The present moment isn't a point — it's a window. Signals from different senses travel different routes and arrive at different times. The brain groups events within roughly 100–300 milliseconds of each other as simultaneous. Events outside that window register as separate.
Two demos below. The first shows what happens as signal delay crosses the binding threshold. The second shows postdiction: the brain inserting sensations retroactively, after the fact, before the window finishes closing.
Signal asynchrony
Signal delay
80 ms
Binding window
220 ms
Three rows: visual signal (blue), binding window region (shaded), auditory signal (amber). When the auditory signal lands inside the window — delay ≤ window — the pair binds into one perceived event. Drag the delay past the window threshold to separate them.
Postdiction: the cutaneous rabbit
Three taps: wrist, wrist, elbow. Watch where the brain places them once all three have arrived.
Three physical taps. The first two land at the wrist; the third at the elbow. After all three arrive, the brain revises. It inserts phantom taps traveling up the arm — sensations on skin that was never touched. They feel as if they happened at the time. The revision is complete before "now" finishes being assembled.