Towards an open-domain chatbot for language practice
Gladys Tyen, Mark Brenchley, Andrew Caines, Paula Buttery
Abstract
State-of-the-art chatbots for English are now able to hold conversations on virtually any topic (e.g. However, existing dialogue systems in the language learning domain still use handcrafted rules and pattern matching, and are much more limited in scope. In this paper, we make an initial foray into adapting opendomain dialogue generation for second language learning. We propose and implement decoding strategies that can adjust the difficulty level of the chatbot according to the learner's needs, without requiring further training of the chatbot. These strategies are then evaluated using judgements from human examiners trained in language education. Our results show that re-ranking candidate outputs is a particularly effective strategy, and performance can be further improved by adding sub-token penalties and filtering.