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Computational Psycholinguistics
Lecture 8: Lexical Processing
Andrea Weber
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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© Andrea Weber Computational Psycholinguistics 3
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
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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)
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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.
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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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Stages of lexical processing
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
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Stages of lexical processing
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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Stages of lexical processing
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
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Stages of lexical processing
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
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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
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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
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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.
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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,…)
What affects lexical access time?What affects lexical access time?
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”)
What affects lexical access time?What affects lexical access time?
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.
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What affects lexical access time?What affects lexical access time?
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.
What affects lexical access time?What affects lexical access time?
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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.
What affects lexical access time?What affects lexical access time?
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What affects lexical access time?What affects lexical access time?
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
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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
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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
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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)
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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
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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.)
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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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Allopenna et al. (1998)
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Allopenna et al. (1998)
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, ….