Psychology of LanguageProf. Jon Sprouse

02.07.13:

UCICOGNITIVESCIENCES

synlab

PSYCH 150 / LIN 155

Activation and Selection

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The activation model suggests a two-stage process of lexical access

p kt f

b gd

y a i

activ

atio

n

time

activ

atio

n

time

kptn kptv

captain captive

The fact that phonetically similar words will be activated at the same time as the target word suggests two stages to lexical access:

1. Activation of the (phonetically similar) candidate set.

2. Selection of the target word

2

electionelectricity elect elector electorate

elated elapse ellipse elastic

Stage 1: Activation of a competitor set

p kt f s ht m l

b gd v z d n rw

y a i e ou

avow abuse eclipse eschew

l k nelection

As the physical stimuli unfolds, several potential words are activated based on their similarity to the phonetic signal.

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election

avow abuse eclipse eschew

electricity elect elector electorate

elated elapse ellipse elastic

Stage 2: Selection of the target word

p kt f s ht m l

b gd v z d n rw

y a i e ou

l k nelection

The target word must then be selected from the candidate set (based on relative activation levels and other top-down information)

4

Capturing the activation of competitors in the model

activ

atio

n

time

selectionthreshold

e l e c t i o n

election*

eclipse

elapse electricity

elect

The activation-selection model can be captured through parallel activation of competitors, each of which receives activation based on how well the signal matches.

As information is received that indicates a bad match, their activation will decay.

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Cross-Modal Priming: Experimentally verifying the existence of candidate sets

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Cross-modal priming: For literate adults with typical hearing, there are two modes or modalities for language comprehension: auditory and visual.

Cross-modal priming takes advantage of the existence of these two modalities by using both in a priming paradigm: the prime will be in one modality, the target will be in the other.

The general idea is that using two modalities allows two distinct stimuli to be presented simultaneously, without concerns that one will be masked by the other.

.........................................DOG.......................prime:

target: CATThe visual presentation of the target is timed to a specific point in the auditory presentation of the prime!

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Lets develop an experiment to test for the existence of candidate sets

.........................................KISS.......................prime:

SHIPtarget:There is no phonetic relationship and no semantic relationship between KISS and SHIP, so the reaction time should be normal.

normal reaction time

.........................................CAPT.......................prime:

SHIPtarget:If candidate sets are real, CAPT will activate CAPTAIN, which in turn will semantically activate SHIP through spreading activation!

faster reaction time

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From an activation perspective

* SHIP

activ

atio

n

timeKISS

No relationship: neither phonetic nor semantic

* SHIPac

tivat

ion

timeCAPT

capta

in

ship

Candidate activation of captain through phonetic relationship, followed by semantic priming of ship through a semantic relationship

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Lets develop an experiment to test for the existence of candidate sets

.........................................KISS.......................prime:

GUARDtarget:There is no phonetic relationship and no semantic relationship between KISS and GUARD, so the reaction time should be normal.

normal reaction time

.........................................CAPT.......................prime:

GUARDtarget:If candidate sets are real, CAPT will activate CAPTIVE, which in turn will semantically activate GUARD through spreading activation!

faster reaction time

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From an activation perspective

* GUARDac

tivat

ion

time* GUARD

activ

atio

n

timeKISS CAPT

capti

ve

guard

No relationship: neither phonetic nor semantic

Candidate activation of captive through phonetic relationship, followed by semantic priming of guard through a semantic relationship

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Evidence for candidate activation through semantic priming!

* GUARD

activ

atio

n

timeCAPT

capti

ve

guard

* SHIP

activ

atio

n

timeCAPT

capta

in

ship

We can see that CAPT activates both captain and captive based on the fact that both SHIP and GUARD receive reaction time boosts from CAPT.

This only makes sense if CAPT phonetically activates a candidate set that contains both captain and captive, and then spreading semantic activation creates semantic priming of SHIP and GUARD.

