(A) Subjects optimized the energetic cost of their movements in the non-delayed pong game by hitting the ball at the peak velocity of the paddle. (B) In adaptation trials, there was a continuous effort towards recovering the energy optimal policy by reducing the difference between the time of the peak velocity of the paddle and the time of the impact (C) In the delayed pong, visual and proprioceptive measurements were different at the time of collisions. Hence, sensory integration at events caused a misperception of the paddle’s mass. Mass modifier is the difference between the actual mass and the perceived mass. Depending on the timing of the hits, the mass modifier can have three categorical values: a hit around leads to a negative mass modifier (), a hit at () makes the mass modifier to be zero and for a hit around (), the mass modifier is positive. (D-F) Left panels show the average velocity profile of the hand and the paddle during the last five minutes of adaptation for three individual subjects, one from each possible outcome category. The vertical dashed line represents the average time of the hit in the pong game. Right panels show the adaptation effects on the reaching movements. Error bars represent one standard error of the mean. These results are consistent with the hypothesis that mass estimation occurs at discrete events. (G) Effective mass of the manipulandum in each direction. Each plot is centered on the average position of the hits for the corresponding group. Subjects in the LPR group played with a heavier paddle than the LPL group. In addition, the mass modifier is proportional to the mass of the paddle itself. Gray areas represent 95% confidence intervals.