Computational Psycholinguistics Lecture 8: Lexical Processing

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Computational Psycholinguistics

Lecture 8: Lexical Processing

Andrea Weber

[email protected]

Computerlinguistik

Universität des Saarlandes

© Andrea Weber Computational Psycholinguistics 2

Literature

Lively, S., Pisoni, D., & Goldinger, S. (1994). Spoken word recognition:Research and theory. In M.A. Gernsbacher (Ed.), Handbook ofPsycholinguistics. Chapter 8, pp.265-301.San Diego: Academic Press. Either library or my office (no electronic version)

Tanenhaus, M., Spivey-Knowlton, M., Eberhard & Sedivy, J. (1996).Using eye movements to study spoken language comprehension:evidence for visually mediated incremental interpretation. In T. Inui & J.McClelland (Eds.), Attention & Performance XVI: Integration inperception and communication (pp. 457-478). Cambridge, MA: MITPress. My office (no electronic version); this is the extended version of the 1995

Science paper

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Overview next two lectures

This week:

What is lexical processing

What are the stages of lexical processing

What influences the process of spoken-word recognition

How eye tracking came into play

Some things we learned about lexical access since 1995


Overview next two lectures

Next week:

Short summary of last week

Models of word recognition

..... switching lecturers....

The role of morphology in word recognition

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Lexical processing

Lexical processing is the means by which single words are recognized People do it very fast

Average person has around 50,000 words in memory Takes only 250 msec to find a word from among 50,000

It is automatic and robust

Word recognition is a retrieval task, not compositional like sentenceprocessing

The auditory or visual signal must be mapped onto representations ofknown words in the listener’s mental lexicon

Sounds relatively simple, but words are not highly distinctive (tens ofthousands of words are constructed from 30 to 40 phonemes)


How do listeners know when to recognize a word?

steak

stack

state

snake

stay

take

ache

mistakefirst acre

Words tend to resemble other words

Words may have other words embedded within them…

Or be themselves embedded in longer sequences

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Differences between written and spoken words

Spoken word recognition takes place in time - words are not heard all at oncebut from beginning to end.

Written words are available to readers as a whole (depending on length).

Typically there is no chance to reconsider the spoken input.

In printed text we typically can re-read words or passages.

Spoken words are rarely heard in isolation but rather within longer utterances,but there is no reliable cue in speech to mark word boundaries.

In printed text white space unambiguously mark word beginnings.

In spoken words phonemes are realized differently in different contexts(coarticulation). “Sweet girl” is often pronounced as “sweek girl” (but also withinsyllables -> compare tongue position with /ki/ versus /ku/).

No such variability is usually found in printed text.


Stages of lexical processing

Initial contact

First contact with the lexicon after hearing some speech

Different theories assume different forms of contact Spectrographic (LAFS (lexical access from speech) model assumes direct

lexical access); frequency/speed at which air particles vibrate plusintensity/loudness in a sound wave form pattern that is recognizable by thelexicon

Motor theory assumes the extraction of articulatory gestures (i.e., lip rounding,tongue position); brain constructs a model of intended articulatory movements

Phonemic theories (or bigger units such as the syllable) assume a prelexicalrepresentation level

Causes certain lexical representation to “activate”

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Lexical selection Activation continues to accumulate (or die off)

Type of activation depends on the model being considered All-or-nothing activation

Better fit leads to higher degrees of activation

Maybe affected by the properties of the words, such as frequency

Pool of possible candidates being considered changes over time



Word recognition End point of selection phase

Is reached when only a single candidate remains in the pool

Is a process of competition

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Lexical access and integration

Lexical access: point at which lexically-stored information (phonological,morphological, semantic, etc.) becomes available

Integration: working the meaning of the word into the overall meaning ofthe sentence



In sum....

Initial contact

Lexical selection

Word recognition

Lexical access and integration

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Competition in lexical processing

/s/sad

psychology

staple

snake

stay

stupid ....

/st/

staple

stay

stupid ....

/steI/

staple

stay

/steIp/

staple


Uniqueness point

“staple” could be identified by the /p/ because no other English wordswould match the string of phonemes in the mental lexicon. This point ina word is called uniqueness point. Word recognition can occur beforeall phonemes of the word are available.

However, quite regularly words do not become unique prior to wordoffset: /steI/ could not only be the word “stay”, it could also be the beginning of

“steak, stage, staple, station, state, stale, stain, stable,….”

More phonemic input is needed to identify “stay”:/steIku/ is not a word, also there is no English word beginning with /u/, thusthere must be a word boundary between /I/ and /k/ (stay cool)

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In general: the more word candidates match the incoming speechsignal, the more competition there is and the slower recognitionproceeds.

