Neural induction of a lexicon for fast and interpretable stance classification.

Large-scale social media classification faces the following two challenges: algorithms can be hard to adapt to Web-scale data, and the predictions that they provide are difficult for humans to understand. Those two challenges are solved at the cost of some accuracy by lexicon-based classifiers, which offer a white-box approach to text mining by using a trivially interpretable additive model. However current techniques for lexicon-based classification limit themselves to using hand-crafted lexicons, which suffer from human bias and are difficult to extend, or automatically generated lexicons, which are induced using point-estimates of some predefined probabilistic measure on a corpus of interest. In this work we propose a new approach to learn robust lexicons, using the backpropagation algorithm to ensure generalization power without sacrificing model readability. We evaluate our approach on a stance detection task, on two different datasets, and find that our lexicon outperforms standard lexicon approaches

Representation and learning schemes for argument stance mining.

Argumentation is a key part of human interaction. Used introspectively, it searches for the truth, by laying down argument for and against positions. As a mediation tool, it can be used to search for compromise between multiple human agents. For this purpose, theories of argumentation have been in development since the Ancient Greeks in order to formalise the process and therefore remove the human imprecision from it. From this practice the process of argument mining has emerged. As human interaction has moved from the small scale of one-to-one (or few-to-few) debates to large scale discussions where tens of thousands of participants can express their opinion in real time, the importance of argument mining has grown while its feasibility in a manual annotation setting has diminished and relied mainly on a human-defined heuristics to process the data. This underlines the importance of a new generation of computational tools that can automate this process on a larger scale. In this thesis we study argument stance detection, one of the steps involved in the argument mining workflow. We demonstrate how we can use data of varying reliability in order to mine argument stance in social media data. We investigate a spectrum of techniques, from completely unsupervised classification of stance using a sentiment lexicon, automated computation of a regularised stance lexicon, automated computation of a lexicon with modifiers, and the use of a lexicon with modifiers as a temporal feature model for more complex classification algorithms. We find that the addition of contextual information enhances unsupervised stance classification, within reason, and that multi-strategy algorithms that combine multiple heuristics by ordering them from the precise to the general tend to outperform other approaches by a large margin. Focusing then on building a stance lexicon, we find that optimising such lexicons using an empirical risk minimisation framework allows us to regularise them to a higher degree than competing probabilistic techniques, which helps us learn better lexicons from noisy data. We also conclude that adding local context (neighbouring words) information during the learning phase of the lexicons tends to produce more accurate results at the cost of robustness, since part of the weights is distributed from the words with a class valence to the contextual words. Finally, when investigating the use of lexicons to build feature models for traditional machine learning techniques, simple lexicons (without context) seem to perform overall as well as more complex ones, and better than purely semantic representations. We also find that word-level feature models tend to outperform sentence and instance-level representations, but that they do not benefit as much from being augmented by lexicon knowledge.This research programme was carried out in collaboration with the University of Glasgow, Department of Computer Science

Classification of Explainable Artificial Intelligence Methods through Their Output Formats

Machine and deep learning have proven their utility to generate data-driven models with high accuracy and precision. However, their non-linear, complex structures are often difficult to interpret. Consequently, many scholars have developed a plethora of methods to explain their functioning and the logic of their inferences. This systematic review aimed to organise these methods into a hierarchical classification system that builds upon and extends existing taxonomies by adding a significant dimension—the output formats. The reviewed scientific papers were retrieved by conducting an initial search on Google Scholar with the keywords “explainable artificial intelligence”; “explainable machine learning”; and “interpretable machine learning”. A subsequent iterative search was carried out by checking the bibliography of these articles. The addition of the dimension of the explanation format makes the proposed classification system a practical tool for scholars, supporting them to select the most suitable type of explanation format for the problem at hand. Given the wide variety of challenges faced by researchers, the existing XAI methods provide several solutions to meet the requirements that differ considerably between the users, problems and application fields of artificial intelligence (AI). The task of identifying the most appropriate explanation can be daunting, thus the need for a classification system that helps with the selection of methods. This work concludes by critically identifying the limitations of the formats of explanations and by providing recommendations and possible future research directions on how to build a more generally applicable XAI method. Future work should be flexible enough to meet the many requirements posed by the widespread use of AI in several fields, and the new regulation

