Lexical Access: Generation & Selection
Jan 08, 2016
Lexical Access:Generation & Selection
Today’s Main Topic
• Listeners as active participants in comprehension process
• Model system: word recognition
Outline
1. Speed & Robustness of Lexical Access
2. Active Search
3. Evidence for Stages of Lexical Access
4. Autonomy & Interaction
Outline
1. Speed & Robustness of Lexical Access
2. Active Search
3. Evidence for Stages of Lexical Access
4. Autonomy & Interaction
How do we recognize words?
The mental lexicon
sport figure
sing door carry
turf turtle gold turk turkey
turn
water turbo turquoise
turnip turmoil
How do we recognize words?
• The Simplest Theory
– Take a string of letters/phonemes/syllables, match to word in the mental lexicon
– (That’s roughly how word processors work)
• …is it plausible?
Word Recognition is Fast
• Intuitively immediate - words are recognized before end of word is reached
• Speech shadowing at very brief time-lags, ~250ms (Marslen-Wilson 1973, 1975)
Lexical Access is Robust
• Succeeds in connected speech
• Succeeds in fast speech
• Survives masking effects of morphological affixation and phonological processes
• Deleted or substituted segments
• Speech embedded in noise
But…
• Speed and robustness depends on words in context
sentence --> word context effects
• In isolation, word recognition is slower and a good deal more fragile, susceptible to error
• …but still does not require perfect matching
Questions
• How does lexical access proceed out of context?
• Why is lexical access fast and robust in context?
• When does context affect lexical access?
– does it affect early generation (lookup) processes?
– does it affect later selection processes?
Additional Context Effects
• Word context affects phoneme identification…
word --> phoneme context effects
Phoneme Restoration
• The _eel had a broken axleThe _eel on the orange was hard to cut(Warren 1970)
• Phoneme restoration effects are stronger(i) in words than non-words(ii) later in words(iii) in strongly biasing contexts
Phoneme Monitoring
• press the button as soon as you hear a ‘b’
• “in the yard was a large group of twittering birds”
“cat, dog, horse, rabbit …”
• Monitoring is facilitated by context
Perceptual Boundaries
Perceptual Boundaries
DA TA
Perceptual Boundaries
DASK TASK
(Ganong 1980)
Perceptual Boundaries
DASK TASK
(Ganong 1980)
Perceptual Boundaries
DASH TASH
(Ganong 1980)
Perceptual Boundaries
DASH TASH
(Ganong 1980)
Classic Experimental Paradigms
Accessing the Mental Dictionary
Reaction Time Paradigms
• Lexical Decision
• Priming
Looking for Words
• List 1sicklecathartictorridgregariousoxymoronatrophy
• List 2parabolaperiodontistpreternaturalpariahpersimmonporous
Looking for Words
• List 1sicklecathartictorridgregariousoxymoronatrophy
• List 2parabolaperiodontistpreternaturalpariahpersimmonporous
Speed of look-up reflects organization of dictionary
Looking for Words
+
Looking for Words
DASH
Looking for Words
+
Looking for Words
RASK
Looking for Words
+
Looking for Words
CURLY
Looking for Words
+
Looking for Words
PURCE
Looking for Words
+
Looking for Words
WINDOW
Looking for Words
+
Looking for Words
DULIP
Looking for Words
+
Looking for Words
LURID
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
Looking for Words
+
Looking for Words
PRESSULE
Looking for Words
+
Looking for Words
DOCTOR
Looking for Words
+
Looking for Words
NURSE
Looking for Words
• Semantically Related Word Pairsdoctor nursehand fingerspeak talksound volumebook volume
Looking for Words
• In a lexical decision task, responses are faster when a word is preceded by a semantically related word
• DOCTOR primes NURSE
• Implies semantic organization of dictionary
Outline
1. Speed & Robustness of Lexical Access
2. Active Search
3. Evidence for Stages of Lexical Access
4. Autonomy & Interaction
Active Recognition
• System actively seeks matches to input - does not wait for complete match
Cost of Active Search…
• Many inappropriate words activated
• Inappropriate choices must be rejected
• Two Stages of Lexical Accessactivation vs. competitionrecognition vs. selectionproposal vs. disposal
Cohort
S
song
story
sparrow
saunter
slow
secret
sentry
etc.
