IMO it makes the caster aware of and able to distinguish all movement in the radius.
i.e.
without the spell, standing in the woods, you hear all sorts of rustling in the ground cover and leaves fluttering in the breeze.
With the spell, you feel every leaf and twig moving in the breeze, feel the small fieldmouse searching in the ground cover for bugs, feel all the bugs moving around, but also feel the goblin slowly stalking up through the brush toward you, and your friend joe stalking the goblin. . .
I play it makes you aware of all motion in the radius, and the shape of what's moving. . .I wouldn't allow you to distinguish the goblin from your friend joe, unless it's obvious like the goblin is 4' tall and joe is 6' tall, but you'd definitely know where the two moving humanoids are regardless.