: Of course, there are lots of animals on Earth with more than 2 eyes, but I
: don't thnik any natural animal has an odd number.
Actually, some lizards have a third eye located in about the position of the Pfhor 3rd eye. Indeed, even humans have a vistigial 3rd eye - the pineal gland - which is now embedded deep within the brain. This third eye never provided much in the way of visual information, but rather it responded to changes in ambient light, which modulated hormone output.
Now as far as the Pfhor are concerned, there actually could be some advantages to trinocular vision. Not only would a 3rd eye enhance the accuracy of depth perception, but it would provide a significant boost to the sense of vertical perspective. Think of triangulation - the process by which a radio source can be found uniquely by using 3 antennas. With 2 antennas, you can only determine position within a plane and distance is inaccurate. The 3rd antenna adds elevation and significantly improves distance accuracy, while eliminating ambiguity. With your 2 ears, you can sense direction (but not front or back), but you cannot ascertain elevation without other clues. With vision it is different because you have full 2D spatial information from each eye. By using a significant amount of cortical image processing, you are albe to uniquely locate points in space. With a third eye, however, the need for image processing would be significantly reduced and the accuracy of point localization would be enhanced. This could have never evolved in the bilateral human brain. I wonder if the Pfhor brain is trilobar.