Sentiment Lexicon Induction and Interpretable Multiple-instance Learning in Financial Markets

Sentiment analysis has been widely used in the domain of finance. There are two most common textual sentiment analysis methods in finance: \textit{dictionary-based approach} and \textit{machine learning approach}. The dictionary-based method is the most convenient and efficient method to extract sentiments from the text, but the words in the dictionary are limited and cannot capture the full scope of a particular domain. Additionally, it is expensive and unsustainable to manually create and maintain domain-specific dictionary using expert opinions. Deep learning models become mainstream methods in sentiment analysis because of their better performance by utilizing extra information on a larger corpus and more complex model structures. However, deep learning models often suffer from the interpretability problem. This thesis is an attempt to address the issues of both methods. It proposes a machine learning method to do a corpus-based sentiment lexicon induction, which extends the sentiment dictionary that is customized to analyze corporate conference calls. The new extended dictionary is shown to have a better performance than the original dictionary in terms of the three-day returns of the companies in the MSCI universe. It also proposes a highly interpretable attention-based multiple-instance learning model to perform sentiment classification. It also shows that the newly proposed model has comparable accuracy performance to the state-of-the-art sequential models with better interpretability. A keyword ranking is also generated by the model as a by-product. A new sentiment dictionary is also generated by the deep learning method and shows even better performance than both the extended dictionary and the original dictionary

An Empirical Study of Offensive Language in Online Interactions

In the past decade, usage of social media platforms has increased significantly. People use these platforms to connect with friends and family, share information, news and opinions. Platforms such as Facebook, Twitter are often used to propagate offensive and hateful content online. The open nature and anonymity of the internet fuels aggressive and inflamed conversations. The companies and federal institutions are striving to make social media cleaner, welcoming and unbiased. In this study, we first explore the underlying topics in popular offensive language datasets using statistical and neural topic modeling. The current state-of-the-art models for aggression detection only present a toxicity score based on the entire post. Content moderators often have to deal with lengthy texts without any word-level indicators. We propose a neural transformer approach for detecting the tokens that make a particular post aggressive. The pre-trained BERT model has achieved state-of-the-art results in various natural language processing tasks. However, the model is trained on general-purpose corpora and lacks aggressive social media linguistic features. We propose fBERT, a retrained BERT model with over $1.4$ million offensive tweets from the SOLID dataset. We demonstrate the effectiveness and portability of fBERT over BERT in various shared offensive language detection tasks. We further propose a new multi-task aggression detection (MAD) framework for post and token-level aggression detection using neural transformers. The experiments confirm the effectiveness of the multi-task learning model over individual models; particularly when the number of training data is limited

