Capturing linguistic interaction in a grammar A method for empirically evaluating the grammar of a parsed corpus Sean Wallis Survey of English Usage University College London

Capturing linguistic interaction... Parsed corpus linguistics Empirical evaluation of grammar Experiments –Attributive AJPs –Preverbal AVPs –Embedded postmodifying clauses Conclusions –Comparing grammars or corpora –Potential applications

Parsed corpus linguistics Several million-word parsed corpora exist Each sentence analysed in the form of a tree –different languages have been analysed –limited amount of spontaneous speech data Commitment to a particular grammar required –different schemes have been applied –problems: computational completeness + manual consistency Tools support linguistic research in corpora

Parsed corpus linguistics An example tree from ICE-GB (spoken) S1A-006 #23

Parsed corpus linguistics Three kinds of evidence may be obtained from a parsed corpus  Frequency evidence of a particular known rule, structure or linguistic event  Coverage evidence of new rules, etc.  Interaction evidence of the relationship between rules, structures and events This evidence is necessarily framed within a particular grammatical scheme –So… how might we evaluate this grammar?

Empirical evaluation of grammar Many theories, frameworks and grammars –no agreed evaluation method exists –linguistics is divided into competing camps –status of parsed corpora ‘suspect’ Possible method: retrievability of events  circularity: you get out what you put in  redundancy: ‘improvement’ by mere addition  atomic: based on single events, not pattern  specificity: based on particular phenomena New method: retrievability of event sequences

Experiment 1: attributive AJPs Adjectives before a noun in English Simple idea: plot the frequency of NPs with at least n = 0, 1, 2, 3… attributive AJPs

Experiment 1: attributive AJPs Adjectives before a noun in English Simple idea: plot the frequency of NPs with at least n = 0, 1, 2, 3… attributive AJPs Raw frequencyLog frequency NB: not a straight line

Experiment 1: analysis of results If the log-frequency line is straight –exponential fall in frequency (constant probability) –no interaction between decisions (cf. coin tossing) Sequential probability analysis –calculate probability of adding each AJP –error bars (binomial) –probability falls second < first third < second fourth < second –decisions interact

Experiment 1: analysis of results If the log-frequency line is straight –exponential fall in frequency (constant probability) –no interaction between decisions (cf. coin tossing) Sequential probability analysis –calculate probability of adding each AJP –error bars (binomial) –probability falls second < first third < second fourth < second –decisions interact probability

Experiment 1: analysis of results If the log-frequency line is straight –exponential fall in frequency (constant probability) –no interaction between decisions (cf. coin tossing) Sequential probability analysis –calculate probability of adding each AJP –error bars (binomial) –probability falls –decisions interact –fit to a power law y = m.x k find m and x probability y = x

Experiment 1: explanations? Feedback loop: for each successive AJP, it is more difficult to add a further AJP –Explanation 1: semantic constraints tend to say tall green ship do not tend to say tall short ship or green tall ship –Explanation 2: communicative economy once speaker said tall green ship, tends to only say ship –Further investigation required General principle: –significant change (usually, fall) in probability is evidence of an interaction along grammatical axis

Experiments 2,3: variations  Restrict head: common and proper nouns –Common nouns: similar results –Proper nouns and adjectives are often treated as compounds (Northern England vs. lower Loire )  Ignore grammar: adjective + noun strings –Some misclassifications / miscounting (‘noise’) she was [beautiful, people] said ; tall very [green ship] –Similar results slightly weaker (third < second ns at p=0.01) –Insufficient evidence for grammar null hypothesis: simple lexical adjacency

Experiment 4: preverbal AVPs Consider adverb phrases before a verb –Results very different Probability does not fall significantly between first and second AVP Probability does fall between third and second AVP –Possible constraints (weak) communicative not (strong) semantic –Further investigation needed

Experiment 4: preverbal AVPs Consider adverb phrases before a verb –Results very different Probability does not fall significantly between first and second AVP Probability does fall between third and second AVP –Possible constraints (weak) communicative not (strong) semantic –Further investigation needed –Not power law: R 2 < 0.24 probability

Experiment 5: embedded clauses Another way to specify nouns in English –add clause after noun to explicate it the ship [that was tall and green] the ship [in the port] –may be embedded the ship [in the port [with the ancient lighthouse]] –or successively postmodified the ship [in the port][with a very old mast] Compare successive embedding and sequential postmodifying clauses –Axis = embedding depth / sequence length

Experiment 5: method Extract examples with FTFs –at least n levels of embedded postmodification:

Experiment 5: method Extract examples with FTFs –at least n levels of embedded postmodification: (etc.)

Experiment 5: method Extract examples with FTFs –at least n levels of embedded postmodification: –problems: multiple matching cases (use ICECUP IV to classify) overlapping cases (subtract extra case) co-ordination of clauses or NPs (use alternative patterns) (etc.)

Experiment 5: analysis of results Probability of adding a further embedded clause falls with each level –second < first –sequential < embedding Embedding only: –third < first –insufficient data for third < second Conclusion: –Interaction along embedding and sequential axes

Experiment 5: analysis of results Probability of adding a further embedded clause falls with each level –second < first –sequential < embedding Embedding only: –third < first –insufficient data for third < second Conclusion: –Interaction along embedding and sequential axes sequential embedded probability

Experiment 5: analysis of results Probability of adding a further embedded clause falls with each level –second < first –sequential < embedding Fitting to f = m.x k –k < 0 = fall ( f = m/x |k| ) –|k| is high = steep Conclusion: –Both match power law: R 2 > 0.99 sequential embedded y = x y = x

Experiment 5: explanations? Lexical adjacency? –No: 87% of 2-level cases have at least one VP, NP or clause between upper and lower heads Misclassified cases of embedding? –No: very few (5%) semantically ambiguous cases Language production constraints? –Possibly, could also be communicative economy contrast spontaneous speech with other modes Positive ‘proof’ of recursive tree grammar –Established from parsed corpus –cf. negative ‘proof’ (NLP parsing problems)

Conclusions A new method for evaluating interactions along grammatical axes –General purpose, robust, structural –More abstract than ‘linguistic choice’ experiments –Depends on a concept of grammatical distance along an axis, based on the chosen grammar Method has philosophical implications –Grammar viewed as structure of linguistic choices –Linguistics as an evaluable observational science Signature (trace) of language production decisions –A unification of theoretical and corpus linguistics?

Comparing grammars or corpora Can we reliably retrieve known interaction patterns with different grammars? –Do these patterns differ across corpora? Benefits over individual event retrieval non-circular: generalisation across local syntax not subject to redundancy: arbitrary terms makes trends more difficult to retrieve not atomic: based on patterns of interaction general: patterns may have multiple explanations Supplements retrieval of events

Potential applications Corpus linguistics –Optimising existing grammar e.g. co-ordination, compound nouns Theoretical linguistics –Comparing different grammars, same language –Comparing different languages or periods Psycholinguistics –Search for evidence of language production constraints in spontaneous speech corpora speech and language therapy language acquisition and development

Links and further reading Survey of English Usage – Corpora and grammar –.../projects/ice-gb Full paper –.../staff/sean/resources/analysing-grammatical- interaction.pdf Sequential analysis spreadsheet (Excel) –.../staff/sean/resources/interaction-trends.xls