Suzi Park and Hyopil Shin. 2019. This paper investigates the notion of instability in word embeddings, primarily focused on the Korean language, by analyzing the effects of instability on several tasks using word level, character level, and sub-character level embeddings. Korean has a complex morphological system and is written at units smaller than that of a single character, making it optimal for comparing the three types of embeddings. We first carry out several intrinsic evaluations such as word similarity and analogy tests, as well as an extrinsic evaluation of the embeddings on the task of sentiment analysis. These results show that sub-character embeddings outperform the other two types, obtaining both higher and more consistent results, especially when the corpus size is large. Based on these findings, our hypothesis is that embeddings trained on smaller units and larger corpora would also be a better choice in terms of stability. To investigate this, we implemented two stability tests, looking into cosine similarity standard deviations and intersection of nearest neighbors among models. Our findings demonstrate that indeed, the smaller the embedding unit and the larger the corpus, the more stable the embedding type is. Importantly, our results illustrate the necessity of taking instability into consideration when using word embeddings within a given experiment.

The present study investigated the underlying cognitive mechanism of the truth-value validation process of Korean comparative structure sentences. The brain and behavioral response of 15 Korean native speakers were recorded and analyzed during the processing of the comparative sentences with 4 conditions manipulated by the frequency of the predicate (big or small) and the truth-value(true or false). The behavioral results (i.e. judgment time and accuracy) showed that only the effect of the predicate's frequency was significant. However, in the ERP, the predicate's frequency effect and the truth-value effect were reflected in early N400 component(250-400ms) as well as the positivity effect in 400-600ms by the truth-value factor. The immediacy of the truth-value validation and the functional interpretation of N400 related to the truth-value were discussed in overall.