Cohort
SP
spice
spoke
spare
spin
splendid
spelling
spread
etc.
Cohort
SPI
spit
spigot
spill
spiffy
spinaker
spirit
spin
etc.
Cohort
SPIN
spin
spinach
spinster
spinaker
spindle
Cohort
SPINA spinach
Cohort
SPINA spinach
word uniqueness point
Cohort
SPINAspinach
spinet
spineret
Evidence for Cohort Activation
KAPITEIN KAPITAAL
(Marslen-Wilson, Zwitserlood)
Evidence for Cohort Activation
KAPITEIN KAPITAAL
KAPIT…
(Marslen-Wilson, Zwitserlood)
Evidence for Cohort Activation
KAPITEIN KAPITAAL
KAPIT…
BOOT
GELD
(Marslen-Wilson, Zwitserlood)
Evidence for Cohort Activation
KAPITEIN KAPITAAL
KAPIT…
BOOT
GELD
(Marslen-Wilson, Zwitserlood)
Evidence for Cohort Activation
KAPITEIN KAPITAAL
KAPIT…
BOOT
GELD
KAPITEIN
BOOT
GELD
(Marslen-Wilson, Zwitserlood)
Cohort Model
• Partial words display priming properties of multiple completions: motivates multiple, continuous access
• Marslen-Wilson’s claims
– Activation of candidates is autonomous, based on cohort only
– Selection is non-autonomous, can use contextual info.
• How to capture facilitatory effect of context…
Gating Measures
• Presentation of successive parts of words
– S
– SP
– SPI
– SPIN
– SPINA…
• Average recognition times
– Out of context: 300-350ms
– In context: 200ms(Grosjean 1980, etc.)
Word Monitoring
• Listening to sentences - monitoring for specific words
– Mean RT ~240ms
– Identification estimate ~200ms
• Listening to same words in isolation
– Identification estimate ~300ms
(Brown, Marslen-Wilson, & Tyler)
Cross-Modal Priming
Cross-Modal Priming
The guests drank vodka, sherry and port at the reception
(Swinney 1979, Seidenberg et al. 1979)
Cross-Modal Priming
The guests drank vodka, sherry and port at the reception
WINE
SHIP
(Swinney 1979, Seidenberg et al. 1979)
Cross-Modal Priming
The guests drank vodka, sherry and port at the reception
WINE
SHIP
(Swinney 1979, Seidenberg et al. 1979)
Cross-Modal Priming
The guests drank vodka, sherry and port at the reception
WINE
SHIP
(Swinney 1979, Seidenberg et al. 1979)
Cross-Modal Priming
The guests drank vodka, sherry and port at the reception
WINE
SHIP
(Swinney 1979, Seidenberg et al. 1979)
Cross-modal Priming
• Early: multiple access
• Late: single access
…i.e., delayed effect of context
CMLP - Qualifications
• Multiple access observed– when both meanings have roughly even frequency
– when context favors the lower frequency meaning
• Selective access observed– when strongly dominant meaning is favored by context
(see Simspon 1994 for review)
Why multiple/selective access?
• How could context prevent a non-supported meaning from being accessed at all?
(Note: this is different from the question of how the unsupported meaning is suppressed once activated)
• Possible answer: selective access can only occur in situations where context is so strong that it pre-activates the target word/meaning
Cohort Model
• Partial words display priming properties of multiple completions: motivates multiple, continuous access
• Marslen-Wilson’s claims
– Activation of candidates is autonomous, based on cohort only
– Selection is non-autonomous, can use contextual info.
• How to capture facilitatory effect of context…
Cohort
SPINA spinach
Cohort
SPIN
spin
spinach
spinster
spinaker
spindle
Speed of Integration
• If context can only be used to choose among candidates generated by cohort…
– context can choose among candidates prior to uniqueness point
– but selection must be really quick, in order to confer an advantage over bottom-up information
• Summary of cohort story• Single/multiple access (Simpson)
– Context & dominant/subordinate frequency (Rayner & Frazier)– Types of context (Tabossi)
• Electrophysiological Evidence– M350, distinguishing access from selection/competition– Suggestions about N1, etc.
