylvian areas

(2) Processing information about perceptions & actions in more widespread cortical areas

Words in the brain Slide #7

Visually Related & Action Words (2/2)

2. Category-Specific Word Webs

(B) fMRI dataLeft panels: a pre-motor area and a middle temporal area are more strongly excited by words for tools than words for animalsRight panels: an occipital area is more strongly excited by words for animals than words for tools

(A): schematic predictions

Words in the brain Slide #8

fMRI (one subject’s data):Black areas: stronger activation for foot-related verbs (eg. Kick)White areas: stronger activation for hand-related verbs (eg. Pick)

Structure of somatotopic maps in motor cortex

Sub-types of Action Words 2. Category-Specific Word Webs

Words in the brain Slide #9

The Time Course of Lexical & Semantic Activation

• Lexical Status & Semantics determine the brain response• The differences between semantic word categories can appear early in the neurophysiological brain response

• 100~200ms after stimulus onset• where differences between words & pseudo-words were found Lexical & Semantic brain processes occur near-simultaneously

• Lexico-semantic activation has two distinct steps(1) Access to the representation (ignition of the cell assembly); ~250ms(2) Active memory or reverberation; 250ms~

Words in the brain Slide #10

Conclusion

• Differential neurophysiological responses to words and pseudowords• Differential topographies of brain responses to action- and visually-related words

• Differential topographies of brain responses to action verbs related to different body parts

• A limitation: considerations are restricted to the level of single worlds• Affixes• Grammatical or functional words ex) if, is• A word chain

Words in the brain Slide #11

Discussion

• Multiple connections between form and meaning• Implication: parts of the phonological representation connect to parts of the meaning

• Example: walk - WALK • [w-] or [-k] for action with legs?