Visual Speech Benefit in Clear and Degraded Speech Depends on the Auditory Intelligibility of the Talker and the Number of Background Talkers.
Catherine L Blackburn, Pádraig T Kitterick, Gary Jones and 2 others
PMID 30909814WHAT IT FOUND
Seeing the talker's mouth improved word understanding, but the benefit was not fixed.
It varied with background talkers and talker intelligibility. In Experiment 2, degraded speech gave more benefit overall, and a hard-to-understand talker gave more benefit than a clear talker for clear speech.
Key findings
01Seeing the talker improved speech reception thresholds compared with hearing alone, meaning participants could understand words in more background noise when the talker was visible.
02The number of background talkers significantly affected visual benefit, but in Experiment 1 there was no overall significant difference in benefit between clear and vocoded speech.
03In Experiment 2, visual benefit was larger for vocoded speech than clear speech, and the least intelligible talker gave more benefit than the most intelligible talker for clear speech.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The participants were normal-hearing students and staff, not cochlear implant users or people with hearing loss. Vocoded speech simulated only the loss of temporal fine structure and filtering into eight bands, not other difficulties faced by cochlear implant users. The adaptive procedure set performance at 50% correct, so the study measured benefit at equalised difficulty rather than at a fixed noise level. Seven participants' audio-only vocoded tracks for the least intelligible talker did not converge, so Talker 4 data were excluded from some vocoded analyses. The sample was 24 participants per experiment, and the study used short IEEE sentences in a laboratory booth, so everyday conversation was not tested. The signal detection model did not fully predict the pattern of visual benefit, so the underlying integration process remains uncertain.
The easy way to misread this
Do not conclude that this study proves seeing the talker helps cochlear implant users in everyday conversations. The participants had normal hearing, and vocoded speech simulated only some aspects of implant hearing, not all difficulties faced by implant users.