2 things distinguish low stimulation to me
1) no bells and whistles. the less "going on" the better for those times when you need a low stim. activity - try letting lo play with a stuffed dog (they can feel the texture, bite it, squeeze it, etc), a block or 2, things that are not in their face making noises etc - they can control how much they do with it. i also put olivia sitting looking out the window at the trees, birds, etc which fascinates her but it is not too intense...
2) as explained to me by a nurse - WE are what make many things stimulating. if you put lo down with toys (any kind) but leave it to them to decide how to play with it and which ones... then they shoudl be ok - it is when you shake toys at them, interact while they are playing, etdc that the stimulation increases. so the difference is there if you give THEM a squeaky toy to explore VS. you sitting there squeaking that mousy toy at the saying "look at the mouse, BLAH BLAH BLAH"
hope that helps a little