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"Sentiment": models, code, and papers

Balancing out Bias: Achieving Fairness Through Training Reweighting

Sep 16, 2021
Xudong Han, Timothy Baldwin, Trevor Cohn

Bias in natural language processing arises primarily from models learning characteristics of the author such as gender and race when modelling tasks such as sentiment and syntactic parsing. This problem manifests as disparities in error rates across author demographics, typically disadvantaging minority groups. Existing methods for mitigating and measuring bias do not directly account for correlations between author demographics and linguistic variables. Moreover, evaluation of bias has been inconsistent in previous work, in terms of dataset balance and evaluation methods. This paper introduces a very simple but highly effective method for countering bias using instance reweighting, based on the frequency of both task labels and author demographics. We extend the method in the form of a gated model which incorporates the author demographic as an input, and show that while it is highly vulnerable to input data bias, it provides debiased predictions through demographic input perturbation, and outperforms all other bias mitigation techniques when combined with instance reweighting.

* 7 pages 

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Predicting the 2020 US Presidential Election with Twitter

Jul 19, 2021
Michael Caballero

One major sub-domain in the subject of polling public opinion with social media data is electoral prediction. Electoral prediction utilizing social media data potentially would significantly affect campaign strategies, complementing traditional polling methods and providing cheaper polling in real-time. First, this paper explores past successful methods from research for analysis and prediction of the 2020 US Presidential Election using Twitter data. Then, this research proposes a new method for electoral prediction which combines sentiment, from NLP on the text of tweets, and structural data with aggregate polling, a time series analysis, and a special focus on Twitter users critical to the election. Though this method performed worse than its baseline of polling predictions, it is inconclusive whether this is an accurate method for predicting elections due to scarcity of data. More research and more data are needed to accurately measure this method's overall effectiveness.

* 2nd International Conference on Soft Computing, Artificial Intelligence and Machine Learning, 2021, pp. 53-65 

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Intersectional Bias in Causal Language Models

Jul 16, 2021
Liam Magee, Lida Ghahremanlou, Karen Soldatic, Shanthi Robertson

To examine whether intersectional bias can be observed in language generation, we examine \emph{GPT-2} and \emph{GPT-NEO} models, ranging in size from 124 million to ~2.7 billion parameters. We conduct an experiment combining up to three social categories - gender, religion and disability - into unconditional or zero-shot prompts used to generate sentences that are then analysed for sentiment. Our results confirm earlier tests conducted with auto-regressive causal models, including the \emph{GPT} family of models. We also illustrate why bias may be resistant to techniques that target single categories (e.g. gender, religion and race), as it can also manifest, in often subtle ways, in texts prompted by concatenated social categories. To address these difficulties, we suggest technical and community-based approaches need to combine to acknowledge and address complex and intersectional language model bias.

* 18 pages, 4 figures 

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Investigating Monolingual and Multilingual BERTModels for Vietnamese Aspect Category Detection

Mar 17, 2021
Dang Van Thin, Lac Si Le, Vu Xuan Hoang, Ngan Luu-Thuy Nguyen

Aspect category detection (ACD) is one of the challenging tasks in the Aspect-based sentiment Analysis problem. The purpose of this task is to identify the aspect categories mentioned in user-generated reviews from a set of pre-defined categories. In this paper, we investigate the performance of various monolingual pre-trained language models compared with multilingual models on the Vietnamese aspect category detection problem. We conduct the experiments on two benchmark datasets for the restaurant and hotel domain. The experimental results demonstrated the effectiveness of the monolingual PhoBERT model than others on two datasets. We also evaluate the performance of the multilingual model based on the combination of whole SemEval-2016 datasets in other languages with the Vietnamese dataset. To the best of our knowledge, our research study is the first attempt at performing various available pre-trained language models on aspect category detection task and utilize the datasets from other languages based on multilingual models.

* 6 pages, 1 figure 

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Undivided Attention: Are Intermediate Layers Necessary for BERT?

Dec 22, 2020
Sharath Nittur Sridhar, Anthony Sarah

In recent times, BERT-based models have been extremely successful in solving a variety of natural language processing (NLP) tasks such as reading comprehension, natural language inference, sentiment analysis, etc. All BERT-based architectures have a self-attention block followed by a block of intermediate layers as the basic building component. However, a strong justification for the inclusion of these intermediate layers remains missing in the literature. In this work we investigate the importance of intermediate layers on the overall network performance of downstream tasks. We show that reducing the number of intermediate layers and modifying the architecture for BERT-Base results in minimal loss in fine-tuning accuracy for downstream tasks while decreasing the number of parameters and training time of the model. Additionally, we use the central kernel alignment (CKA) similarity metric and probing classifiers to demonstrate that removing intermediate layers has little impact on the learned self-attention representations.