Furthermore, we not only find parallel activation of candidates thatmatch in onset (beaker-beetle), but also in rhyme (beaker-speaker)

Importantly, word candidates can get activated by any part of thespeech input, not just the onset (embedding)

Competition in lexical processing


Competition (more realistic)

/s/sad

psychology

staple

snake

stay

stupid ....

/st/

tape

staple

tiger

stay

stupid ....

/steI/apron

tape

staple

stay

/steIp/

apron

tape

staple

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What influences lexical processing

Now that we know about the stages of lexical processing we will findout which factors have an influence on the speed/smoothness of lexicalprocessing

Paradigms that are frequently used to investigate lexical processing Lexical decision

Word spotting

Eye tracking


Press the button when the following item is an existing word:

We measure response time and error rate

Fast response = easy access 400 ms Slow response = hard access 500 ms

Lexical decisionLexical decision

housenolkballverdictbeefttronk

this includes the time it takes to makethe decision to press the button, planthe finger movement, and execute thebutton press

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1. Word Length long words = asparagus

short words = eye

What affects lexical access time?What affects lexical access time?

short words get faster responses than long words E.g. eye vs. asparagus

Note that this effect is caused by the “spreading” of words intime (or space) and is not influenced by the structure of themental lexicon.


2. Uniqueness point early uniqueness point = strawberry (there are no other English words

beginning with /strç˘b/

late uniqueness point = blackberry (not unique at /b/ of berry; blackbird,blackbeetle,…)


Faster responses to words with earlier uniqueness points E.g. strawberry vs. blackberry

Marslen-Wilson,W. (1990). Activation, competition, and frequency in lexicalaccess. In G. Altmann (Ed.), Cognitive Models of speech processing, pp.148-172. Cambridge: MIT Press.

Again, this effect does not necessarily tell us anything about theorganization of the mental lexicon.

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3. Word Frequency

High frequency words = common words (“cat, mother, house”)

Low frequency words = uncommon words (“accordion, compass”)


High frequency words are faster to access than low frequency words even when they’re balanced on other features (e.g. length)

E.g. pen vs. pun

Marslen-Wilson,W. (1990). Activation, competition, and frequency in lexicalaccess. In G. Altmann (Ed.), Cognitive Models of speech processing, pp.148-172. Cambridge: MIT Press.



4. Neighbourhood effects Shown by Luce, P., Pisoni, D., & Goldinger, S. (1990).

Similarity neighbourhoods of spoken words. In G. Altmann(Ed.), Cognitive Models of Speech Processing, Cambridge,MA: MIT Press, pp. 122-147.

But not found by Marslen-Wilson (1990).

yacht peach

FAST

SLOW … because peachhas lots of high-

frequencyneighbours (e.g.

reach, peace,beach, pea)

Both high-frequency

High frequency words with few, low-frequencyneighbours are most easily recognized

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words related in sound (not meaning)prime target

book dale

tale dale

SLOW

FAST … because dale isalready ‘warmed

up’ by having justactivated tale

5. Phonological (sound) Priming

In priming studies the actual target word is preceded by thepresentation of a prime word, the prime word can be related to thetarget in different ways

Slowiaczek, L. & Hamburger, M. (1992). Prelexical facilitation andlexical interference in auditory word recognition. Journal ofExperimental Psychology: Learning, Memory and Cognition, 18,1239-1250.



Subject sees 2 words

Must say YES or NO whether both are real words

doctor grass

doctor nurseSLOWFAST … because nurse

is already‘warmed up’ by

having justactivated doctor

6. Semantic Priming

Meyer, D.E., & Schvaneveldt, R.W. (1971). Facilitation in recognizingpairs of words: Evidence of a dependence between retrieval operations.Journal of Experimental Psychology, 90, 227-234.


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7. Concreteness Kroll, J. F. & Merves, J. S. (1986). Lexical access for concrete and abstract

words. J Exper Psych: Learning, Memory & Cognition, 12(1):92--107

apple

anger

FAST

SLOW … because appleis more concrete

(and less abstract)than anger

Both high-frequency


In sum, ...

Factors influencing lexical processing:

Word length

Uniqueness point

Word frequency

Neighborhood size

Phonological priming

Semantic priming

Concreteness

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Word spotting

Press the button when you spot an existing word in a nonsensesequence, then say the word aloud.

We measure again response time and error rate.

