Lexical access The process by which the basic sound-meaning

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

How to find lexical access in the brain (of a healthyhuman)?

A. Manipulate the presence of 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 difficulty of 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?

The “ease” of accessing a lexical entry always depends onthe level of activation in that entry prior to access.

The pre-access level of activation primarily depends on twofactors:• 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 you’ve just accessed)

What affects lexical access?

Cognitive processes involved inCognitive processes involved inlexical accesslexical access

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Stimulus: TURN

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ActivationActivation SelectionSelectionCompetitionCompetition

Spread of activation on the basis of meaning

Frequent words are accessed faster than rarewords.• Comprehension: Faster lexical decision times.• Production: Faster naming times.

Higher resting level allows them to reach athreshold for recognition faster.

Effect of frequency

1 2 3 4 5 6

Frequency Category (Frequent -- Infrequent)

Behavioral Data: Reaction Time

Categories (n/Million):

1: 7002: 1403: 30 4: 6 5: 1 6: .2

1: number2: ask3: wheel4: candle5: clam6: snarl

Effect of frequency on lexical decision(Embick et al. 2000)

Context effects

Repetition priming. Semantic priming Phonological priming.

Semantic priming

PRIME TARGET

Semantic priming

doctor

Repetition

‘doctor’ (obviously) activates the lexical representation DOCTOR verystrongly.

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

Phonological priming Complicated. Effect depends on the stimulus

onset asynchrony (SOA)• SOA: interval between prime and target

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ActivationActivation SelectionSelectionCompetitionCompetition

TURF

PRIME TARGET

TURF is presented before its activation starts to decrease due toinhibition from TURN Positive priming compared to unrelatedcontrol (e.g., CLOCK - TURF)

TURF is presented after its activation has been suppressed byTURN No priming or even slower processing times than in anunrelated control (e.g., CLOCK - TURF).

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PRIME

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TARGET

A. Manipulate the presence of 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 activateactive actual lexical entries.

B. Manipulate the difficulty of 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 lexicalaccess.

How to find lexical access in the brain?

Millisecond by millisecond MEG measurement of the brainactivity 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?

MEG components elicited by visual wordsWhat is the time course of lexical access?

M100 M170 M250 M350100-150ms 150-200ms 200-300ms 300-400ms

Averaged response tovisual words

100 170 250 350

1st MEGcomponentshowing areliable effectof frequency

1 2 3 4 5 6

Frequency Category (Frequent -- Infrequent)

Behavioral Data: Reaction Time

Categories (n/Million):

1: 7002: 1403: 30 4: 6 5: 1 6: .2

1: number2: ask3: wheel4: candle5: clam6: snarl

Effect of frequency on lexical decision(Embick et al. 2000)

M350 data collected during the same experiment:

1 2 3 4 5 6Frequency Category (Frequent -- Infrequent)

Latency of m350 Component

Categories (n/Million):

1: 7002: 1403: 30 4: 6 5: 1 6: .2

1: number2: ask3: wheel4: candle5: clam6: snarl

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 lexical

access. 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 reflect

the lexical decisions.

Is the M350 task-related?

Pylkkänen, 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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Stimulus: TURN

TURN

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ActivationActivation SelectionSelectionCompetitionCompetition

Activation isActivation isfacilitatedfacilitated

Selection isSelection isslowed downslowed down

Which way wouldWhich way wouldthe M350 move?the M350 move?

Method: Manipulate the degree of competition by varyingthe 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

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 word’s similarity neighborhood.• “Neighborhood density.”

Effect of Effect of phonotactic phonotactic probability:probability:early facilitationearly facilitation

RT

• Same/different task (“low level”)Are these two stimuli the same or different?RTs to words and nonwords with a high phonotacticprobability are speeded up.

High probability: MIDE

RTYUSHLow probability:

Sublexicalfrequencyeffect

(Vitevich and Luce 1998, 1999)

Effect of Effect of phonotactic phonotactic probability:probability:later inhibitionlater inhibition

RTHigh probability: MIDE

YUSH RTLow probability:

mile mild mightmigrate mike mime

mine mire mindmite migraine micro

neighborhood activated

yuppie yuccayuck yum

neighborhood activated

Competitioneffect

(Vitevich and Luce 1998, 1999)

• Lexical decision (“high level”)Requires searching through the lexicon.RTs to nonwords with a high phonotactic probabilityare slowed down.

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ActivationActivation SelectionSelectionCompetitionCompetition

FacilitatesFacilitatesactivationactivation

slows downslows downselectionselection

induces intenseinduces intensecompetitioncompetition

High High phonotactic phonotactic probabilityprobability

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ActivationActivation SelectionSelectionCompetitionCompetition

Then high probability/Then high probability/density should delaydensity should delayM350 latenciesM350 latencies

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

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ActivationActivation SelectionSelectionCompetitionCompetition

If M350 = ActivationIf M350 = ActivationThen high probability/Then high probability/density should speed updensity should speed upM350 latenciesM350 latencies

JIZE, YUSHMIDE, PAKENonword

PAGE, DISHBELL, LINEWord

Low probabilityHigh probability

• Four categories of 70 stimuli:

• Lexical decision.

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

Materials (visual)Materials (visual)

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

Effect of probability/densityEffect of probability/density

100

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M170 M250 M350 RT

High probability word Low probability word

n.s.

n.s.

*

*

Words

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M170 M250 M350 RT

High probability nonword Low probability nonword

n.s.n.s.

*

*

Nonwords

M350: (i) 1st component sensitive to lexical frequency(ii) not affected by competition

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M350: (i) 1st component 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(Pylkkänen et al. 2006).

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

M350 localizations from Pylkkänenet al. (2006)

Localizations of M350 current generator

M350 localizations from Pylkkänenet al. (2006)

Location of electrode sites whereTSA was induced.Intact: Repetition, syllablediscrimination, speech, naming andword reading.

M350 vs. induced TSA

Boatman et al. (2000)

M350 vs. induced TSA

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