Clippers 11/26: Cory Shain on dissociating syntactic and semantic processing / Evan Jaffe on coreference and incremental surprisal

Title: Status report: Dissociating syntactic and semantic processing with disentangled deep contextualized representations
Presenter: Cory Shain
Abstract: Psycholinguists and cognitive scientists have long hypothesized that building syntactic structures on the one hand and building meaning representations on the other may be supported by functionally distinct components of the human sentence processing system. This idea is typically studied in controlled settings, using stimuli designed to independently manipulate syntactic and semantic processing demands (e.g. using “syntactic” vs. “semantic” violations), a paradigm which suffers from poor ecological validity and an inability to quantify the degree to which an experimental manipulation truly disentangles syntax and semantics. In this study, we follow recent work in natural language processing in attempting to learn deep contextualized word representations that automatically disentangle syntactic and semantic dimensions, using multi-task adversarial learning to encourage/discourage syntactic or semantic content in each part of the representation space. In contrast to prior work in this domain, our system produces strictly incremental word-level representations in addition to utterance-level representations, enabling us to use it to study online incremental processing patterns. Early pilot results suggest that our model effectively disentangles syntax and semantics, paving the way for using its contextualized encodings to study behavioral and neural measures of human sentence processing in more naturalistic settings.

Title: Status report: Coreference Resolution Improves Incremental Surprisal Estimation
Presenter: Evan Jaffe
Abstract: Coreference is an attractive phenomenon to examine for memory-based processing effects, given its definition of linking current and past material in discourse to form useful representations of meaning. Memory decay is a neat explanation for distance-based processing effects, and there are results showing individuals with amnesia or Alzheimer’s have degraded usage of pronouns and referring expressions. However, prediction-based effects are also a popular topic in sentence processing, resulting in numerous studies using incremental surprisal to model human behavior. Previous work (Jaffe et al 2018) found a potential memory effect for a coreference-based predictor called MentionCount when regressed to human reading time data, but did not control for the possibility of coreference driving prediction effects. Two experiments are presented that show 1) the value of adding coreference resolution to an existing parser-based incremental surprisal estimate, and 2) still show a significant effect of MentionCount even when baseline surprisal includes coreference.

Clippers 11/19: Byung-Doh Oh on Incremental Sentence Processing

Modeling incremental sentence processing with relational graph convolutional networks

We present an incremental sentence processing model in which syntactic and semantic information influence each other in an interactive manner. To this end, a PCFG-based left-corner parser (van Schijndel et al. 2013) has previously been extended to incorporate the semantic dependency predicate context (i.e. pair; Levy & Goldberg, 2014) associated with each node in the tree. In order to further improve the performance and generalizability of this model, dense representations of semantic predicate contexts and syntactic categories are learned and utilized as features for making left-corner parsing decisions. More specifically, a relational graph convolutional network (RGCN; Schlichtkrull et al. 2018) is trained to learn representations for predicates, as well as role functions for cuing the representation associated with each of its arguments. In addition, syntactic category embeddings are learned together with the left-corner parsing sub-models to minimize cross-entropy loss. Ultimately, the goal of the model is to provide a measure of predictability that is sensitive to semantic context, which in turn will serve as a baseline for testing claims about the nature of human sentence processing.

Clippers 11/12: Mounica Maddela on Hashtag Segmentation

Multi-task Pairwise Neural Ranking for Hashtag Segmentation

Mounica Maddela

Hashtags are often employed on social media with the goal of increasing discoverability, aiding search, or providing additional semantics. However, the semantic content of hashtags is not straightforward to infer as these represent ad-hoc conventions which frequently include multiple words joined together and can include abbreviations and unorthodox spellings. We build a dataset of 12,594 hashtags split into individual segments and propose a set of approaches for hashtag segmentation by framing it as a pairwise ranking problem between candidate segmentations. Our novel neural approaches demonstrate a 24.6% error reduction in hashtag segmentation accuracy compared to the current state-of-the-art method. Finally, we demonstrate that a deeper understanding of hashtag semantics obtained through segmentation is useful for downstream applications such as sentiment analysis, for which we achieved a 2.6% increase in average recall on the SemEval 2017 sentiment analysis dataset.