Overstimulation is a little misunderstood, I find. For instance, baby lying on the floor, having one rattled toy after another shown can be quite overstimulating quite quickly. Babies learn best in a state of quiet observation, even when there is a LOT of hubbub. For instance, being in a wrap or buggy or bus in quite a loud environment is rarely overstimulating when there is motion.
So when baby is expected to do something, like smiling, laughing, playing with a toy, having sensory input, THAT can be OS after a wee while (though both mine could do that for ages).
When NOT expected to do something, but being on the move, baby will not be overstimulated.
The womb is VERY loud and baby moves in there all the time. After coming out and for the first six months or so, that stillness is extremely disconcerting for babies, hence the invention of wraps, rock and plays, white noise, vibrating bouncy chairs, taking babies for long car- or bus rides, etc. Sometimes, we think a baby is OS, when in fact, baby is EXTREMELY bored and hasn't been juggled around enough.
