Who has never been up against technical or computer science instructions where the authors have used different terms to describe the same functions or elements? We find the same occurrence in the theory of piano technique even though in this case it has nothing to do with negligence, but rather a lack of knowledge concerning the works of other authors.
Also called vertical vibrations or motor impulses*. This term corresponds to an alternating between placing and removing the motor apparatus on the keyboard - see Neuhaus’ bridge and crane. The frequency of this movement is very rapid, but the vertical vibrations of the arm are extremely small.
*Czesław Sielużycki - “The pianist’s hand” p. 261 and 305-306, Polish Music Edition, Cracow, 1982