Articulography

Electromagnetic midsagittal articulography is a transmitter system in which very small receivers, placed at various points (e.g. lips, teeth, parts of the tongue), send movement signals which are accurately plotted as articulatory trajectories, using a system of absolute coordinates.

Comment
This technique can be used to show that vertical tongue body movements during the articulation of a consonant are affected by such factors as voicing and the nature of adjacent vowels.

Link
Utrecht Lexicon of Linguistics