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Manipulating Activation

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Phonotactic Probability Phonotactic probability: The likelihood of occurrence (probability) of a specific sequence of sounds.

Phonotactics means combination of sounds

Probability means the likelihood of occurrence

High PP words Low PP wordsbellline

pagedish

What are the possible ways that phonotactic probability could affect lexical access (either activation or selection)?

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One possibility is to liken it to the frequency effect

c a t

c a a t

We assume that the phonetic form of the word itself forms some sort of unit that is tracked by the brain (as part of lexical representation)

What if we also track sublexical units of phonetic form, such as the bigrams of the word?

If true, we could imagine that each of these sublexical units would have a resting activation level -- crucially a level that could be affected by the frequency of the sublexical units.

In other words, high phonotactic probability could lead to a higher resting activation level for the sublexical units, which might translate into facilitation of the activation stage.

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So Phonotactic Probability will facilitate activation

bell page

activ

atio

n

time

activ

atio

n

time

Higher PP words will have higher resting activation levels for their subunitsLower P words will have lower resting activation levels for their subunits

be ll pa ge

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Manipulating Selection

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Perceptual ConfusabilitySome examples:

Madonna - La Isla Bonita

What some people hear: Last night I dreamt of some bagels

What is really said:Last night I dreamt ofSan Pedro

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Perceptual ConfusabilitySome examples:

Nirvana - Smells Like Teen Spirit

What some people hear: Here we are now in containers

What is really said:Here we are now, entertain us

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The candidate set

p kt f s ht m l

b gd v z d n rw

y a i e ou

election

avow abuse eclipse eschew

electricity elect elector electorate

elated elapse ellipse elastic

l k nelection

The candidate set is the set of words that are phonetically similar to the target word, and therefore are activated during the activation phase.

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Neighborhood Density: a measure of the size of the candidate set

trap

trappertrapsstrap

craptrack

taprap

trip

Neighborhood Density is a measure of the number of perceptual competitors of a target word. Neighborhood Density = number of words that can be created by adding, changing, or deleting a sound

add a sound:

change a sound:

delete a sound:

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Neighborhood Density and Selection

competitorcompetitor

competitorword 1

competitorcompetitor

competitor

competitor

competitor

competitor

competitor

competitor competitor

competitorword 2competitor

Which word will be selected faster?

This one, because it has fewer competitors, so selection is easier.

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Testing these predictions

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Phonotactic Probability and Neighborhood Density

One thing to note about phonotactic probability and neighborhood density is that they tend to correlate: words that are high or low in one will also be high or low in the other:

High PP/ND words Low PP/ND wordsbellline

pagedish

This is not a necessary fact: one could imagine a very frequent word that has no neighbors, but its high frequency makes the phonotactic probability of its constituent sound sequences high.

One could also imagine a neighborhood of words that are all very low frequency, resulting in low phonotactic probability for those sound sequences.

But in general, high ND and high PP correlate.

This makes some sense: if there are a high number of words (high ND) that have similar sounds, then those sounds will probably be relatively frequent (because there are a lot of words that will contain those sounds).

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Phonotactic Probability and Neighborhood Density

High Phonotactic Probability facilitates activation

time

time

activation selection

activationstart

start

selection

High Neighborhood Density inhibits selection

Low Phonotactic Probability inhibits activation

Low Neighborhood Density facilitates selection

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Looking for behavioral effects

Vitevitch and Luce 1999 created two lists of words, one with high neighborhood density and one with low neighborhood density

High PP/ND words Low PP/ND wordsbellline

pagedish

They then used these lists to investigate the effect of neighborhood density on words and nonwords...

High ND nonwords Low ND nonwordsmidepake

jizeyush

They then created similar lists of nonwords, which are strings of sounds that would be legal words in English, but just dont exist:

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Lexical DecisionThe first thing we can look at is what happens in a standard lexical decision task where participants are asked to indicate whether a string is a word or not:

The bars represent reaction times.

