These adaptations made it possible, not only to produce phonetic gestures, but also to coarticulate them so that they could be produced rapidly. The Locus concept Formant transitions for a variety of vowels point to the same locus for a given place of articulation. The extrapolated formant transitions converge on a single point. This is the invariant Gesture. There is actually no such thing as an invariant locus.
Listeners perceive the consonants in terms of discrete articulatory gestures.
The use their speech mode of perception. Birds trained in Exp I, extended place categorization to novel contexts. There is no speech mode specific to humans. There is no invariant locus for place of articulation. It does not seem likely that here there are invariant gestures.