Learning Pronoun Case from Distributional Cues: Flexible Frames for Case Acquisition (2020)

Abstract: Case is an abstract grammatical feature that indicates argument relationship in a sentence. In English, cases are expressed on pronouns, as nominative case (e.g. I, he), accusative case (e.g. me, him) and genitive case (e.g. my, his). Children correctly use cased pronouns at a very young age. How do they acquire abstract case in the first place, when different cases are not associated with different meanings? This paper proposes that the distributional patterns in parents’ input could be used to distinguish grammatical cases in English.

## introduction case is a special grammatical property of nouns, pronouns, adjectives, participles or numerals whose value reflects the grammatical function performed by that word in a phrase, clause or sentence. in some languages, all of the word categories mentioned above take different inflected forms depending on their case. english, however, has largely lost its inflected cases and only expresses three cases on personal pronouns: nominative case (e.g. i, he, she), accusative case (e.g. me, him) and genitive case (e.g. my, his, her). these cases are used to mark different relationships between arguments and are commonly referred to as abstract case. for example, nominative pronouns are used as the subject of the sentence; accusative pronouns are used as the objects; and genitive pronouns are used as determiners. case is formally assigned by the +fi-nite feature in the syntactic projection. english-speaking children are able to use cased pronouns correctly at a very early age. however, between ages 2-4, they reportedly make pronoun case errors such as 'where does him go' foot_0 , 'all of they going go in here' 2 and 'what my doing' 3 . these errors might provide insights into how children acquire grammatical case. for over 40 years, researchers have proposed different explanations of abstract case acquisition based on such errors (e.g. @xcite @xcite . the syntactic explanation argues that children's knowledge of grammatical case is the result of syntactic maturation of the tense and agreement system @xcite @xcite . the morphosyntactic theory proposes that children form a paradigm for each pronoun, including features like case, person, gender and number and retrieve different forms for different contexts @xcite . in addition, parents' input has been implicated to play an important role in case acquisition. previous studies have argued that some of the children's pronoun case errors could be explained by the ambiguous uses of pronouns in parents' input. for example, pelham (2011) argued that englishspeaking children made more pronoun case errors than german-speaking children because there are more case-ambiguous pronouns (e.g. you and it) in english. @xcite suggested that children could be confused by phrases such as 'let me do it', thus producing errors like 'me do it'. are children able to learn pronoun case in the face of ambiguity? we investigated whether parents' input is informative enough for children to learn pronominal case. in english, nominative, accusative, and genitive case have different distributional patterns. for example, nominative pronouns are more likely to occur before a verb (e.g. 'i see'), whereas accusative or genitive pronouns rarely appear before a verb (e.g. '*me/my see'). however, cases do not have exclusive distributional patterns. some patterns are shared by more than one case: an accusative pronoun case precede a verb in phrases like 'let him go' or 'help me see.' @xcite . therefore, we asked if patterns of word co-occurrence could be used to differentiate pronoun cases. in the section 2, we review prior approaches using co-occurrence patterns for word categorization. in section 3, we introduce our methods and models. in section 4, we explain the setup and results of three analyses. section 5 summarizes our contributions. ## related work distributional information can be effective in grammatical categorization tasks. @xcite demonstrated that the context of a target word, including the previous words and following words, can be used to cluster the target word into different grammatical categories. their model achieved high accuracy in categorization in general; however, for words that appear in less frequent contexts, accuracy suffered. @xcite proposed that frequent local trigram frames consisting of one word before the target word and one word following it (an axb frame, where x is the target word) contain enough information for grammatical categorization. for example, in the frame 'to x to', x is likely to be a verb, e.g. 'to go to'. mintz examined the 45 most frequent axb frames in parents' input and showed that the accuracy for x's grammatical categorization was over 0.90. however, only a small portion of words appear in the frequent axb frames. in order to categorize more words, @xcite separated the axb frame into two bigram frames: ax + xb. they suggested that instead of learning the co-occurring frame 'a b' as a whole unit, it is more efficient to treat it as two flexible bigrams 'a ' and ' b' which are more useful in learning. they trained feedforward neural networks on 100,000 samples of the axb frame and the ax + xb frame had better categorization accuracy (0.73) than the axb frame (0.53). grammatical cases are similar to grammatical categories in that both reflect certain syntactic features of the word. in this paper, we trained models to predict the pronoun case of x using axb and ax + xb frames. the purpose of the study is not to provide a model to explain children's grammatical case acquisition, but to examine if the distributional patterns in parents' input are informative enough to distinguish pronoun cases. the results do not indicate whether children acquire pronoun case from parents' input but suggest a possible source from which children could learn pronoun case.