[shawnz]

Visually we perceive 2 dimensions (i.e. you can't see behind things), the third is just something we imagine as being closer to or further from the camera without being able to directly perceive it. So maybe the fourth would be the same, but just orthogonal to the third.

[Izkata]

> the third is just something we imagine as being closer to or further from the camera without being able to directly perceive it.

Er no, we do perceive the third due to having stereoscopic vision.

[infogulch]

You're right that our vision gives us a 3D perception, but only in the same way that a surface in a 3D space may be stretched and squashed and even have discontinuities, but is still fundamentally 2-dimensional, it has no volume. That still doesn't give us volumetric vision.

If you had true 3D/volumetric vision, you would find painting over objects aesthetically pointless, because you see behind not just the paint, but also through every layer and sub-component of the object all at once.

For example, most "3D" video games would seem very strangely empty and hollow to a being that could perceive volumetric space directly, because games are implemented by manipulating (many) fundamentally 2D surfaces in 3D space. This implementation technique works to suspend our disbelief because we don't see 3D volumes, we see 3D surfaces.

I would also be very keen to know if the human brain could directly perceive a volumetric space.

[shawnz]

Stereoscopic vision doesn't let you see a whole 3D scene at once, it just gives some clues as to how far away things are in the 2D scene which you can perceive visually.