Fortunately we've got the full system because even under ideal conditions nobody's actually ever been intelligent at all times and we need the momentum from that full system to resume in an intelligent direction after an upset when it's not all at its best.
The whole point of humans is the way we process the input. Every life form out there receives sound vibrations and has photons hitting their body all the time, not everyone uses that information in the same way or at all. That plus natal reflexes and hardcoded assumptions
you could argue that our input (senses) entirely define the output (thoughts, muscle movements, etc)