lexical access

8/10/2019 lexical access

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Lexical access

! The process by which the basic sound-meaning

connections of language, i.e., lexical entries, are

activated.

! How to find lexical access in the brain (of a healthy

human)?


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A. Manipulate thepresenceof lexical access. Condition 1: + Lexical Access

Condition 2: - Lexical Access

But setting up a situation where only the presence oflexical access is manipulated is tricky because moststimuli that even remotely resemble words activate actuallexical entries.

B. Manipulate the difficultyof lexical access. Condition 1: Hard Lexical Access

Condition 2: Easy Lexical Access

This manipulation is more straightforward to set up sincebehavioral research has provided us with a detailedunderstanding of what factors affect lexical access.

How to find lexical access in the brain?


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! The ease of accessing a lexical entry always depends on

the level of activation in that entry prior to access.

! The pre-access level of activation primarily depends on two

factors: The resting level of activation in the entry.

! Each lexical entry has certain resting level of activation.

! This resting level is primarily a function of how frequently you

access the word. Frequent access leads to a higher resting level.

Context (i.e., what other entries youve just accessed)

What affects lexical access?


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Cognitive processes involved inCognitive processes involved in

lexical accesslexical access

time

levelofactivation

resting level

Stimulus: TURN

TURN

TURNIP

TURFTURTLE

ActivationActivation SelectionSelectionCompetitionCompetition


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Spread of activation on the basis of meaning


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1 2 3 4 5 6

Frequency Category (Frequent -- Infrequent)

Categories (n/Million):

1: 700

2: 140

3: 30

4: 6

5: 1

6: .2

1: number

2: ask3: wheel

4: candle

5: clam

6: snarl

Effect of frequency on lexical decision

(Embick et al. 2000)


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Context effects

! Repetition priming.

! Semantic priming

! Phonological priming.


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Semantic priming

PRIME TARGET


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Semantic priming


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doctor

Repetition

! doctor (obviously) activates the lexical representation DOCTOR verystrongly.

! Because of this robust activation, a subsequent presentation ofdoctor will show repetition priming for quite some time, even ifthere are intervening words in the list.


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Phonological priming

! Complicated. Effect depends on the stimulus

onset asynchrony (SOA)

SOA: interval between prime and target


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time

levelofactivation

resting level

TURN

TURN

TURNIP

TURFTURT

LE


TURF

PRIME TARGET

TURF is presented before its activation starts to decrease due to

inhibition from TURN "Positive priming compared to unrelated

control (e.g., CLOCK - TURF)


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TURF is presented after its activation has been suppressed by

TURN"No priming or even slower processing times than in an

unrelated control (e.g., CLOCK - TURF).

time

levelofactivation

resting level

TURN

TURN

TURNIP

TURFTURT

LE


PRIME

TURF

TARGET


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A. Manipulate thepresenceof lexical access. Condition 1: + Lexical Access

Condition 2: - Lexical Access

But setting up a situation where only the presence of

lexical access is manipulated is tricky because moststimuli that even remotely resemble words activateactive actual lexical entries.

B. Manipulate the difficultyof lexical access.

Condition 1: Hard Lexical Access Condition 2: Easy Lexical Access

This manipulation is more straightforward to set upsince behavioral research has provided us with adetailed understanding of what factors affect lexical

access.

How to find lexical access in the brain?


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Millisecond by millisecond MEG measurement of the brain

activity elicited by visual words in the lexical decision task:

CAT

0 200 400 600 800 1000

Time [msec]

Response

! What part of this activity is sensitive to Frequency?

Repetition?

Semantic relatedness?

Phonological relatedness?


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MEG components elicited by visual words

What is the time course of lexical access?

M100 M170 M250 M350

100-150ms 150-200ms 200-300ms 300-400msAveraged response to

visual words

100170 250 350

1st MEG

component

showing a

reliable effect

of frequency


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M350 data collected during the same experiment:

1 2 3 4 5 6

Frequency Category (Frequent -- Infrequent)

Categories (n/Million):

1: 700

2: 140

3: 30

4: 6

5: 1

6: .2

1: number

2: ask3: wheel

4: candle

5: clam

6: snarl


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CAT

0 200 400 600 800 1000

Time [msec]

Response

! Finding: Left temporal activity around ~350ms is sensitive tolexical frequency in the lexical decision task.

! What follows from this?

Either: the M350 reflects lexical access.

Or: the M350 reflects some process the follows lexicalaccess.! If lexical access occurs faster due to high frequency, then all

subsequent processing is presumably speeded up, too.

