In order to know and judge the influence on expression of the facial muscles, I have produced contractions of the latter with electrical currents. I always started with the face in repose, when it showed internal calm; the gaze of my subject was initially fixed and directed forward.

First I put each of the muscles into isolated contraction, on one side and then both sides of the face at the same time; then, progressing from the simple to the composite, I combined these isolated muscle contractions in all the variations possible, by making the different named muscles contract, two by two and three by three.

I will describe concisely, in the following paragraphs, the principal facts that have come to light by these isolated contractions and by the combined contractions of the muscles of the face.

Isolated contractions of the muscles of the face

The experimental study of isolated contractions of the muscles of the face shows that they are either completely expressive, incompletely expressive, expressive in a complementary way, or inexpressive.

Isolated contractions that are completely expressive

There are muscles that produce an expression of their own by their isolated action.

At first glance this assertion appears paradoxical. Although a small number of muscles have been accorded a special influence on facial expression, one would at the same time imagine that all expression depends on the harmonious working and synergy of at least several other muscles.