• Eye-tracking– continuous activation - TRACE– frequency - Dahan et al.
• Priority for category or morphological information, decomposition– Vannest & Boland
Refining the Story
• Frequency in context– eye-tracking in reading
– eye-tracking and object recognition
• Electrophysiological measures of multiple access
• When can context affect generation?– strongly supporting contexts
– ERP evidence
Evidence for Cohort Activation
CAPTAIN CAPTIVE
CAPT…
SHIP
GUARD
CAPTAIN
SHIP
GUARD
(Marslen-Wilson, Zwitserlood)
Frequency in Reading
• Rayner & Frazier (1989): Eye-tracking in reading
– measuring fixation durations in fluent reading
– ambiguous words read more slowly than unambiguous, when frequencies are balanced, and context is unbiased
– unbalanced words: reading profile like unambiguous words
– when prior context biases one meaning• dominant-biased: no slowdown due to ambiguity
• subordinate-biased: slowdown due to ambiguity
• contextual bias can offset the effect of frequency bias
– how can context boost the accessibility of a subordinate meaning?
Frequency in Object Recognition
X
bench
bed
bell
lobster
“Pick up the be..” (Dahan, Magnuson, & Tanenhaus, 2001)
Frequency in Object Recognition
• Timing estimates
– Saccadic eye-movements take 150-180ms to program
– Word recognition times estimated as eye-movement times minus ~200ms
Frequency in Object Recognition
(Dahan, Magnuson, & Tanenhaus, 2001)
Frequency in Object Recognition
(Dahan, Magnuson, & Tanenhaus, 2001)
Frequency in Object Recognition
(Dahan, Magnuson, & Tanenhaus, 2001)
Evidence for Cohort Activation
CAPTAIN CAPTIVE
CAPT…
SHIP
GUARD
CAPTAIN
SHIP
GUARD
(Marslen-Wilson, Zwitserlood)
Matches to other parts of words
• Word-ending matches don’t prime
– honing [honey] bij [bee]woning [apartment]foning [--]
Disagreements
– Continuous activation, not limited to cohort, as in TRACE model (McClelland & Elman, 1986)
– Predicts activation of non-cohort members, e.g. shigarette, bleasant
Non-Cohort Competitors
(Allopenna, Magnuson, & Tanenhaus, 1998)
“Pick up the…”
beaker
beetle (onset)speaker (non-onset)carriage (distractor)
Non-Cohort Competitors
(Allopenna, Magnuson, & Tanenhaus, 1998)
“Pick up the…”
beaker
beetle (onset)speaker (non-onset)carriage (distractor)
Outline
1. Speed & Robustness of Lexical Access
2. Active Search
3. Evidence for Stages of Lexical Access
4. Autonomy & Interaction
M350
(based on research by Alec Marantz, Liina Pylkkänen, Martin Hackl & others)
Lexical access involves
1. Activation of lexical representations• including activation of representations
matching the input, and• lateral inhibition between activated
representations
2. Followed by selection or decision• involving competition among activated
representations that are similar in form
The mental lexicon
sport figure
sing door carry
turf turtle gold turk turkey
turn
water turbo turquoise
turnip turmoil
The mental lexicon
sport figure
sing door carry
turf turtle gold turk turkey
turn
water turbo turquoise
turnip turmoil TURN
Automatic activation
TURN
sport figure
sing door carry
turf turtle gold
turk turkey
water turn
turbo turquoiseturnip turmoil
Lateral inhibition
TURN
sport figure
sing door carry
turf turtle gold
turk turkey
water turn turbo turquoise
turnip turmoil
What is lexical access?
time
leve
l of
activ
atio
n
resting level
TURN
Stimulus: TURN
TURNIP
TURFTURTLE
Activation Competition Selection/Recognition
(e.g. Luce et al. 1990, Norris 1994)
RESPONSE TO A VISUAL WORD Sagittal view
A P
M350
M350
0 200 300 400 Time [msec]
MEG response components elicited by visually presented words in the lexical decision task
RMS analysis of component field patterns.
