Week 15
The End is near...

• Final review Sunday May 8 th ?
• Final paper due Tuesday, May 10 th , 11:59pm
• Final exam Tuesday, May 10 th in class
• Last Week
– Psychological model of sentence processing
– Applications
• This Week
– Wrap-Up

• What is it calculating?
• What computational components is it composed of?
• What is it used to predict?
What phenomena does it explain?

• Situation
– You’re in a conversation.
Do you wait for sentence boundaries to interpret the meaning of a sentence?
• No!
– After only the first half of a sentence...
• meaning of words can be ambiguous
• but you still have an expectation
• Model
– Probability of each interpretation given words seen
– Stochastic CFGs, Lexical valence probabilities, N-Grams

• Syntactic Category:
– S-bias verbs (e.g. suspect) / NP-bias verbs (e.g.
remember)
– Transitive (e.g. walk the dog)/ Intransitive (e.g. walk to school)
– Participle-bias (VBD; perfect tense) (e.g. selected)/
Preterite-bias (VBN; simple past tense) (e.g.
searched)
• Semantic Fit (Thematic Fit):
– cop, witness: good agents
– crook, evidence: good patients

• “that” as a COMP (complementizer):
– [OK] The lawyer insisted that experienced diplomats would be very helpful
– That experienced diplomats would be very helpful made the lawyer confident.
• “that” a DET (determiner):
– The lawyer insisted that experienced diplomat would be very helpful
– [OK] That experienced diplomat would be very helpful to the lawyer.
Sentence-initial that interpreted as complementizer is infrequent
P(S → SBAR VP) = .00006
P(S → NP ...) = .996
Post-verbal that interpreted as determiner is infrequent

• P(w i
| w i-1
, w i-2
, …, w i-n
)
• probability of one word appearing given the preceeding n words
• “take advantage” (high probability)
• “take celebration” (low probability)

Main Verb
S
NP VP
Reduced Relative
S
NP VP
NP VP
D N VBD
D N VBN PP
The cop arrested the detective The cop arrested by

• Probability predicts human disambiguation
• Increase in reading time because of...
– Limited Parallelism
• Memory limitations cause correct interpretation to be pruned
• The horse raced past the barn fell
– Attention
• Demotion of interpretation in attentional focus
– Expectation
• Unexpected words

A good agent (e.g. the cop, the witness) makes the main verb reading more likely initially… as one hears the word
by, the RR reading becomes the more likely one: shift in attention → slower reading time and the reduced relative reading less likely lexical valence probability
(semantic fit) predicts slower reading time The witness examined by the lawyer

A good patient (e.g. the crook, the evidence) makes the RR reading more likely initially… as one hears the word
by, the ranking of the two readings do not change → no effect on reading time and the MV reading less likely lexical valence probability
(semantic fit) agrees with the RR reading The evidence examined by the lawyer

Direct Object/Sentential Complement Ambiguity. Delay from Expectation .
The athlete realized her (exercises | potential) one day might make her a world...