A central focus of my dissertation research is an investigation of how both auditory and visual speech perception can constrain articulatory patterns, and how phonological systems are shaped by (and optimized for) both auditory and visual perceptibility.
Building on work in articulatory variability in the Northern Cities Vowel Shift, Youngah Do and I have found that variants of fronted /ɔ/ that retain their lip rounding are less likely to be misperceived as /ɑ/ than variants that are produced with unround lips. This finding suggests that speakers may prefer round over unround variants in order to maximize perceptibility in both the auditory and visual domains.
This argument is further supported by findings from my 2018 dissertation, which show that speakers from Chicago tend to preserve the lip rounding gesture for /ɔ/ as it undergoes fronting, and that these speakers optimize their speech for visual perceptibility by increasing the degree of lip rounding for /ɔ/ in careful speech contexts. In some cases, this increase in rounding is not associated with an increase in acoustic distance from /ɑ/, suggesting that articulatory patterns can be optimized for visual perceptibility alone.
Havenhill, Jonathan. 2018. Constraints on articulatory variability: Audiovisual perception of lip rounding. Doctoral dissertation, Georgetown University. [PDF]
Havenhill, Jonathan, and Youngah Do. 2018. Visual speech perception cues constrain patterns of articulatory variation and sound change. Frontiers in Psychology 9.728. doi:10.3389/fpsyg.2018.00728.
Havenhill, Jonathan. 2018. Audiovisual cue enhancement in the production and perception of the cot-caught contrast. Paper presented at the 47th New Ways of Analyzing Variation (NWAV47), New York, NY. [PDF]