PREFACE

This book highlights the potential of audio-visual input for incidental vocabulary learning by exploring whether words can be learned and retained incidentally through viewing TED-talks and whether its effect could be the same or even better than the wellrecognized written input.This book also addresses questions related to the effectiveness of audio-visual input with different pedagogical treatments，such as embedded second language（L2）captions and repeated TED-talks viewing.Whether incidental vocabulary learning and retention are affected by learner-related factors and item-related factors are also investigated in this book.

Data were collected from 201 English majors from Hainan in their second year at university.A pretest-posttest and within-subject design was adopted.60 target words occurring in six TED-talk videos were examined.Learning gains were measured at threedimensional vocabulary knowledge：form，meaning and use.The results of the study indicated that：① Words can be learned and retained incidentally from viewing TEDtalks；② Written input is effective；however，audio-visual input is more likely to put learners in a better position to gain word knowledge at different aspects；③ Captions and repetition have the potential to increase incidental vocabulary learning；④ Incidental vocabulary learning is mediated by learners'vocabulary size and comprehension proficiency；⑤ Incidental vocabulary learning is also influenced by the frequency of word occurrence and contextual clues in the discourse.

The book ends with a consideration of implications for teaching practice.That is，TED-talk videos are a reliable source of incidental vocabulary learning and video-based activities could be employed in or out of the classroom.It is advisable for teachers to use L2 captions as scaffolding and apply repeated viewing methods in regular classroom teaching.When selecting the videos，teachers should consider the lexical coverage and the materials'difficulty level.The frequency of the new word occurrence and whether contextual clues surround new words are helpful for meaning inference should also be taken into consideration.

Wu Yan

August 17，2023