This study aimed to investigate the relationship between lexical coverage and TV viewing comprehension. Previous studies have indicated that 95% to 98% of lexical coverage may be needed for reading comprehension (Hu & Nation, 2000). To understand informal listening passages, lower coverage figures (95%-90%) may suffice. However, no study has researched the lexical coverage needed to understand audiovisual texts. We adopted a counter-balanced within-participants design, in which 5%, 10%, or 20% of the words in four 2-min documentaries were replaced with nonwords. Native and non-native speakers of English participated in this study. Results showed that comprehension scores decreased as lexical coverage decreased; comprehension at 100% coverage was significantly higher than 90% and 80% in the two groups; and optimal adequate comprehension is achieved with an optimal lexical coverage of 95%, whereas minimal adequate comprehension is reached with a minimal lexical coverage of 80%.