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 2 3 4 5 6
Frequency Category (Frequent -- Infrequent)
Latency of m350 Component
Categories (n/Million):
1: 7002: 1403: 30 4: 6 5: 1 6: .2
Neighbors & Competitors
• Phonotactic probability– sound combinations that are likely in English– e.g. ride vs. gush
• Neighborhood density– number of words with similar sounds– ride, bide, sighed, rile, raid, guide, died, tried,
hide, bride, rise, read, road, rhyme, etc.– gush, lush, rush, gut, gull …
RT
Behavioral evidence for dual effects
• Same/different task (“low-level”) RTs to nonwords with a high phonotactic probability are speeded up.
• Lexical decision task (“high-level”)RTs to nonwords with a high phonotactic probability are slowed down!
High probability: MIDE
YUSH RT
RT MIDE
YUSH RT
Low probability:
High probability:
Low probability:
Sublexicalfrequency effect
(Vitevich and Luce 1997,1999)
Competition effect
Stimuli
High probability Low probability
Word BELL, LINE PAGE, DISH
Nonword MIDE, PAKE JIZE, YUSH
• Materials of Vitevich and Luce 1999 converted into orthographic stimuli.
• Four categories of 70 stimuli:
• High and low density words frequency matched.
(Pylkkänen, Stringfellow, Marantz, Brain and Language, in press)
Effect of probability/density (words)
100
200
300
400
500
600
700
M170 M250 M350 RT
HighProbWord LowProbWord
n.s.
n.s.
**
*
(Pylkkänen, Stringfellow, Marantz, Brain and Language, in press)
Effect of probability/density (nonwords)
0
100
200
300
400
500
600
700
800
M170 M250 M350 RT
HighProbNonword LowProbNonword
n.s.n.s.
*
**
(Pylkkänen, Stringfellow, Marantz, Brain and Language, in press)
M350 = 1st component sensitive to lexical factors but not affected by competition
time
leve
l of
activ
atio
n
resting level
TURN
TURNIP
TURFTURTLE
Activation Competition Selection/RecognitionM350
Stimulus: TURN
Outline
1. Speed & Robustness of Lexical Access
2. Active Search
3. Evidence for Stages of Lexical Access
4. Autonomy & Interaction
Autonomy
• “…a system [is] autonomous by being encapsulated, by not having access to facts that other systems know about” (Fodor 1983)
• “Autonomy would imply that processing operations at a given level proceed in the same way irrespective of whatever counsel might be deducible from the higher-level considerations” (Boland & Cutler)
Model Implied So Far
• Stage 1: activation based upon cohortsno effect of context at this stage
• Stage 2:selection affected by context
Boland & Cutler
• The debate over interaction/autonomy in lexical access focuses on the generation (activation) stage
• There is broad agreement that context affects lexical choices once multiple candidates have been generated
Cross-Modal Priming
The guests drank vodka, sherry and port at the reception
WINE
SHIP
(Swinney 1979, Seidenberg et al. 1979)
Cross-Modal Priming
The guests drank vodka, sherry and port at the reception
WINE
SHIP
(Swinney 1979, Seidenberg et al. 1979)
Cross-Modal Priming
• How could context prevent a contextually unsupported meaning from being accessed?
Cross-Modal Priming
• Conflicting results over effect of context on multiple access
• Tabossi (1998)
– The violent hurricane did not damage the ships which were in the port, one of the best equipped along the coast.
– Contexts are highly constraining, prime a specific feature of the target meaning.
Active Comprehension
• Distinction between activation and selection applies equally to syntactic comprehension
• Is active comprehension a fully general property of language understanding?
N400
Negative polarity peaking at around 400 ms central scalp distribution
(Kutas & Federmaier 2000)
(Kutas & Federmaier 2000)
‘baseball’ is not at all plausible here, yet it elicits a smaller N400 - why?
Input to left hem. visual system must have privileged access to information about predictions.
Implications
• If Kutas & Federmaier’s results are robust, this implies that
– lexical priming can cause apparentearly context effects
– this implies ‘very active search’
– hemispheres are not alike in this regard
Conclusion…
• Word recognition is fast and robust because of use of context
• Speed/robustness is achieved by– active generation of candidates from incomplete input
– selection among candidates, based upon context
• Activation ˜ autonomousSelection ˜interactive
Next…
• Syntax
– most issues seen here also apply to syntactic processes
– generation stage is much more complex, since syntactic processing is more than just a lookup/activation process.