個人が用いる単語の意味のモデル化とその応用

学位の種別: 修士University of Tokyo(東京大学

PerPLM: Personalized Fine-tuning of Pretrained Language Models via Writer-specific Intermediate Learning and Prompts

The meanings of words and phrases depend not only on where they are used (contexts) but also on who use them (writers). Pretrained language models (PLMs) are powerful tools for capturing context, but they are typically pretrained and fine-tuned for universal use across different writers. This study aims to improve the accuracy of text understanding tasks by personalizing the fine-tuning of PLMs for specific writers. We focus on a general setting where only the plain text from target writers are available for personalization. To avoid the cost of fine-tuning and storing multiple copies of PLMs for different users, we exhaustively explore using writer-specific prompts to personalize a unified PLM. Since the design and evaluation of these prompts is an underdeveloped area, we introduce and compare different types of prompts that are possible in our setting. To maximize the potential of prompt-based personalized fine-tuning, we propose a personalized intermediate learning based on masked language modeling to extract task-independent traits of writers' text. Our experiments, using multiple tasks, datasets, and PLMs, reveal the nature of different prompts and the effectiveness of our intermediate learning approach.Comment: 11 page

The Media Bias Taxonomy: A Systematic Literature Review on the Forms and Automated Detection of Media Bias

The way the media presents events can significantly affect public perception, which in turn can alter people's beliefs and views. Media bias describes a one-sided or polarizing perspective on a topic. This article summarizes the research on computational methods to detect media bias by systematically reviewing 3140 research papers published between 2019 and 2022. To structure our review and support a mutual understanding of bias across research domains, we introduce the Media Bias Taxonomy, which provides a coherent overview of the current state of research on media bias from different perspectives. We show that media bias detection is a highly active research field, in which transformer-based classification approaches have led to significant improvements in recent years. These improvements include higher classification accuracy and the ability to detect more fine-granular types of bias. However, we have identified a lack of interdisciplinarity in existing projects, and a need for more awareness of the various types of media bias to support methodologically thorough performance evaluations of media bias detection systems. Concluding from our analysis, we see the integration of recent machine learning advancements with reliable and diverse bias assessment strategies from other research areas as the most promising area for future research contributions in the field

A Dynamic Embedding Model of the Media Landscape

Information about world events is disseminated through a wide variety of news channels, each with specific considerations in the choice of their reporting. Although the multiplicity of these outlets should ensure a variety of viewpoints, recent reports suggest that the rising concentration of media ownership may void this assumption. This observation motivates the study of the impact of ownership on the global media landscape and its influence on the coverage the actual viewer receives. To this end, the selection of reported events has been shown to be informative about the high-level structure of the news ecosystem. However, existing methods only provide a static view into an inherently dynamic system, providing underperforming statistical models and hindering our understanding of the media landscape as a whole. In this work, we present a dynamic embedding method that learns to capture the decision process of individual news sources in their selection of reported events while also enabling the systematic detection of large-scale transformations in the media landscape over prolonged periods of time. In an experiment covering over 580M real-world event mentions, we show our approach to outperform static embedding methods in predictive terms. We demonstrate the potential of the method for news monitoring applications and investigative journalism by shedding light on important changes in programming induced by mergers and acquisitions, policy changes, or network-wide content diffusion. These findings offer evidence of strong content convergence trends inside large broadcasting groups, influencing the news ecosystem in a time of increasing media ownership concentration

Methods for detecting and mitigating linguistic bias in text corpora

Im Zuge der fortschreitenden Ausbreitung des Webs in alle Aspekte des täglichen Lebens wird Bias in Form von Voreingenommenheit und versteckten Meinungen zu einem zunehmend herausfordernden Problem. Eine weitverbreitete Erscheinungsform ist Bias in Textdaten. Um dem entgegenzuwirken hat die Online-Enzyklopädie Wikipedia das Prinzip des neutralen Standpunkts (Englisch: Neutral Point of View, kurz: NPOV) eingeführt, welcher die Verwendung neutraler Sprache und die Vermeidung von einseitigen oder subjektiven Formulierungen vorschreibt. Während Studien gezeigt haben, dass die Qualität von Wikipedia-Artikel mit der Qualität von Artikeln in klassischen Enzyklopädien vergleichbar ist, zeigt die Forschung gleichzeitig auch, dass Wikipedia anfällig für verschiedene Typen von NPOV-Verletzungen ist. Bias zu identifizieren, kann eine herausfordernde Aufgabe sein, sogar für Menschen, und mit Millionen von Artikeln und einer zurückgehenden Anzahl von Mitwirkenden wird diese Aufgabe zunehmend schwieriger. Wenn Bias nicht eingedämmt wird, kann dies nicht nur zu Polarisierungen und Konflikten zwischen Meinungsgruppen führen, sondern Nutzer auch negativ in ihrer freien Meinungsbildung beeinflussen. Hinzu kommt, dass sich Bias in Texten und in Ground-Truth-Daten negativ auf Machine Learning Modelle, die auf diesen Daten trainiert werden, auswirken kann, was zu diskriminierendem Verhalten von Modellen führen kann. In dieser Arbeit beschäftigen wir uns mit Bias, indem wir uns auf drei zentrale Aspekte konzentrieren: Bias-Inhalte in Form von geschriebenen Aussagen, Bias von Crowdworkern während des Annotierens von Daten und Bias in Word Embeddings Repräsentationen. Wir stellen zwei Ansätze für die Identifizierung von Aussagen mit Bias in Textsammlungen wie Wikipedia vor. Unser auf Features basierender Ansatz verwendet Bag-of-Word Features inklusive einer Liste von Bias-Wörtern, die wir durch das Identifizieren von Clustern von Bias-Wörtern im Vektorraum von Word Embeddings zusammengestellt haben. Unser verbesserter, neuronaler Ansatz verwendet Gated Recurrent Neural Networks, um Kontext-Abhängigkeiten zu erfassen und die Performance des Modells weiter zu verbessern. Unsere Studie zum Thema Crowd Worker Bias deckt Bias-Verhalten von Crowdworkern mit extremen Meinungen zu einem bestimmten Thema auf und zeigt, dass dieses Verhalten die entstehenden Ground-Truth-Label beeinflusst, was wiederum Einfluss auf die Erstellung von Datensätzen für Aufgaben wie Bias Identifizierung oder Sentiment Analysis hat. Wir stellen Ansätze für die Abschwächung von Worker Bias vor, die Bewusstsein unter den Workern erzeugen und das Konzept der sozialen Projektion verwenden. Schließlich beschäftigen wir uns mit dem Problem von Bias in Word Embeddings, indem wir uns auf das Beispiel von variierenden Sentiment-Scores für Namen konzentrieren. Wir zeigen, dass Bias in den Trainingsdaten von den Embeddings erfasst und an nachgelagerte Modelle weitergegeben wird. In diesem Zusammenhang stellen wir einen Debiasing-Ansatz vor, der den Bias-Effekt reduziert und sich positiv auf die produzierten Label eines nachgeschalteten Sentiment Classifiers auswirkt