/d´mEs/ /n´mEs/

/sQkr´f/ /sQkr´k/

With this paradigm the competition effect has been demonstrated (e.g.,McQueen, Norris, & Cutler, 1994).

… activation of ‘domestic’makes it harder to spot‘mess’, no English wordbegins ‘nomes…’, thus‘mess’ is easier to spot

… activation of ‘sacrifice’makes it harder to spot‘sack’

‚mess‘ embedded

‚sack‘ embedded

slow

fast

slow

fast


And then came Tanenhaus....

Even though both lexical decision and word spotting are considered onlineparadigms, in both cases measurements are taken after the complete wordshave been presented.

The presentation of nonsense sequences might not be considered totallynatural.

Reaction time measurements do not tell us much about the time course ofprocessing.

Eye-tracking offers the possibility to investigate processes during actual wordrecognition.

Tanenhaus, M., Spivey-Knowlton, M., Eberhard, K., & Sedivy, J. (1995).Integration of visual and linguistic information in spoken languagecomprehension. Science, 268, 1632-1634.

See also Tanenhaus, M., Spivey-Knowlton, M., Eberhard & Sedivy, J. (1996).Using eye movements to study spoken language comprehension: evidence forvisually mediated incremental interpretation. In T. Inui & J. McClelland (Eds.),Attention & Performance XVI: Integration in perception and communication (pp.457-478). Cambridge, MA: MIT Press.

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Example Tanenhaus (1995)

Click on the candy.

target: candy

competitor: candle

distractors: strawberry, dice


Example Tanenhaus (1995)

Click on the candy.

target: candy

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Results Tanenhaus

Tanenhaus and colleagues used a video-based eye tracker (33 mssampling rate).

They analyzed the movie from target word onset until target wordoffset.

They measured the onset time of the first saccade to the target object.

400

420

440

460

480

500

520

540

mit Kompetitor ohne Kompetitor

Eye movements are tightly locked in time with the spoken utterance and thus caninform us about the ongoing comprehension process

Retrieving lexical information begins prior to word offset (it takes about 200 ms tolaunch a programmed eye movement)

The names of possible referents in the display influenced the speed of wordrecognition (this argues for an incremental interpretation of the speech signal incombination with visual information)


Fixations over time

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What happened since then?

First, it was important to show, that results are not task-specific and arenot simply caused by visual presentation of the four objects (is theobserved competition effect reflecting competition in real life)

Distract from phonological overlap

Results don’t change when pictures are repeatedly shown

Participants, when asked, are not aware of phonological overlap


What happened since then?

But more importantly, it has been shown that fixations are influencedby properties of the language system (this would not be the case if theresults just reflect participants using strategies, by-passing the normalspeech comprehension system)

For instance, effects of lexical frequency were replicated (Dahan,Magnuson, & Tanenhaus, 2001) We know about frequency effects from other paradigms (high frequent

words are faster recognized than low frequent words)

Using eye tracking, it was shown that high frequent competitors are fixatedmore often and earlier than low frequent competitors

Also, the time course and probabilities of eye movements closelycorrespond to response probabilities derived from TRACE simulations(Allopenna, Magnuson, & Tanenhaus, 1998)

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Lexikal frequency, Dahan et al. (2001)

„Click on the bench“

target

bench (low frequ.)

competitor

bell (low frequ.)

competitor

bed (high frequ.)


Allopenna et al. (1998)

Computationally implemented models of spoken-word recognition exist(e.g., TRACE, Shortlist)

Such models, are based on ample empirical results and can be used tosimulate and predict (quantitatively) human behavior during spoken-word recognition

TRACE was used to calculate predictions of response probabilities fora certain set of items

The same items were presented to participants during an eye-trackingstudy

onset competitor

beetletarget

beaker

rhyme competitor

speaker

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The close match between predicted and observed fixation patternsallowed the following linking hypothesis (link between lexical activationand eye movements):

The activation of the name of a picture determines the probability that asubject will shift attention to that picture and thus make a saccadic eyemovement to fixate it.

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Summary

What is lexical processing The means by which words are being recognized

What are the stages of lexical processing Initial contact, lexical selection, word recognition, lexical access and integration

What influences the process of spoken-word recognition Length, uniqueness point, frequency, neighborhood, phonological and semantic

priming, concreteness

How eye tracking came into play validating the paradigm by replicating competition and frequency effects,

establishing a strong linking hypothesis

Some things we learned about lexical access since 1995 Rhyme competition, subcategorical influences, morphosyntactic constraints,

semantic field, verb information, prosody, ….

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Computational Psycholinguistics Lecture 8: Lexical Processing