Transcript Lexical Ambiguity Resolution Lecture

Semantic Priming
(Phenomenon & Tool)
...
arm
kitchen
tree
Related prime >doctor
nurse
floor
...
<Target>
...
arm
kitchen
tree
actor < Unrelated prime
nurse
floor
...
• In a priming experiment:
– Some people see nurse immediately after doctor in a list of words
= Related condition
– Others see nurse after an unrelated word like actor
= Unrelated condition
- Notice that target word is identical across conditions, so important word
properties like frequency & length are perfectly controlled
– People respond faster, on average, in Related condition
= Priming (= facilitation)
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Lexical Ambiguity Resolution
• Many words have multiple meanings
– plant, bank, bug, deck, ...
• Ambiguous words occur far more often than we realize
• We're so good at figuring out which meaning is intended
that we rarely notice any ambiguity
– How do we do it?
– Do we retrieve multiple meanings as part of recognizing the
word, & then pick the right meaning for the context?
• Multiple Access (= Modular)
• Or does context act to prevent us from ever even
retrieving the irrelevant meaning?
• Selective Access (= Interactive)
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Semantic Priming with Ambiguous Words
...
arm
window
book
bug
spy
car
...
Ambiguous prime
Related
Targets
•
...
arm
window
book
bug
ant
car
...
...
arm
window
book
bug
sew
car
...
Unrelated
Target
In word lists, both related targets show facilitation
– Notice, in this design, it’s the prime that stays constant across conditions &
the target that differs
• Have to work hard to control properties of target that affect RT
•
What happens in sentences where it’s clear which meaning is intended?
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• Notice there’s a clever trick here
– Use a prime that has some kind of uncertainty about it
• Could be visually degraded
• Or lexically ambiguous
– Use targets related to different possible interpretations of prime
• If the response to a target is facilitated
• then the interpretation of the prime related to that target must have
been “active”
– So, using response to target to figure out how prime processed
– Can vary time lag between prime & target to tap into prime
processing at different points
= Stimulus Onset Asynchrony (SOA)
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Swinney (1979)
• Cross-modal priming study
• Primes = auditory sentence containing critical prime word
• Task = lexical decision on visual targets
• 4 kinds of auditory prime sentences:
The man was surprised when he found several ...
... insects
in the corner of the room.
... bugs
in the corner of the room.
... spiders, roaches, and other insects
in the corner of the room.
... spiders, roaches, and other bugs
in the corner of the room.
^ant
spy
sew
aln
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(contextually approp)
^ant
(contextually inapprop)
spy
(unrelated)
sew
(non-word)
aln
Psyc / Ling / Comm 525 Fall 10
Swinney (1989)
Notice, very complex design !!!
• 2 (Context vs No Context)
• x 2 (Ambiguous vs Unambiguous Prime)
• x 2 (Prime-Target SOA)
• x 4 (Target Word Type)
= 32 conditions !
– 144 participants !
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Unambiguous Conditions
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• Swinney's study is important because:
– It shows how fast things change during comprehension
– It made sense of conflicting previous results
• whether you get evidence of interaction depends on when measure
– The multiple access results are so counterintuitive!
• More recent results have modified the conclusion:
– IF one meaning of an ambiguous word is much more common
• Swinney didn’t manipulate this property of ambiguous words
– AND context strongly supports the more common meaning
– THEN, only the contextually appropriate meaning seems to be
activated
– So, when meaning frequency and context gang up, can get
selective access (Duffy, Morris, & Rayner, 1988)
• Rather than priming for a related target, they measured reading times on
ambiguous words and the words after them with an eyetracker
• Times were just as fast for ambiguous words as for unambiguous control
words if there was plenty of context supporting the more frequent
meaning of the ambiguous word
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Van Petten & Kutas (1987)
Context always supported less frequent meaning
- So, should get priming for targets related to both meanings
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Naming Time Results
25
27
44
18
24
9
At 200 msec SOA, priming smaller but still reliable for contextually inappropriate target
At 700 msec SOA, reliable priming only for the contextually appropriate target
Replicates the pattern of results in Swinney’s study (statistically, at least)
Consistent with Duffy et al.’s frequency effects
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Taken as evidence of
“backward priming”
ERP Results
- ERPs can show this because
continuous measure
rather than tapping into just
one point in time
Classic
N400
priming
effect
For first 500 msec,
Inapprop patterns
with Unrelated
Only
Approp
target
primed
Then, changes to
become more like
Approp target
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Backward Priming
• Apparent multiple access at short SOA is artifactual
– A target word related to the contextually inappropriate
meaning of an ambiguous prime word that is presented
while the prime is still being processed causes retrieval of
that inappropriate meaning
– Maybe that’s why multiple access only at short SOAs
• Rather than because context selects appropriate meaning
quickly after multiple access
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Another Possibility
In many sentences, other words in context could prime the Appropriate target
before the ambiguous prime word has any effect at all
- So early part of waveform could be due to priming from other words
- Then when the ambiguous word is processed sufficiently, it kicks in & primes both targets
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