Artificial Neural Network methods applied to sentiment analysis

Sentiment Analysis (SA) is the study of opinions and emotions that are conveyed by text. This field of study has commercial applications for example in market research (e.g., “What do customers like and dislike about a product?”) and consumer behavior (e.g., “Which book will a customer buy next when he wrote a positive review about book X?”). A private person can benefit from SA by automatic movie or restaurant recommendations, or from applications on the computer or smart phone that adapt to the user’s current mood. In this thesis we will put forward research on artificial Neural Network (NN) methods applied to SA. Many challenges arise, such as sarcasm, domain dependency, and data scarcity, that need to be addressed by a successful system. In the first part of this thesis we perform linguistic analysis of a word (“hard”) under the light of SA. We show that sentiment-specific word sense disambiguation is necessary to distinguish fine nuances of polarity. Commonly available resources are not sufficient for this. The introduced Contextually Enhanced Sentiment Lexicon (CESL) is used to label occurrences of “hard” in a real dataset with its sense. That allows us to train a Support Vector Machine (SVM) with deep learning features that predicts the polarity of a single occurrence of the word, just given its context words. We show that the features we propose improve the result compared to existing standard features. Since the labeling effort is not negligible, we propose a clustering approach that reduces the manual effort to a minimum. The deep learning features that help predicting fine-grained, context-dependent polarity are computed by a Neural Network Language Model (NNLM), namely a variant of the Log-Bilinear Language model (LBL). By improving this model the performance of polarity classification might as well improve. Thus, we propose a non-linear version of the LBL and the vectorized Log-Bilinear Language model (vLBL), because non-linear models are generally considered more powerful. In a parameter study on a language modeling task, we show that the non-linear versions indeed perform better than their linear counterparts. However, the difference is small, except for settings where the model has only few parameters, which might be the case when little training data is available and the model therefore needs to be smaller in order to avoid overfitting. An alternative approach to fine-grained polarity classification as used above is to train classifiers that will do the distinction automatically. Due to the complexity of the task, the challenges of SA in general, and certain domain-specific issues (e.g., when using Twitter text) existing systems have much room to improve. Often statistical classifiers are used with simple Bag-of-Words (BOW) features or count features that stem from sentiment lexicons. We introduce a linguistically-informed Convolutional Neural Network (lingCNN) that builds upon the fact that there has been much research on language in general and sentiment lexicons in particular. lingCNN makes use of two types of linguistic features: word-based and sentence-based. Word-based features comprise features derived from sentiment lexicons, such as polarity or valence and general knowledge about language, such as a negation-based feature. Sentence-based features are also based on lexicon counts and valences. The combination of both types of features is superior to the original model without these features. Especially, when little training data is available (that can be the case for different languages that are underresourced), lingCNN proves to be significantly better (up to 12 macro-F1 points). Although, linguistic features in terms of sentiment lexicons are beneficial, their usage gives rise to a new set of problems. Most lexicons consist of infinitive forms of words only. Especially, lexicons