The effects of blurred vision on auditory-visual speech perception in younger and older adults

Speech understanding is improved when the observer can both see and hear the talker. This study compared the effects of reduced visual acuity on auditory-visual (AV) speech-recognition in noise among younger and older adults. Two groups of participants performed a closed-set sentence-recognition task in one auditory-alone (A-alone) condition and under three AV conditions: normal visual acuity (6/6), and with blurred vision to simulate a 6/30 and 6/60 visual impairment. The results showed that (1) the addition of visual speech cues improved speech-perception relative to the A-alone condition, (2) under the AV conditions, performance declined as the amount of blurring increased, (3) even under the AV condition that simulated a visual acuity of 6/60, the speech recognition scores were significantly higher than those obtained under the A-alone condition, and (4) generally, younger adults obtained higher scores than older adults under all conditions. Our results demonstrate the benefits of visual cues to enhance speech understanding even when visual acuity is not optimal.