Vitevitch and Luce found that high PP/ND inhibited recognition (slowed down RTs) for both words and non-words

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The inhibition suggests that selection was impacted for WORDS

competitorcompetitor

competitorword 1

competitorcompetitor

competitor

competitor

competitor

competitor

competitor

competitor competitor

competitorword 2competitor

Weve already seen how it is that neighborhood density slows down word recognition.

Fewer competitors in the candidate set means faster selection time!

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But what about non-words?

competitorcompetitor

competitornonword 1

competitorcompetitor

competitor

competitor

competitor

competitor

competitor

competitor competitor

competitornonword 2competitor

The competitors of non-words are real words!

In order to decide that a nonword is not a word, you must exclude all of the competitors!

So fewer is faster.29

The Matching Task

But they found that high PP/ND inhibited decisions (slowed down RTs) of words.

Vitevitch and Luce also looked at what happens in a matching task where participants are asked to indicate whether two strings are the same or not:

They found that high PP/ND facilitated decisions (decreased RTs) of nonwords.

How do we explain these divergent results?

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Selection always occurs for wordsVitevitch and Luce take this as evidence that the process of selection is automatically triggered by words regardless of the task.

MatchingLexical Decision

Because selection always occurs, and because density inhibits selection, words are slower because of high ND in every task.

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Selection only occurs in lexical decision for nonwords

Vitevitch and Luce take this as evidence that the process of selection is only triggered for nonwords in a lexical decision task.

MatchingLexical Decision

In a matching task, selection is not requied, so there is no process for high ND to slow down, but high PP can still facilitate the activation stage.

selection is inhibited by high ND

activation is facilitated by high PP

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Notice that the selection effect is larger than the activation effect

High PP/ND:

time

time

activation selection

activationstart

start

selectionLow PP/ND:

The fact that we only see the inhibition of selection for high PP/ND suggests that the ND inhibition of selection is larger than the PP faciiltation of activation

This also means that we will never see the facilitation effect on words using reaction times, because selection always occurs for words.

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Electrophysiological evidence for activation and selection

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The time course of neuromagnetic responses to words

several components before the button press

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Identifying a component that tracks lexical access

Embick et al. 2000 identified several MEG components that occurred prior to the response in a lexical decision experiment.

They then used the following logic to determine which component tracks lexical access: lexical access varies with frequency, therefore an MEG component that tracks lexical access should vary with frequency.

So they created six lists of words that had substantially different frequencies (counted as utterances per million in a corpus).

And then used those six lists in a lexical decision experiment while simultaneously recording MEG.

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The M350 latency tracks frequencyAs expected, Embick et al. found that reaction times to higher frequency words were faster, and lower frequency words were slower.

The only component whose latency tracked the RT latency was the M350, suggesting that the M350 tracks lexical access.

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The M350 tracks lexical access, but which stage?

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The M350 tracks lexical access, but which stage?

High Phonotactic Probability facilitates activation

activation selection

High Neighborhood Density inhibits selection

We can use the effect of Phonotactic Probability/Neighborhood Density on the M350 to determine which process the M350 tracks. The direction that its latency moves will tell us which process!

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Pylkkanen et al. 2002Pylkkanen et al. used the same materials as Vitevitch and Luce 1999, and ran a lexical decision task while simultaneously recording MEG.

The RTs to both words and nonwords show an inhibition of selection by high neighborhood density.

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Pylkkanen et al. 2002Pylkkanen et al. used the same materials as Vitevitch and Luce 1999, and ran a lexical decision task while simultaneously recording MEG.

But the M350 shows a facilitation of activation for both words and nonwords!

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Pylkkanen et al. 2002

words nonwords

We can see this facilitation effect in the waveforms of the MEG too:

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The M350 appears to track activation

High Phonotactic Probability facilitates activation

activation selection

High Neighborhood Density inhibits selection

We should note that prior to this, there was no way to see the facilitation effect of phonotactic probability on the activation stage of words because the inhibition effect of neighborhood density on selection would always interfere!

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