The Effect of Simulated Cataracts on Speech Intelligibility

The classic study of Sumby and Pollack (1954) demonstrated that visual information aided speech intelligibility under noisy auditory conditions. Their work showed that visual information is especially useful under low signal-to-noise ratios where the auditory signal leaves more margins for improvement. We investigated whether simulated cataracts interfered with the ability of participants to use visual cues to help disambiguate the auditory signal in the presence of auditory noise. Speech intelligibility was tested under an auditory only condition and two visual conditions: normal vision and simulated cataracts. The light scattering effects of cataracts were imitated using cataract-simulating filters. Participants wore blacked-out glasses in the auditory only condition and lens-free frames in the normal auditory-visual condition. Individual sentences were spoken by a live speaker in the presence of prerecorded four-person background babble set to a speech-to-noise ratio of -16 dB. The speaker was trained to match the rate, intensity and inflections of a prerecorded audio track of everyday speech sentences. The speaker was blind to the visual conditions of the participant to control for bias. Participants' speech intelligibility was measured by the accuracy of the written account of what they believed the speaker to have said. Relative to the normal condition, speech intelligibility was poorer when participants wore simulated cataracts suggesting that cataracts may interfere with both visual and auditory perception.