Dynamic Contextualized Word Embeddings

Static word embeddings that represent words by a single vector cannot capture the variability of word meaning in different linguistic and extralinguistic contexts. Building on prior work on contextualized and dynamic word embeddings, we introduce dynamic contextualized word embeddings that represent words as a function of both linguistic and extralinguistic context. Based on a pretrained language model (PLM), dynamic contextualized word embeddings model time and social space jointly, which makes them attractive for a range of NLP tasks involving semantic variability. We highlight potential application scenarios by means of qualitative and quantitative analyses on four English datasets

The Lifecycle of "Facts": A Survey of Social Bias in Knowledge Graphs

Knowledge graphs are increasingly used in a plethora of downstream tasks or in the augmentation of statistical models to improve factuality. However, social biases are engraved in these representations and propagate downstream. We conducted a critical analysis of literature concerning biases at different steps of a knowledge graph lifecycle. We investigated factors introducing bias, as well as the biases that are rendered by knowledge graphs and their embedded versions afterward. Limitations of existing measurement and mitigation strategies are discussed and paths forward are proposed.Comment: Accepted to AACL-IJCNLP 202

Explainability in Music Recommender Systems

The most common way to listen to recorded music nowadays is via streaming platforms which provide access to tens of millions of tracks. To assist users in effectively browsing these large catalogs, the integration of Music Recommender Systems (MRSs) has become essential. Current real-world MRSs are often quite complex and optimized for recommendation accuracy. They combine several building blocks based on collaborative filtering and content-based recommendation. This complexity can hinder the ability to explain recommendations to end users, which is particularly important for recommendations perceived as unexpected or inappropriate. While pure recommendation performance often correlates with user satisfaction, explainability has a positive impact on other factors such as trust and forgiveness, which are ultimately essential to maintain user loyalty. In this article, we discuss how explainability can be addressed in the context of MRSs. We provide perspectives on how explainability could improve music recommendation algorithms and enhance user experience. First, we review common dimensions and goals of recommenders' explainability and in general of eXplainable Artificial Intelligence (XAI), and elaborate on the extent to which these apply -- or need to be adapted -- to the specific characteristics of music consumption and recommendation. Then, we show how explainability components can be integrated within a MRS and in what form explanations can be provided. Since the evaluation of explanation quality is decoupled from pure accuracy-based evaluation criteria, we also discuss requirements and strategies for evaluating explanations of music recommendations. Finally, we describe the current challenges for introducing explainability within a large-scale industrial music recommender system and provide research perspectives.Comment: To appear in AI Magazine, Special Topic on Recommender Systems 202

Reflections on the nature of measurement in language-based automated assessments of patients' mental state and cognitive function

Modern advances in computational language processing methods have enabled new approaches to the measurement of mental processes. However, the field has primarily focused on model accuracy in predicting performance on a task or a diagnostic category. Instead the field should be more focused on determining which computational analyses align best with the targeted neurocognitive/psychological functions that we want to assess. In this paper we reflect on two decades of experience with the application of language-based assessment to patients' mental state and cognitive function by addressing the questions of what we are measuring, how it should be measured and why we are measuring the phenomena. We address the questions by advocating for a principled framework for aligning computational models to the constructs being assessed and the tasks being used, as well as defining how those constructs relate to patient clinical states. We further examine the assumptions that go into the computational models and the effects that model design decisions may have on the accuracy, bias and generalizability of models for assessing clinical states. Finally, we describe how this principled approach can further the goal of transitioning language-based computational assessments to part of clinical practice while gaining the trust of critical stakeholders