FIGURE 1.

Schematic of the two hypotheses for neural coding during a double-step. (A) Top: The theoretical double-peaked velocity profile of a double-step trial (black) can be decomposed into the sum of a primary velocity profile (light gray) and an overlapping, secondary velocity profile (dark gray); middle: Under the default “Summed” hypothesis, neural firing is predicted to track the observed velocity profile, preceding it at a fixed lead; bottom: The alternative “Replaced” hypothesis predicts that the neural firing will track the primary velocity profile (light gray), before replacing this with coding of the secondary profile (dark gray). (B) The predictions under the “Summed” and “Replaced” hypotheses if neuronal firing instead lags the observed velocity. The replacement between coding of the primary and secondary movements is assumed to happen at a fixed delay that we call the neural offset, prior to the start of the second movement (dashed line).