Ambient Occlusion

"Ambient occlusion is a shading method used in 3D computer graphics which helps add realism to local reflection models by taking into account attenuation of light due to occlusion. Ambient occlusion attempts to approximate the way light radiates in real life, especially off what are normally considered non-reflective surfaces.
Unlike local methods like Phong shading, ambient occlusion is a global method, meaning the illumination at each point is a function of other geometry in the scene. However, it is a very crude approximation to full global illumination. The soft appearance achieved by ambient occlusion alone is similar to the way an object appears on an overcast day."

In one of Andy's tutorials on texturing and lighting, he showed and explained the advantages of ambient occlusion materials to do as a separate render. This render would then be combined with the original render, resulting in a much more realistically shaded image.

Here is an example of one frame of my animation without ambient occlusion, with one layer, and then two layers (edited on photoshop):

And here is the ambient occlusion render used to produce this effect:

After experimenting with this method, I think my renders look a lot better with at least one layer of ambient occlusion added to them, and therefore am trying to get all of my animation rendered as ambient occlusion too, although it takes a lot longer to render than my originals. If it does finish rendering, when done, I will probably use After Effects to merge the two types of footage together to achieve the same effect but in video.