Thailand

We investigate if, given a simple symbol masking strategy,
self-attention models are capable of learning nested structures and
generalise over their depth. We do so in the simplest setting
possible, namely languages consisting of nested parentheses of several
kinds. We use encoder-only models, which we train to predict randomly
masked symbols, in a BERT-like fashion. We find that the accuracy is
well above random baseline, with accuracy consistently above 50% both
when increasing nesting depth and distances between training and
testing. However, we find that the predictions made correspond to a
simple parenthesis counting strategy, rather than a push-down
automaton. This suggests that self-attention models are not suitable
for tasks which require generalisation to more complex instances of
recursive structures than those found in the training set.

IJCNLP-AACL 2021

Can the Transformer Learn Nested Recursion with Symbol Masking?

nested structures

black box

transformer

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The great event is jointly organized by the Association for Computational Linguistics (ACL) and Asian Federation of Natural Language Processing (AFNLP).

technical paper

Stereotypical language expresses widely-held beliefs about different social categories. Many stereotypes are overtly negative, while others may appear positive on the surface, but still lead to negative consequences. In this work, we present a computational approach to interpreting stereotypes in text through the Stereotype Content Model (SCM), a comprehensive causal theory from social psychology. The SCM proposes that stereotypes can be understood along two primary dimensions: warmth and competence. We present a method for defining warmth and competence axes in semantic embedding space, and show that the four quadrants defined by this subspace accurately represent the warmth and competence concepts, according to annotated lexicons. We then apply our computational SCM model to textual stereotype data and show that it compares favourably with survey-based studies in the psychological literature. Furthermore, we explore various strategies to counter stereotypical beliefs with anti-stereotypes. It is known that countering stereotypes with anti-stereotypical examples is one of the most effective ways to reduce biased thinking, yet the problem of generating anti-stereotypes has not been previously studied. Thus, a better understanding of how to generate realistic and effective anti-stereotypes can contribute to addressing pressing societal concerns of stereotyping, prejudice, and discrimination.

Understanding and Countering Stereotypes: A Computational Approach to the Stereotype Content Model

Misinformation has recently become a well-documented matter of public concern. Existing studies on this topic have hitherto adopted a coarse concept of misinformation, which incorporates a broad spectrum of story types ranging from political conspiracies to misinterpreted pranks. This paper aims to structurize these misinformation stories by leveraging fact-check articles. Our intuition is that key phrases in a fact-check article that identify the misinformation type(s) (e.g., doctored images, urban legends) also act as rationales that determine the verdict of the fact-check (e.g., false). We experiment on rationalized models with domain knowledge as weak supervision to extract these phrases as rationales, and then cluster semantically similar rationales to summarize prevalent misinformation types. Using archived fact-checks from Snopes.com, we identify ten types of misinformation stories. We discuss how these types have evolved over the last ten years and compare their prevalence between the 2016/2020 US presidential elections and the H1N1/COVID-19 pandemics.

Structurizing Misinformation Stories via Rationalizing Fact-Checks

People debate on a variety of topics on online platforms such as Reddit, or Facebook. Debates can be lengthy, with users exchanging a wealth of information and opinions. However, conversations do not always go smoothly, and users sometimes engage in unsound argumentation techniques to prove a claim. These techniques are called fallacies. Fallacies are persuasive arguments that provide insufficient or incorrect evidence to support the claim. In this paper, we study the most frequent fallacies on Reddit, and we present them using the pragma-dialectical theory of argumentation. We construct a new annotated dataset of fallacies, using user comments containing fallacy mentions as noisy labels, and cleaning the data via crowdsourcing. Finally, we study the task of classifying fallacies using neural models. We find that generally the models perform better in the presence of conversational context.We have released the data and the code at github.com/sahaisaumya/informal_fallacies.

Breaking Down the Invisible Wall of Informal Fallacies in Online Discussions

Inferring social relations from dialogues is vital for building emotionally intelligent robots to interpret human language better and act accordingly. We model the social network as an And-or Graph, named SocAoG, for the consistency of relations among a group and leveraging attributes as inference cues. Moreover, we formulate a sequential structure prediction task, and propose an $\alpha$-$\beta$-$\gamma$ strategy to incrementally parse SocAoG for the dynamic inference upon any incoming utterance: (i) an $\alpha$ process predicting attributes and relations conditioned on the semantics of dialogues, (ii) a $\beta$ process updating the social relations based on related attributes, and (iii) a $\gamma$ process updating individual's attributes based on interpersonal social relations. Empirical results on DialogRE and MovieGraph show that our model infers social relations more accurately than the state-of-the-art methods. Moreover, the ablation study shows the three processes complement each other, and the case study demonstrates the dynamic relational inference.

SocAoG: Incremental Graph Parsing for Social Relation Inference in Dialogues

BERT has been used for solving commonsense tasks such as CommonsenseQA. While prior research has found that BERT does contain commonsense information to some extent, there has been work showing that pre-trained models can rely on spurious associations (e.g., data bias) rather than key cues in solving sentiment classification and other problems. We quantitatively investigate the presence of structural commonsense cues in BERT when solving commonsense tasks, and the importance of such cues for the model prediction. Using two different measures, we find that BERT does use relevant knowledge for solving the task, and the presence of commonsense knowledge is positively correlated to the model accuracy.

