How do animal perceive distances with their eyes and ears I am studying how animals (including the human beings) can perceive distances thanks to their eyes and their ears. I am focusing on the fact that they always go in pairs: two eyes, two ears, etc.
About the sight, I think our eyes use the parallax. But is this enough? Is this the only way we can perceive distances with them?
About the sounds, I think it is merely by interferometry, but I am not convinced, because the distances between our ears and the wavelength are not always comparable to one another.
What do you think about it?
Thanks in advance,
Isaac
 A: With vision depth is determined by parallax.  This largely works for objects out to 100m or less.  Depth beyond that distance is assessed by familiarity with these objects, say large mountains or vistas, and experience with them.  
Depth with hearing is determined by two means.  A tone which is perceived louder in one ear than the other is usually perceived as having a direction based on that.  For lower frequency sounds phase differences between left and right auditory perception can be used by the brain to detect angular direction relative to the facial direction.  
Some species of whales are thought to generate a mental map of the ocean, where a blue whale in the Atlantic maps the outlay of the ocean bottom and coasts through echo location.  Clearly this indicates a huge amount of neural processing which uses these acoustical data.  Dogs generate maps of their immediate world through olfactory means.  Life forms generate maps of their world by a variety of means.
A: Adding to Lawrence's answer, apart from the monocular cues like depth from shading, lighting, haze, geometrical structure and familiarity of objects, you also have binocular cues from the eye motor convergence system (eyes point at the spot you are looking at in 3d space) as well as the feedback from the lens focusing system.
All of these systems work together when you look at objects in the real world, but in for example 3d movies and tvs only some are active, which can cause various sorts of dizziness or headache among viewers.
Interestingly viewing plain old 2d photos of 3d objects/worlds does not infer this sickness at all..
With regards to hearing, apart from loudness and phase the auditory system also uses timing of onset, this obviously relates to phase discrimination depending on the audio frequency and size of the head. Furthermore, the spectral filtering of the signals at both ears is shaped by the asymmetrical shape of the outer ears, this allows the auditory system to gauge sound localization in front of, behind, above and below. Monaural cues include, as with vision, familiarity of certain sounds or speakers and how these sounds degrade by passing through air.
Several hundred million years of evolution has been pretty good at extracting every bit of useful information from all our senses :)
