Stéphan Tulkens


Orthographic Codes and the Neighborhood Effect: Lessons from Information Theory
Stéphan Tulkens | Dominiek Sandra | Walter Daelemans
Proceedings of the Twelfth Language Resources and Evaluation Conference

We consider the orthographic neighborhood effect: the effect that words with more orthographic similarity to other words are read faster. The neighborhood effect serves as an important control variable in psycholinguistic studies of word reading, and explains variance in addition to word length and word frequency. Following previous work, we model the neighborhood effect as the average distance to neighbors in feature space for three feature sets: slots, character ngrams and skipgrams. We optimize each of these feature sets and find evidence for language-independent optima, across five megastudy corpora from five alphabetic languages. Additionally, we show that weighting features using the inverse of mutual information (MI) improves the neighborhood effect significantly for all languages. We analyze the inverse feature weighting, and show that, across languages, grammatical morphemes get the lowest weights. Finally, we perform the same experiments on Korean Hangul, a non-alphabetic writing system, where we find the opposite results: slower responses as a function of denser neighborhoods, and a negative effect of inverse feature weighting. This raises the question of whether this is a cognitive effect, or an effect of the way we represent Hangul orthography, and indicates more research is needed.

Embarrassingly Simple Unsupervised Aspect Extraction
Stéphan Tulkens | Andreas van Cranenburgh
Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics

We present a simple but effective method for aspect identification in sentiment analysis. Our unsupervised method only requires word embeddings and a POS tagger, and is therefore straightforward to apply to new domains and languages. We introduce Contrastive Attention (CAt), a novel single-head attention mechanism based on an RBF kernel, which gives a considerable boost in performance and makes the model interpretable. Previous work relied on syntactic features and complex neural models. We show that given the simplicity of current benchmark datasets for aspect extraction, such complex models are not needed. The code to reproduce the experiments reported in this paper is available at


WordKit: a Python Package for Orthographic and Phonological Featurization
Stéphan Tulkens | Dominiek Sandra | Walter Daelemans
Proceedings of the Eleventh International Conference on Language Resources and Evaluation (LREC 2018)

From Strings to Other Things: Linking the Neighborhood and Transposition Effects in Word Reading
Stéphan Tulkens | Dominiek Sandra | Walter Daelemans
Proceedings of the 22nd Conference on Computational Natural Language Learning

We investigate the relation between the transposition and deletion effects in word reading, i.e., the finding that readers can successfully read “SLAT” as “SALT”, or “WRK” as “WORK”, and the neighborhood effect. In particular, we investigate whether lexical orthographic neighborhoods take into account transposition and deletion in determining neighbors. If this is the case, it is more likely that the neighborhood effect takes place early during processing, and does not solely rely on similarity of internal representations. We introduce a new neighborhood measure, rd20, which can be used to quantify neighborhood effects over arbitrary feature spaces. We calculate the rd20 over large sets of words in three languages using various feature sets and show that feature sets that do not allow for transposition or deletion explain more variance in Reaction Time (RT) measurements. We also show that the rd20 can be calculated using the hidden state representations of an Multi-Layer Perceptron, and show that these explain less variance than the raw features. We conclude that the neighborhood effect is unlikely to have a perceptual basis, but is more likely to be the result of items co-activating after recognition. All code is available at:


A Short Review of Ethical Challenges in Clinical Natural Language Processing
Simon Šuster | Stéphan Tulkens | Walter Daelemans
Proceedings of the First ACL Workshop on Ethics in Natural Language Processing

Clinical NLP has an immense potential in contributing to how clinical practice will be revolutionized by the advent of large scale processing of clinical records. However, this potential has remained largely untapped due to slow progress primarily caused by strict data access policies for researchers. In this paper, we discuss the concern for privacy and the measures it entails. We also suggest sources of less sensitive data. Finally, we draw attention to biases that can compromise the validity of empirical research and lead to socially harmful applications.


Using Distributed Representations to Disambiguate Biomedical and Clinical Concepts
Stéphan Tulkens | Simon Suster | Walter Daelemans
Proceedings of the 15th Workshop on Biomedical Natural Language Processing

Evaluating Unsupervised Dutch Word Embeddings as a Linguistic Resource
Stéphan Tulkens | Chris Emmery | Walter Daelemans
Proceedings of the Tenth International Conference on Language Resources and Evaluation (LREC'16)

Word embeddings have recently seen a strong increase in interest as a result of strong performance gains on a variety of tasks. However, most of this research also underlined the importance of benchmark datasets, and the difficulty of constructing these for a variety of language-specific tasks. Still, many of the datasets used in these tasks could prove to be fruitful linguistic resources, allowing for unique observations into language use and variability. In this paper we demonstrate the performance of multiple types of embeddings, created with both count and prediction-based architectures on a variety of corpora, in two language-specific tasks: relation evaluation, and dialect identification. For the latter, we compare unsupervised methods with a traditional, hand-crafted dictionary. With this research, we provide the embeddings themselves, the relation evaluation task benchmark for use in further research, and demonstrate how the benchmarked embeddings prove a useful unsupervised linguistic resource, effectively used in a downstream task.