for low-resource languages. However, the text that needs to be classified is unnormalized. Hence, we want to answer the question if morphological information is necessary for SA or if a system that neglects all this information and therefore can make better use of lexicons actually has an advantage. Our approach is to first stem or lemmatize a dataset and then perform polarity classification on it. On Czech and English datasets we show that better results can be achieved with normalization. As a positive side effect, we can compute better word embeddings by first normalizing the training corpus. This works especially well for languages that have rich morphology. We show on word similarity datasets for English, German, and Spanish that our embeddings improve performance. On a new WordNet-based evaluation we confirm these results on five different languages (Czech, English, German, Hungarian, and Spanish). The benefit of this new evaluation is further that it can be used for many other languages, as the only resource that is required is a WordNet. In the last part of the thesis, we use a recently introduced method to create an ultradense sentiment space out of generic word embeddings. This method allows us to compress 400 dimensional word embeddings down to 40 or even just 4 dimensions and still get similar results on a polarity classification task. While the training speed increases by a factor of 44, the difference in classification performance is not significant.Sentiment Analyse (SA) ist das Untersuchen von Meinungen und Emotionen die durch Text übermittelt werden. Dieses Forschungsgebiet findet kommerzielle Anwendungen in Marktforschung (z.B.: „Was mögen Kunden an einem Produkt (nicht)?“) und Konsumentenverhalten (z.B.: „Welches Buch wird ein Kunde als nächstes kaufen, nachdem er eine positive Rezension über Buch X geschrieben hat?“). Aber auch als Privatperson kann man von Forschung in SA profitieren. Beispiele hierfür sind automatisch erstellte Film- oder Restaurantempfehlungen oder Anwendungen auf Computer oder Smartphone die sich der aktuellen Stimmungslage des Benutzers anpassen. In dieser Arbeit werden wir Forschung auf dem Gebiet der Neuronen Netze (NN) angewendet auf SA vorantreiben. Dabei ergeben sich viele Herausforderungen, wie Sarkasmus, Domänenabhängigkeit und Datenarmut, die ein erfolgreiches System angehen muss. Im ersten Teil der Arbeit führen wir eine linguistische Analyse des englischen Wortes „hard“ in Hinblick auf SA durch. Wir zeigen, dass sentiment-spezifische Wortbedeutungsdisambiguierung notwendig ist, um feine Nuancen von Polarität (positive vs. negative Stimmung) unterscheiden zu können. Häufig verwendete, frei verfügbare Ressourcen sind dafür nicht ausreichend. Daher stellen wir CESL (Contextually Enhanced Sentiment Lexicon), ein sentiment-spezifisches Bedeutungslexicon vor, welches verwendet wird, um Vorkommen von „hard“ in einem realen Datensatz mit seinen Bedeutungen zu versehen. Das Lexikon erlaubt es eine Support Vector Machine (SVM) mit Features aus dem Deep Learning zu trainieren, die in der Lage ist, die Polarität eines Vorkommens nur anhand seiner Kontextwörter vorherzusagen. Wir zeigen, dass die vorgestellten Features die Ergebnisse der SVM verglichen mit Standard-Features verbessern. Da der Aufwand für das Erstellen von markierten Trainingsdaten nicht zu unterschätzen ist, stellen wir einen Clustering-Ansatz vor, der den manuellen Markierungsaufwand auf ein Minimum reduziert. Die Deep Learning Features, die die Vorhersage von feingranularer, kontextabhängiger Polarität verbessern, werden mittels eines neuronalen Sprachmodells, genauer eines Log-Bilinear Language model (LBL)s, berechnet. Wenn man dieses Modell verbessert, wird vermutlich auch das Ergebnis der Polaritätsklassifikation verbessert. Daher führen wir nichtlineare Versionen des LBL und vectorized Log-Bilinear Language model (vLBL) ein, weil