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There is emerging evidence that collocation use plays a primary role in determining various dimensions of L2 oral proficiency assessment and development. The current study presents the results of three experiments which examined the relationship between the degree of association in collocation use (operationalized as t scores and mutual information scores) and the intuitive judgements of L2 comprehensibility (i.e. ease of understanding). The topic was approached from the angles of different task conditions (Study 1), rater background (first language or L1 vs. second language or L2) (Study 2) and cross-sectional vs. longitudinal analyses (Study 3). The findings showed that: (1) collocation emerged as a medium-to-strong determinant of L2 comprehensibility in structured (picture description) compared to free (oral interview) oral production tasks; (2) with sufficient immersion experience, L2 raters can demonstrate as much sensitivity to collocation as L1 raters; and (3) conversational experience is associated with more coherent and mutually-exclusive combinations of words in L2 speech, resulting in greater L2 comprehensibility development.

Label-specific topics can be widely used for supporting personality psychology, aspectlevel sentiment analysis, and cross-domain sentiment classification. To generate labelspecific topics, several supervised topic models which adopt likelihood-driven objective functions have been proposed. However, it is hard for them to get a precise estimation on both topic discovery and supervised learning. In this study, we propose a supervised topic model based on the Siamese network, which can trade off label-specific word distributions with document-specific label distributions in a uniform framework. Experiments on realworld datasets validate that our model performs competitive in topic discovery quantitatively and qualitatively. Furthermore, the proposed model can effectively predict categorical or real-valued labels for new documents by generating word embeddings from a labelspecific topical space.

Abstract.As communication between countries becomes increasingly frequent and international trades as well increase rapidly, English as a world common language is useful for assisting countries to communicate with each other. At the same time, the number of people in demand of second language teaching of English is also increasing exponentially. In the development process of second language teaching, there are various theories throughout history, either repellent or similar. Among them, the linguistics memetics is an innovative direction to do studies in applied linguistics in recent years. From the perspective of memetics, memes are deemed as cultural transmission unit, because memes can spread through imitation, therefore, language as one of the most important carriers for the transmission of memes takes an important position.The purpose of this paper is to introduce the theory of memetics to the area of second language teaching, thus to speed up the reform of second language teaching modes.