Hi I'm new here but take a look at this:

Magnetic fields
The perception of magnetic fields by migratory birds has been suggested to be light dependent.[30] Birds move their head to detect the orientation of the magnetic field,[31] and studies on the neural pathways have suggested that birds may be able to "see" the magnetic fields.[32] The right eye of a migratory bird contains photoreceptive proteins called cryptochromes. Light excites these molecules to produce unpaired electrons that interact with the Earth's magnetic field, thus providing directional information.[33][34] (http://en.wikipedia.org/wiki/Bird_vision)

So that means that magnetic fields maybe are a visible sense.

Nice information dive.

Scio, I vote that "noisy" be reserved for equiptment. It just doesn't look right as something that an organic creature would see, but it's definitely a possible problem with digital.

And I thought that picture looked familiar...

Question, will visual overlay be permanently present, togglable, or will it be a 1st Person/3rd Person distinction?

Touch overlay: Underground is simple enough. If your face is pressed against dirt, toggle limited echolocation.

Now, for regular touch, I vote we have a box or shard or whatever in some corner of the screen that opens up whenever you examine sommit. This will contain text as nessicary, as well as a few visual clues. This should help speed up the recognition procces on the players part. Show a little orb in the shard/box. If it's cold, it'll turn blue. If it's hot, it'll turn red. If it's smooth, it'll be a perfect circle. If it's rough, it'll be grainy and jagged. If it's sharp, it'll grow spikes.

Silly idea, I know, but it might cut off a few seconds of time and help alleviate the immersion fracture text tends to bring.

Wait a second. I don't think excessive sensory overlay is a good idea. So smell should also be in text.
Also, if we have a deeply underground creature without echolocation, it might well be the earlier mentioned newspaper read, with your screen a page saying,
Smells food! It's a Pinercalosaurus!
Feels traction from racing across the cave floor
No, pain! Got stabbed by stalagmite!
Hears scream of Pinercalosaurus
Closing in
Crunches on tasty Pinercalosaurus
Sound: cave moving!
Pain while dying by falling rocks

Sense Smell
organ Nasal organ (may be something else, I hear cats can smell through the roof of their mouth)
render method text displaying smells (smells...) with low sensory, if the smell sense is stronger, they can click a "track" button under the text and a trail of light appears which they can follow
levels weak smell (only text) slightly stronger (text and very faint tracking trails) strong smell (text and bright tracking trails)

Smell is not only used for tracking.

Maybe:
1. Chaotic text
2. 1+color trails
3. 2+trails made of text

why? It's already fine. we don't need trails of text because while following a colour trail, you would see text in the smell text.

for smell, what if we have small buttons of different colors that you can click to smell for certain things. For example we can click on a certain colored button (possibly in the shape of a shard) and then a cloud trail will appear matching the color of the button, leading the player to what you are looking for. Think of it like this: All the player sees is blackness, but then if you want to look only for food you click a green shard (or whatever color will be for food) located somewhere on the screen and then cloud trails leading to possible food sources appear, they will become thicker as you get closer to the source. What do you guys think?