nichtlineare Modelle generell als mächtiger angesehen werden. In einer Parameterstudie zur Sprachmodellierung zeigen wir, dass nichtlineare Modelle tatsächlich besser abschneiden, als ihre linearen Gegenstücke. Allerdings ist der Unterschied gering, es sei denn die Modelle können nur auf wenige Parameter zurückgreifen. So etwas kommt zum Beispiel vor, wenn nur wenige Trainingsdaten verfügbar sind und das Modell deshalb kleiner sein muss, um Überanpassung zu verhindern. Ein alternativer Ansatz zur feingranularen Polaritätsklassifikation wie oben verwendet, ist es, einen Klassifikator zu trainieren, der die Unterscheidung automatisch vornimmt. Durch die Komplexität der Aufgabe, der Herausforderungen von SA im Allgemeinen und speziellen domänenspezifischen Problemen (z.B.: wenn Twitter-Daten verwendet werden) haben existierende Systeme noch immer großes Optimierungspotential. Oftmals verwenden statistische Klassifikatoren einfache Bag-of-Words (BOW)-Features. Alternativ kommen Zähl-Features zum Einsatz, die auf Sentiment-Lexika aufsetzen. Wir stellen linguistically-informed Convolutional Neural Network (lingCNN) vor, dass auf dem Fakt beruht, dass bereits viel Forschung in Sprachen und Sentiment-Lexika geflossen ist. lingCNN macht von zwei linguistischen Feature-Typen Gebrauch: wortbasierte und satzbasierte. Wort-basierte Features umfassen Features die von Sentiment-Lexika, wie Polarität oder Valenz (die Stärke der Polarität) und generellem Wissen über Sprache, z.B.: Verneinung, herrühren. Satzbasierte Features basieren ebenfalls auf Zähl-Features von Lexika und auf Valenzen. Die Kombination beider Feature-Typen ist dem Originalmodell ohne linguistische Features überlegen. Besonders wenn wenige Trainingsdatensätze vorhanden sind (das kann der Fall für Sprachen sein, die weniger erforscht sind als englisch). lingCNN schneidet signifikant besser ab (bis zu 12 macro-F1 Punkte). Obwohl linguistische Features basierend auf Sentiment-Lexika vorteilhaft sind, führt deren Verwendung zu neuen Problemen. Der Großteil der Lexika enthält nur Infinitivformen der Wörter. Dies gilt insbesondere für Sprachen mit wenigen Ressourcen. Das ist eine Herausforderung, weil der Text der klassifiziert werden soll in der Regel nicht normalisiert ist. Daher wollen wir die Frage beantworten, ob morphologische Information für SA überhaupt notwendig ist oder ob ein System, dass jegliche morphologische Information ignoriert und dadurch bessere Verwendung der Lexika erzielt, einen Vorteil genießt. Unser Ansatz besteht aus Stemming und Lemmatisierung des Datensatzes, bevor dann die Polaritätsklassifikation durchgeführt wird. Auf englischen und tschechischen Daten zeigen wir, dass durch Normalisierung bessere Ergebnisse erzielt werden. Als positiven Nebeneffekt kann man bessere Wortrepresentationen (engl. word embeddings) berechnen, indem das Trainingskorpus zuerst normalisiert wird. Das funktioniert besonders gut für morphologisch reiche Sprachen. Wir zeigen auf Datensätzen zur Wortähnlichkeit für deutsch, englisch und spanisch, dass unsere Wortrepresentationen die Ergebnisse verbessern. In einer neuen WordNet-basierten Evaluation bestätigen wir diese Ergebnisse für fünf verschiedene Sprachen (deutsch, englisch, spanisch, tschechisch und ungarisch). Der Vorteil dieser Evaluation ist weiterhin, dass sie für viele Sprachen angewendet werden kann, weil sie lediglich ein WordNet als Ressource benötigt. Im letzten Teil der Arbeit verwenden wir eine kürzlich vorgestellte Methode zur Erstellen eines ultradichten Sentiment-Raumes aus generischen Wortrepresentationen. Diese Methode erlaubt es uns 400 dimensionale Wortrepresentationen auf 40 oder sogar nur 4 Dimensionen zu komprimieren und weiterhin die gleichen Resultate in Polaritätsklassifikation zu erhalten. Während die Trainingsgeschwindigkeit um einen Faktor von 44 verbessert wird, sind die Unterschiede in der Polaritätsklassifikation nicht signifikant

