In this talk, I will present a lip tracking method that can be used to study speech articulation and confront articulatory data with acoustic evidence of stop lenition. While earlier motion capture methods required special equipment, new developments were made in recent years that allow for optical lip tracking based on internet camera recordings. I will discuss two of my studies that use this method and implementations presented by other authors that confirm its validity for segmental research.
First, I will show that looking at lip aperture measurements helps determine the contexts and extent of /p b/ weakening in Canary Islands Spanish. Lip tracking data reveals that:

– stop lenition is limited to postvocalic position
– stop lenition Is blocked in derived postvocalic position
– there are asymmetries in prosodic effects when compared to acoustics.

The second study looks at final /t d/ deletion in American English. Here, the discrepancy between articulation and acoustics is under analysis and lip movement data is used to test the completeness of the process. /t d/ trapped in between bilabials are used to track lip aperture changes that may be semblant of incomplete pronunciations. Ultrasound data of tongue blade movements is used to confirm lip trajectories as proxies of alveolar gestures.