Television captions for hearing-impaired people: a study of key factors that affect reading performance.

Closed captions are broadcast with television programs for special-needs viewers such as hearing-impaired people. We examined how caption presentation rate, small amounts of induced dioptric blur, and English learned as a second language affect the reading performance of good readers. Thirty-two college graduates with normal hearing and vision, half of whom learned English as a second language, read television captions that consisted of white capital letters equivalent in size to 20/92 Snellen letters on a black background. Text was presented at rates of 55, 120, and 216 words/min. Lenses of 0, 0.5, 1.0, or 1.5 diopters (D) were worn over the person's best refractive correction. The fastest text rate and small amounts of blur significantly disrupted reading performance. People who learned English as a second language were hindered more by presentation rate than by dioptric blur. Surprisingly, people with refractive errors (even though they were optically corrected) were hindered less by induced blur than were people with normally clear vision.