Natural Language Processing using Deep Learning in Social Media

[ES] En los últimos años, los modelos de aprendizaje automático profundo (AP) han revolucionado los sistemas de procesamiento de lenguaje natural (PLN). Hemos sido testigos de un avance formidable en las capacidades de estos sistemas y actualmente podemos encontrar sistemas que integran modelos PLN de manera ubicua. Algunos ejemplos de estos modelos con los que interaccionamos a diario incluyen modelos que determinan la intención de la persona que escribió un texto, el sentimiento que pretende comunicar un tweet o nuestra ideología política a partir de lo que compartimos en redes sociales. En esta tesis se han propuestos distintos modelos de PNL que abordan tareas que estudian el texto que se comparte en redes sociales. En concreto, este trabajo se centra en dos tareas fundamentalmente: el análisis de sentimientos y el reconocimiento de la personalidad de la persona autora de un texto. La tarea de analizar el sentimiento expresado en un texto es uno de los problemas principales en el PNL y consiste en determinar la polaridad que un texto pretende comunicar. Se trata por lo tanto de una tarea estudiada en profundidad de la cual disponemos de una vasta cantidad de recursos y modelos. Por el contrario, el problema del reconocimiento de personalidad es una tarea revolucionaria que tiene como objetivo determinar la personalidad de los usuarios considerando su estilo de escritura. El estudio de esta tarea es más marginal por lo que disponemos de menos recursos para abordarla pero que no obstante presenta un gran potencial. A pesar de que el enfoque principal de este trabajo fue el desarrollo de modelos de aprendizaje profundo, también hemos propuesto modelos basados en recursos lingüísticos y modelos clásicos del aprendizaje automático. Estos últimos modelos nos han permitido explorar las sutilezas de distintos elementos lingüísticos como por ejemplo el impacto que tienen las emociones en la clasificación correcta del sentimiento expresado en un texto. Posteriormente, tras estos trabajos iniciales se desarrollaron modelos AP, en particular, Redes neuronales convolucionales (RNC) que fueron aplicadas a las tareas previamente citadas. En el caso del reconocimiento de la personalidad, se han comparado modelos clásicos del aprendizaje automático con modelos de aprendizaje profundo, pudiendo establecer una comparativa bajo las mismas premisas. Cabe destacar que el PNL ha evolucionado drásticamente en los últimos años gracias al desarrollo de campañas de evaluación pública, donde múltiples equipos de investigación comparan las capacidades de los modelos que proponen en las mismas condiciones. La mayoría de los modelos presentados en esta tesis fueron o bien evaluados mediante campañas de evaluación públicas, o bien emplearon la configuración de una campaña pública previamente celebrada. Siendo conscientes, por lo tanto, de la importancia de estas campañas para el avance del PNL, desarrollamos una campaña de evaluación pública cuyo objetivo era clasificar el tema tratado en un tweet, para lo cual recogimos y etiquetamos un nuevo conjunto de datos. A medida que avanzabamos en el desarrollo del trabajo de esta tesis, decidimos estudiar en profundidad como las RNC se aplicaban a las tareas de PNL. En este sentido, se exploraron dos líneas de trabajo. En primer lugar, propusimos un método de relleno semántico para RNC, que plantea una nueva manera de representar el texto para resolver tareas de PNL. Y en segundo lugar, se introdujo un marco teórico para abordar una de las críticas más frecuentes del aprendizaje profundo, el cual es la falta de interpretabilidad. Este marco busca visualizar qué patrones léxicos, si los hay, han sido aprendidos por la red para clasificar un texto.[CA] En els últims anys, els models d'aprenentatge automàtic profund (AP) han revolucionat els sistemes de processament de llenguatge natural (PLN). Hem estat testimonis d'un avanç formidable en les capacitats d'aquests sistemes i actualment podem trobar sistemes que integren models PLN de manera ubiqua. Alguns exemples d'aquests models amb els quals interaccionem diàriament inclouen models que determinen la intenció de la persona que va escriure un text, el sentiment que pretén comunicar un tweet o la nostra ideologia política a partir del que compartim en xarxes socials. En aquesta tesi s'han proposats diferents models de PNL que aborden tasques que estudien el text que es comparteix en xarxes socials. En concret, aquest treball se centra en dues tasques fonamentalment: l'anàlisi de sentiments i el reconeixement de la personalitat de la persona autora d'un text. La tasca d'analitzar el sentiment expressat en un text és un dels problemes principals en el PNL i consisteix a determinar la polaritat que un text pretén comunicar. Es tracta per tant d'una tasca estudiada en profunditat de la qual disposem d'una vasta quantitat de recursos i models. Per contra, el problema del reconeixement de la personalitat és una tasca revolucionària que té com a objectiu determinar la personalitat dels usuaris considerant el seu estil d'escriptura. L'estudi d'aquesta tasca és més marginal i en conseqüència disposem de menys recursos per abordar-la però no obstant i això presenta un gran potencial. Tot i que el fouc principal d'aquest treball va ser el desenvolupament de models d'aprenentatge profund, també hem proposat models basats en recursos lingüístics i models clàssics de l'aprenentatge automàtic. Aquests últims models ens han permès explorar les subtileses de diferents elements lingüístics com ara l'impacte que tenen les emocions en la classificació