! M350 could be related to the experimental task, I.e., it could reflectthe lexical decisions.


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Is the M350 task-related?

! Pylkknen, Stringfellow, & Marantz (2002): Set up a situation where activation is speeded up while

lexical decisions are simultaneously slowed down. Doesthe M350 show a speed-up or a slow-down?


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time

levelofactivat

ion

resting level

Stimulus: TURN

TURN

TURNIP

TURFTURTLE


Activation isActivation is

facilitatedfacilitated

Selection isSelection is

slowed downslowed downWhich way wouldWhich way would

the M350 move?the M350 move?


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Method: Manipulate the degree of competition by varying

the phonotactic probability of the stimuli

! Phonotactic probability: How common the soundsand the sound sequences of the stimulus are.

! Words and nonwords with a high phonotacticprobability: mile, pick, fan, line

sipe, tane, rean, cade

! Words and nonwords with a low phonotacticprobability: house, lock, peep, town

theeg, yush, nirg, veige


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Effect of phonotactic probability

! On the on the hand, stimuli that have a high phonotacticprobability activate the lexicon faster. Just like frequent words are faster to process, frequent sounds are

also faster to process.

! On the other, stimuli that have a high phonotactic probabilityactivate lots of lexical entries. This slows down selection (or in the case of a nonword, the decision

that the stimulus is not a word) since there are many alternatives toconsider.

! High phonotactic probability correlates tightly with the densityof the words similarity neighborhood. Neighborhood density.


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Effect ofEffect of phonotacticphonotactic probability:probability:

later inhibitionlater inhibition

RTHigh probability: MIDE

YUSH RTLow probability:

mile mild might

migrate mike mime

mine mire mind

mite migraine micro

neighborhood activated

yuppie yuccayuck yum

neighborhood activated

Competition

effect

(Vitevich and Luce 1998, 1999)

Lexical decision (high level)

Requires searching through the lexicon.

RTs to nonwords with a high phonotactic probability

are slowed down.


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time

level

ofactivation

resting level

Stimulus: TURN

TURN

TURNIP

TURFTU

RTLE


FacilitatesFacilitates

activationactivation

slows downslows down

selectionselectioninduces intenseinduces intense

competitioncompetition

HighHigh phonotacticphonotactic probabilityprobability


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time

level

ofactivation

resting level

Stimulus: TURN

TURN

TURNIP

TURFTU

RTLE


Then high probabilityThen high probability/

density should delaydensity should delayM350 latenciesM350 latencies

If M350 = SelectionIf M350 = Selection (or later processing)(or later processing)


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time

level

ofactivation

resting level

Stimulus: TURN

TURN

TURNIP

TURFTU

RTLE


If M350 = ActivationIf M350 = Activation

Then high probability/Then high probability/

density should speed updensity should speed upM350 latenciesM350 latencies


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JIZE, YUSHMIDE, PAKENonword

PAGE, DISHBELL, LINEWord

Low probabilityHigh probability

Four categories of 70 stimuli:

Lexical decision.

(Pylkknen, Stringfellow, Marantz, Brain and Language, 2002)

Materials (visual)Materials (visual)


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(Pylkknen, Stringfellow, Marantz, Brain and Language, 2002)

Effect of probability/densityEffect of probability/density

100

200

300

400

500

600

700

800

M170 M250 M350 RT

High probability word Low probability word

n.s.

n.s.

*

*

Words

100

200

300

400

500

600

700

800

M170 M250 M350 RT

High probability nonword Low probability nonword

n.s.

n.s.

*

*

Nonwords


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M350: (i) 1stcomponent sensitive to

lexical frequency

(ii) not affected by competition

time

lev

elofactivation

resting level

Stimulus: TURN

TURN

TURNIP

TURFTURTLE



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M350: (i) 1stcomponent sensitive to

lexical factors

(ii) not affected by competition

The M350 also is also sensitive to repetition and bothphonological and semantic relatedness, as one would expectif it indexed the access to sound-meaning connections

(Pylkknen et al. 2006).

Further, the M350 is elicited in the auditory modality, as onewould expect if it indexed the access to modality independentrepresentations.


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M350 localizations from Pylkknen

et al. (2006)

Localizations of M350 current generator


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M350 localizations from Pylkknen

et al. (2006)

Location of electrode sites whereTSA was induced.

Intact: Repetition, syllablediscrimination, speech, naming andword reading.

M350 vs. induced TSA

Boatman et al. (2000)


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M350 vs. induced TSA

The localization of TSA and M350 localizationssuggest a similar degree of between-subjectsvariance.

lexical access

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