...or is it just me?

I hope you'll forgive my fumbling, but I've leapt straight from P4 to P6 and so am climbing a steep learning curve when it comes to the shaders and nodes of the Firefly render engine (and much else besides ;-)).

Anyway, so far my experience with Ambient Occlusion is that it takes no account of light direction. It seems that if two surfaces are close by then they darken one other based on their proximity alone, as if the "occlusion" in question is for some mysterious all-round light source (that plays no other part in the scene).

Thus, in a scene with just one light, surfaces are darkened by the proximity of nearby surfaces that do not actually occlude the rays from that light.

In real life, a bright surface placed near a second surface will actually brighten that second surface due to diffuse reflection of light (what 3D programs call 'radiosity'); yet the opposite seems to happen with Ambient Occlusion.

Am I missing something?

You have more or less answered your own question, AO is intended to simulate the occlision of light from an all round (ambient) light source. Object seperation is a natural factor in accounting for the amount of light the a surface is exposed to, but it is intended only to simulate the shadowing effect. To fake radiosity or reflected light effects, try using the Gather node. Bill

Thanks Bill. So it is just me. :-) I've been messing with the Gather node but the results are inconsistent so far. The same Gather node settings used on various materials/objects ends up with some wildly different interactions. Incidentally (if you'll excuse the pun) I tried attaching an Ambient Occlusion node to the Ambient channel of a material and ended up with a surface that projected 'light' into the scene. Of course, it did so in a strange way and Poser fell over, but it does give the hint that someone who knows what they are doing could end up with something akin to an area light...

"but it does give the hint that someone who knows what they are doing could end up with something akin to an area light..." That's basically what the gather node does. It simulates radiosity-like color bleeding, and can make an object's material appear to be casting light. Be warned though, it takes a LOOONG time to render good results using it. The AO function, although usable with standard lights, should really only be used on a diffuse IBL light... It works in tandum with IBL to simulate a "single bounce" GI setup, and the soft area-type shadows that it produces. Much faster than calculating true radiosity, or GI that calculates 2 or more light bounces.

Attached Link: http://fnproductions.net/graphics/tutorials/poser6