Fast subtitles cause superficial reading: evidence from eye movements

Recent research has revealed a negative impact of speed on the reading and comprehension of subtitles in video, with shallower processing of the subtitles and a decrease in comprehension.

While subtitle speed has long been considered as an important parameter in subtitling guidelines, little is known about how it might affect the reading and comprehension of subtitles in video.

To address this question and provide more empirical evidence for subtitling guidelines, we used state-of-the-art eye trackers in Macquarie University’s Multimodal Language Processing Lab to record viewers’ eye movements when watching video with subtitles at different speeds.

We asked our participants – 31 native English speakers – to watch 6 short documentary videos (each about 10 minutes) with subtitles presented at 3 speeds (calculated at characters per second, or cps): 12, 20 and 28 cps. A comprehension test was then used to assess their comprehension of the subtitle content.

We found that viewers’ comprehension decreases as subtitle speed increases, and more so at very high speeds. Eye-movement records also showed that the way viewers process the subtitles and the background video changes as subtitle speed increases. Specifically, viewers read subtitles in a more superficial manner with increasing subtitle speeds, resulting in a text-skimming behaviour with fewer, shorter fixations on the subtitle and more words being skipped. We also found that viewers are not able to read the whole subtitle at faster speeds (around 20% of the subtitle words were not read at 20 cps, and 25% at 28 cps). Fast subtitles also impair viewers’ ability to integrate the content from the background images and the subtitle to gain a comprehensive understanding of the whole video.

The study concluded that subtitle speed below 20 cps is preferable for documentary videos, although this recommended speed needs to be adjusted depending on video complexity and the reading proficiency of the viewers. It also suggests that people might be able to develop effective strategies to cope with fast subtitles with practice or training, which warrants further investigations.