On the legibility of TV subtitles for the elderly and partially sighted

We have investigated the influence of character size, contrast and/or luminance and presentation time on the legibility of subtilles for a group of nonnally sighted young and elderly subjects and a group of visually impaired subjects. For this purpose, pairs of text lines were presented on a TV monitor. For the partially sighted the tex.t lines were presented against a plain background and in the case of the normally sighted a comparison was made between the legibility of text lines against a plain background and text lines presented against a videoscene background. In the first experiment all subjects had to read aloud and could determine the duration of the presentation of the text lines themselves. Reading rate was measured as a function of character size and contrast and/or luminance. In the second experiment the text lines were presented for a fixed length of time. The subjects, reading silently, were asked to indicate whether they had enough time to read through the text lines. The experimental results clearly show that reading subtitles against a video background as compared to reading text lines against a plain background is slightly more difficult for the elderly. In the case of the partially sighted subjects, character size and contrast and/or luminance are found to have a marked effect on the reading rate.