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Domain Adversarial Fine-Tuning as an Effective Regularizer

Sep 28, 2020
Giorgos Vernikos, Katerina Margatina, Alexandra Chronopoulou, Ion Androutsopoulos

In Natural Language Processing (NLP), pre-trained language models (LMs) that are transferred to downstream tasks have been recently shown to achieve state-of-the-art results. In this work, we extend the standard fine-tuning process of pretrained LMs by introducing a new regularization technique, AFTER; domain Adversarial Fine-Tuning as an Effective Regularizer. Specifically, we complement the task-specific loss used during fine-tuning with an adversarial objective. This additional loss term is related to an adversarial classifier, that aims to discriminate between in-domain and out-of-domain text representations. In-domain refers to the labeled dataset of the task at hand while out-of-domain refers to unlabeled data from a different domain. Intuitively, the adversarial classifier acts as a regularizer which prevents the model from overfitting to the task-specific domain. Empirical results on sentiment analysis, linguistic acceptability, and paraphrase detection show that AFTERleads to improved performance compared to standard fine-tuning.

* EMNLP 2020, Findings of EMNLP 

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TextDecepter: Hard Label Black Box Attack on Text Classifiers

Aug 16, 2020
Sachin Saxena

Machine learning has been proven to be susceptible to carefully crafted samples, known as adversarialexamples. The generation of these adversarial examples helps to make the models more robust and give as an insight of the underlying decision making of these models. Over the years, researchers have successfully attacked image classifiers in, both, white and black-box setting. Although, these methods are not directly applicable to texts as text data is discrete in nature. In recent years, research on crafting adversarial examples against textual applications has been on the rise. In this paper, we present a novel approach for hard label black-box attacks against Natural Language Processing (NLP) classifiers, where no model information is disclosed, and an attacker can only query the model to get final decision of the classifier, without confidence scores of the classes involved. Such attack scenario is applicable to real world black-box models being used for security-sensitive applications such as sentiment analysis and toxic content detection

* 8 pages, 11 tables 

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Generating Diverse Story Continuations with Controllable Semantics

Sep 30, 2019
Lifu Tu, Xiaoan Ding, Dong Yu, Kevin Gimpel

We propose a simple and effective modeling framework for controlled generation of multiple, diverse outputs. We focus on the setting of generating the next sentence of a story given its context. As controllable dimensions, we consider several sentence attributes, including sentiment, length, predicates, frames, and automatically-induced clusters. Our empirical results demonstrate: (1) our framework is accurate in terms of generating outputs that match the target control values; (2) our model yields increased maximum metric scores compared to standard n-best list generation via beam search; (3) controlling generation with semantic frames leads to a stronger combination of diversity and quality than other control variables as measured by automatic metrics. We also conduct a human evaluation to assess the utility of providing multiple suggestions for creative writing, demonstrating promising results for the potential of controllable, diverse generation in a collaborative writing system.

* EMNLP 2019 Workshop on Neural Generation and Translation (WNGT2019), and non-archival acceptance in NeuralGen 2019 

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Language Model Pre-training for Hierarchical Document Representations

Jan 26, 2019
Ming-Wei Chang, Kristina Toutanova, Kenton Lee, Jacob Devlin

Hierarchical neural architectures are often used to capture long-distance dependencies and have been applied to many document-level tasks such as summarization, document segmentation, and sentiment analysis. However, effective usage of such a large context can be difficult to learn, especially in the case where there is limited labeled data available. Building on the recent success of language model pretraining methods for learning flat representations of text, we propose algorithms for pre-training hierarchical document representations from unlabeled data. Unlike prior work, which has focused on pre-training contextual token representations or context-independent {sentence/paragraph} representations, our hierarchical document representations include fixed-length sentence/paragraph representations which integrate contextual information from the entire documents. Experiments on document segmentation, document-level question answering, and extractive document summarization demonstrate the effectiveness of the proposed pre-training algorithms.


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Unsupervised Aspect Term Extraction with B-LSTM & CRF using Automatically Labelled Datasets

Sep 15, 2017
Athanasios Giannakopoulos, Claudiu Musat, Andreea Hossmann, Michael Baeriswyl

Aspect Term Extraction (ATE) identifies opinionated aspect terms in texts and is one of the tasks in the SemEval Aspect Based Sentiment Analysis (ABSA) contest. The small amount of available datasets for supervised ATE and the costly human annotation for aspect term labelling give rise to the need for unsupervised ATE. In this paper, we introduce an architecture that achieves top-ranking performance for supervised ATE. Moreover, it can be used efficiently as feature extractor and classifier for unsupervised ATE. Our second contribution is a method to automatically construct datasets for ATE. We train a classifier on our automatically labelled datasets and evaluate it on the human annotated SemEval ABSA test sets. Compared to a strong rule-based baseline, we obtain a dramatically higher F-score and attain precision values above 80%. Our unsupervised method beats the supervised ABSA baseline from SemEval, while preserving high precision scores.

* 9 pages, 3 figures, 2 tables 8th Workshop on Computational Approaches to Subjectivity, Sentiment & Social Media Analysis (WASSA), EMNLP 2017 

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