correcta del sentiment expressat en un text. Posteriorment, després d'aquests treballs inicials es van desenvolupar models AP, en particular, Xarxes neuronals convolucionals (XNC) que van ser aplicades a les tasques prèviament esmentades. En el cas de el reconeixement de la personalitat, s'han comparat models clàssics de l'aprenentatge automàtic amb models d'aprenentatge profund la qual cosa a permet establir una comparativa de les dos aproximacions sota les mateixes premisses. Cal remarcar que el PNL ha evolucionat dràsticament en els últims anys gràcies a el desenvolupament de campanyes d'avaluació pública on múltiples equips d'investigació comparen les capacitats dels models que proposen sota les mateixes condicions. La majoria dels models presentats en aquesta tesi van ser o bé avaluats mitjançant campanyes d'avaluació públiques, o bé s'ha emprat la configuració d'una campanya pública prèviament celebrada. Sent conscients, per tant, de la importància d'aquestes campanyes per a l'avanç del PNL, vam desenvolupar una campanya d'avaluació pública on l'objectiu era classificar el tema tractat en un tweet, per a la qual cosa vam recollir i etiquetar un nou conjunt de dades. A mesura que avançàvem en el desenvolupament del treball d'aquesta tesi, vam decidir estudiar en profunditat com les XNC s'apliquen a les tasques de PNL. En aquest sentit, es van explorar dues línies de treball.En primer lloc, vam proposar un mètode d'emplenament semàntic per RNC, que planteja una nova manera de representar el text per resoldre tasques de PNL. I en segon lloc, es va introduir un marc teòric per abordar una de les crítiques més freqüents de l'aprenentatge profund, el qual és la falta de interpretabilitat. Aquest marc cerca visualitzar quins patrons lèxics, si n'hi han, han estat apresos per la xarxa per classificar un text.[EN] In the last years, Deep Learning (DL) has revolutionised the potential of automatic systems that handle Natural Language Processing (NLP) tasks. We have witnessed a tremendous advance in the performance of these systems. Nowadays, we found embedded systems ubiquitously, determining the intent of the text we write, the sentiment of our tweets or our political views, for citing some examples. In this thesis, we proposed several NLP models for addressing tasks that deal with social media text. Concretely, this work is focused mainly on Sentiment Analysis and Personality Recognition tasks. Sentiment Analysis is one of the leading problems in NLP, consists of determining the polarity of a text, and it is a well-known task where the number of resources and models proposed is vast. In contrast, Personality Recognition is a breakthrough task that aims to determine the users' personality using their writing style, but it is more a niche task with fewer resources designed ad-hoc but with great potential. Despite the fact that the principal focus of this work was on the development of Deep Learning models, we have also proposed models based on linguistic resources and classical Machine Learning models. Moreover, in this more straightforward setup, we have explored the nuances of different language devices, such as the impact of emotions in the correct classification of the sentiment expressed in a text. Afterwards, DL models were developed, particularly Convolutional Neural Networks (CNNs), to address previously described tasks. In the case of Personality Recognition, we explored the two approaches, which allowed us to compare the models under the same circumstances. Noteworthy, NLP has evolved dramatically in the last years through the development of public evaluation campaigns, where multiple research teams compare the performance of their approaches under the same conditions. Most of the models here presented were either assessed in an evaluation task or either used their setup. Recognising the importance of this effort, we curated and developed an evaluation campaign for classifying political tweets. In addition, as we advanced in the development of this work, we decided to study in-depth CNNs applied to NLP tasks. Two lines of work were explored in this regard. Firstly, we proposed a semantic-based padding method for CNNs, which addresses how to represent text more appropriately for solving NLP tasks. Secondly, a theoretical framework was introduced for tackling one of the most frequent critics of Deep Learning: interpretability. This framework seeks to visualise what lexical patterns, if any, the CNN is learning in order to classify a sentence. In summary, the main achievements presented in this thesis are: - The organisation of an evaluation campaign for Topic Classification from texts gathered from social media. - The proposal of several Machine Learning models tackling the Sentiment Analysis task from social media. Besides, a study of the impact of linguistic devices such as figurative language in the task is presented. - The development of a model for inferring the personality of a developer provided the source code that they have written. - The study of Personality Recognition tasks from social media following two different approaches, models based on machine learning algorithms and handcrafted features, and models based on CNNs were proposed and compared both approaches. - The introduction of new semantic-based paddings for optimising how the text was represented in CNNs. - The definition of a theoretical framework to provide interpretable information to what CNNs were learning internally.Giménez Fayos, MT. (2021). Natural Language Processing using Deep Learning in Social Media [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172164TESI