Your question about losing your humanity is a deep one, it begs an exploration of human identity, and how much difference we can tolerate. I just read a trilogy that I borrowed from a friend by John Skalzi. The first was "Old Man's War", or something like that. Here old people volunteered to join the military. Their conciousness would be lifted from their aging bodies and somehow transplanted into new enhanced bodies. 

Treadgar

well, it seems an experiment was done a while ago.

they took mice < who have bi chromatic vision- I think, yellow/blue? > and they added the gene for the red colour receptor us primates have,

it worked, when the mice were grown they could see red as well- it seems that the mouse brain organized itself to use the extra ability

 

that means that ith a bit of embryo tweaking you could give a human the colour receptors for the extra visual colours that birds can see, or insects.

near IR and UV vision anyone?

Treadgar