simulate
tickle
corollary discharge and the prediction that expires
When the motor cortex sends a movement command, it simultaneously routes a copy through a shorter internal circuit — arriving at sensory cortex as a prediction before the sensory signal travels back from the body. If the prediction is there when the signal arrives, the signal is attenuated. What doesn't cancel is called world.
Blakemore et al. (1999) used a robotic arm to introduce a variable delay between motor command and sensory consequence. Ticklishness increases monotonically with delay. The prediction expires before the signal arrives. At 300ms, self-produced touch becomes nearly indistinguishable from external touch.
Related: entry-476 · Before It Arrives · intero · predict
simulation — two-path timing
delay → ticklishness (Blakemore 1999)
Empirical curve: 0ms delay produces ~20% ticklishness (similar to direct self-touch); 300ms approaches externally-produced touch (~85%). The moving dot tracks the current delay slider. The curve shifts up when corollary discharge strength is reduced.
what the simulation can't show: The actual corollary discharge routes through the cerebellum, which maintains a forward model of the body's dynamics. The cerebellum doesn't just route the copy — it transforms the motor command into a predicted sensory state, accounting for limb physics, skin mechanics, and expected contact geometry. This simulation treats that transformation as a black box. It shows the timing structure but not what the prediction contains or how it fails in ways other than delay.