Although Helmholtz was primarily concerned to show that “our judgments as to the direction of the visual axis are simply the result of the effort of will involved in trying to alter the adjustment of the eyes” (2005 [1924]: 205–06), the evidence he adduces also implies that efferent signals play a critical role in our perception of stability in the world across saccadic eye movements. In the next section, we trace the influence of this idea on theories in the 20th century.