"facial expression" usually suggests an expression conveying emotion, "facial distortion" tends to sound extreme and unnatural, and "facial change" seems a bit vague. I think the problem with "facial" is that it refers to the whole face, including, for example, the eyes, which have nothing to with the production of speech. It also refers only to the visible face, ignoring the position of the tongue, for example, which is crucial to speech production.
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