On Commonsense Cues in BERT for Solving Commonsense Tasks

In multi-hop QA, answering complex questions entails iterative document retrieval for finding the missing entity of the question. The main steps of this process are sub-question detection, document retrieval for the sub-question, and generation of a new query for the final document retrieval. However, building a dataset that contains complex questions with sub-questions and their corresponding documents requires costly human annotation. To address the issue, we propose a new method for weakly supervised multi-hop retriever pre-training without human efforts. Our method includes 1) a pre-training task for generating vector representations of complex questions, 2) a scalable data generation method that produces the nested structure of question and sub-question as weak supervision for pre-training, and 3) a pre-training model structure based on dense encoders. We conduct experiments to compare the performance of our pre-trained retriever with several state-of-the-art models on end-to-end multi-hop QA as well as document retrieval. The experimental results show that our pre-trained retriever is effective and also robust on limited data and computational resources.

Weakly Supervised Pre-Training for Multi-Hop Retriever

Existing rumor detection strategies typically provide detection labels while ignoring their explanation. Nonetheless, providing pieces of evidence to explain why a suspicious tweet is rumor is essential. As such, a novel model, LOSIRD, was proposed in this paper. First, LOSIRD mines appropriate evidence sentences and classifies them by automatically checking the veracity of the relationship of the given claim and its evidence from about 5 million Wikipedia documents. LOSIRD then automatically constructs two heterogeneous graph objects to simulate the propagation layout of the tweets and code the relationship of evidence. Finally, a graphSAGE processing component is used in LOSIRD to provide the label and evidence. To the best of our knowledge, we are the first one who combines objective facts and subjective views to verify rumor. The experimental results on two real-world Twitter datasets showed that our model exhibited the best performance in the early rumor detection task and its rumor detection performance outperformed other baseline and state-of-the-art models. Moreover, we confirmed that both objective information and subjective information are fundamental clues for rumor detection.

Meet The Truth: Leverage Objective Facts and Subjective Views for Interpretable Rumor Detection

Chinese Spell Checking (CSC) aims to detect and correct erroneous characters for user-generated text in the Chinese language. 
Most of the Chinese spelling errors are misused semantically, phonetically or graphically similar characters. 
Previous attempts noticed this phenomenon and try to use the similarity for this task. However, these methods use either heuristics or handcrafted confusion sets to predict the correct character. In this paper, we propose a Chinese spell checker called ReaLiSe, by directly leveraging the multimodal information of the Chinese characters. 
The ReaLiSe model tackles the CSC task by (1) capturing the semantic, phonetic and graphic information of the input characters, and (2) selectively mixing the information in these modalities to predict the correct output. Experiments on the SIGHAN benchmarks show that the proposed model outperforms strong baselines by a large margin.

Read, Listen, and See: Leveraging Multimodal Information Helps Chinese Spell Checking

In this paper, we propose a novel self-supervised opinion summarization framework TransSum, which models opinion summaries as translations operating on the low-dimensional aspect and sentiment embedding spaces. Specifically, we propose two contrastive objectives to learn the crucial aspect and sentiment embeddings of reviews, by taking advantage of the intra- and inter-group invariances that have not been considered in previous studies.
Furthermore, these embeddings can be used to reduce opinion redundancy and construct highly relevant reviews-summary pairs to train a supervised multi-input opinion summarization model.
Experimental results on three different domains show that TransSum outperforms several strong baselines in generating informative, relevant and low-redundant summaries, unveiling the effectiveness of our approach.

TransSum: Translating Aspect and Sentiment Embeddings for Self-Supervised Opinion Summarization

Image-text matching has been a popular research topic which bridges vision and language through semantic understanding. Recent works mainly focus on exploring the interactions between images and sentences to improve the performance without considering inference efficiency. Specifically, for the large scale databases, it is unacceptable to perform such time-consuming mechanisms between a query (text/image) and each candidate datapoint (image/text) in the whole retrieval set during inference. To tackle this problem, we propose a novel hashing based efficient inference module called HEI, which can be plugged into the existing framework to speed up the inference step without reducing the retrieval performance. In details, HEI learns to map the original datapoints into short binary hash codes and coarsely preserve the heterologous matching relationship. Thus, in the inference phase, the proposed HEI module uses the hash codes to quickly select a few candidate datapoints from the retrieval set for a given query. Then, the image-text matching model fine ranks the candidate set to find the matching datapoint. Extensive experiments on two widely used benchmark MS-COCO and Flickr30k with four baseline methods demonstrate the efficiency and effectiveness of our proposed HEI module.

Can the Transformer Learn Nested Recursion with Symbol Masking?

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Can the Transformer Learn Nested Recursion with Symbol Masking?

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Next from IJCNLP-AACL 2021

Understanding and Countering Stereotypes: A Computational Approach to the Stereotype Content Model

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AdaST: Dynamically Adapting Encoder States in the Decoder for End-to-End Speech-to-Text Translation

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