Dec 11, 2006 1

Human Parsing

Do people use probabilities for parsing?!

Sentence processing Study of Human Parsing

Dec 11, 2006 2

Sentence Processing

Issues in Sentence Processing: Word ambiguity

The pitcher (ball player/container) threw the ball (sphere/dance)

Syntactic ambiguity The bus driver hit the fireman. The bus driver was hit by the fireman.

Ambiguous thematic roles The teacher ate the spaghetti with the bus driver. The teacher ate the spaghetti with the red sauce.

Appropriate interpretation of a sentence usually requires semantic and contextual information.

Dec 11, 2006 3

Approaches

Approaches to Sentence Processing

Simple Parsing Heuristics Two-stage serial - “Garden Path”

Initial parsing and Filtering (confirming or disconfirming the structurally-determined parse)

Constraint-based or expectation-drivenProbabilistic and context-sensitive aspects of sentence processing

Dec 11, 2006 4

Theories

Ford et al (1982) Lexical sub-categorization preferenceThe woman kept the dogs on the beach

The woman kept the dogs which were on the beach 5%

The woman kept them (the dogs) on the beach 95%

“On the beach” refer to noun phrase or verb phrase

Keep has categorization preference for VP with 3 constituents

Discuss has categorization preference for VP with 2 constituents

Dec 11, 2006 5

Theories

Bever (1970) Garden Path

Temporarily ambiguous sentences One parse tree is more preferable than the

other The dispreferred parse is the correct one

Dec 11, 2006 6

Theories

Bever (1970) Garden Path

Dec 11, 2006 7

Theories

Trueswell (1993)

Subcategorization preference: Forget prefers

direct object rather than sentential complement

Dec 11, 2006 8

Theories

Trueswell (1993) Garden Path Can be measured by increased time of

reading One word or phrase at a time Eye tracking

Subjects spend more time on was for verb forget Not for a verb than prefers sentential

complement: hope

Dec 11, 2006 9

Theories

Other types of preferences Jurafsky (1996) Part of speech

The complex houses married and single students and their families

Houses more likely to be noun than verb MacDonald (1993) Verb to be head or

non head of a constituent Mitchell et al. (1995) Combination of

lexical and phrase structure frequency

Dec 11, 2006 10

Theories

Factors affecting Human Parsing Resource constraints (memory,…) Thematic structure (verb expecting

semantic agent or patient) Semantic and contextual constraints

Dec 11, 2006 11

Theories

Time Course of knowledge use?!Modularist Fraizer and Clifton (1996) Initial interpretation uses only

syntactic knowledge Semantic, Thematic and Discourse

knowledge come later

Dec 11, 2006 12

Theories

Time Course of knowledge use?!Interactionist MacDonald (1994)

Trueswell and Tanenhaus (1994) Tabor et al. (1997)

Multiple knowledge sources interactively constrain the process of interpretation

MacDonald (1994) These constraints are fundamentally probabilistic

Dec 11, 2006 13

Theories

Jurafsky (1996) and Narayanan (1996) A probabilistic model: PCFG probabilities Syntactic and thematic

subcategorization probabilities

Could account for Garden-path examples!