Jamie_L

Actually, when you really get into the physics of how material objects interact (especially relevant to touch, but also to other senses) is the fact that the atoms in our bodies consist of mostly empty space. The particles that make up the atoms in our bodies don't really contact the particles that make up the other object. It's all an interaction of electro-magnetic forces.

In the sense of particles touchning particles, you never actually touch the kitty-kat. What we interpret as physical contact is, in reality, something much different than our perception.

Of course, all this comes from a guy who hasn't studied physics in that detail in a while - so I could be wrong.

Jamie

Ought Naught

Sorry that I wasn't more clear, Veil. What I mean when I say "mechanoreceptor" is just a special type of neuron that converts mechanical interactions into electrical signals that are conducted to the brain. In a lot of ways these receptors are like very small buttons that work like the keys on your keyboard. When you touch a ridged surface, for example, each of the ridges depresses rows of these 'little buttons' on your fingertip. The electrical signals from the depressed receptors are carried to the brain and "decoded" into the proper tactile sensation. Oh, and if you were wondering, "proprioceptors" are neurons that inform your brain of the angles of flexion/extension that your joints are at. This tells us things like whether our fingers are straight or bent, for example, without us having to actually look at them. This is also how we are able to touch our nose with our fingertips with eyes closed during a field sobriety test. I'm finding it hard to give you a concrete answer to your question about the plausibility of a long-range sense of "touch", and I think that my hesitation arises because there's is a little bit of 'slop' in the definition of the word. Maybe an example will help to get at your question. IIRC, there are examples where light sensing grids have been attached to skin of blind volunteers. These grids basically consist of little electronic transducers that emit a small electric shock (so mild as to not be uncomfortable) to the underlying skin when they receive a certain amount of light. Because there is a whole grid of these things, turning the grid towards an illuminated number 1, for example, will result in a pattern of little shocks being applied to the skin in the shape of a vertical bar (the number 1). After some time of wearing these implants, the brains of the volunteers began to actually interpret these patterns of small shocks as visual information, and they would report visualizing the "touch" information that the implants passed along to them. In a sense, these people were "touching" light, but that is only because the implants were converting light information into another form (electric shocks) that the skin was able to use and pass along to the brain for interpretation. So, are they "seeing" the light or are they "feeling" the light? I'm inclined to say that it is a little bit of both, but the fact that they reported visualizing the light information makes me lean a bit towards "seeing."

tronvillain

Veil of Fire:
Well, it would require a different sensory apparatus to obtain the necessary information, but there is no reason that it could not be processed to produce a sensation analagous to the human sensation of touch. Vision or sonar could provide at least some of the necessary information.

It would be plausible for such an alien to "see" shapes (and textures and temperatures) through touch, but not reflective properties such as colour. The details depend on it's actual sensory apparatus and processing. Does it continue to "see" objects after it is no longer touching them, or can it only remember touching them? How complex is it's sensory apparatus? A few limbs and digits, tentacles, cilia, hairs, membranes... the possibilities are endless.

echidna

I think you’d still have to use the inverted commas to describe such “feeling”. Truth is there is no English verb for what you are describing. Even sonaring would not clearly enough describe the action to the reader.

Ah hah, that opens things up a little. But isn’t that just a reverse metaphor for vision impaired people who “see” with their hands ?

echidna

Interestingly I recall that there is quite a difference in tactile imaging as performed by someone permanently blind as compared with someone who has lost their vision.

Someone once familiar with sight is able to translate a tactile sensation into a visual image, however someone never knowing sight purely creates a tactile memory.

Maybe someone else can expand on this …

PS, I’d suggest that if the beastie had auto-phosphorescent pressure-sensitive light sensors, even colours could be detected by touch. Certainly this would seem simpler than going to all the trouble of creating an eye.

Evolution would tend to improve the range of the light sensors though, but maybe that’s a bit too controversial.

It certainly generates a bizarre & creepy crawly kind of world anyway.

Veil of Fire

Well the critter is shaping up to be a semi-intelligent, land-dwelling thing that looks a bit like a big ball of tentacles/cilli, which sort of crawls along the ground. About as big as a large dog.

The tenatacles would be light-receptors, thus it gets a visual image of things by touching them, but I wanted its primary long-range sense to actually BE feel, but since I had no idea what the sense of feel was actually detecting, I had no idea if it was even mildly plausible to have a critter with an organ that can detect tactile sensations at a distance.

tronvillain

Well, the tentacles could just use pressure receptors to obtain the information for a visual image, but if colour is important you could add photoreceptors of some kind. It could improve the resolution of its vision simply by increasing the density of cilia, though if you wanted to retain active perception of colour while doing so each would require a light source.

daemon

This doesn't make a lot of sense to me. If there are photo-receptors in the tentacles, there's no reason it would have to touch to see; in fact, touching would occlude the light source unless what it was touching was, itself, the lightsource. Thus you'd have a set of photoreceptors that would, in most situations, be completely useless.

tronvillain

Ah, but it would have to touch to see, or at least to obtain any detailed visual information. At a distance it would probably only be able to detect large colour trends ("that direction is reddish), but if it touched an object with many cilia touch could provide the detailed shape information while the photoreceptors provided the colour.

tronvillain

Perhaps the lifeform is subject to frequent predation, but often survives and is capable of regenerating cilia. In that case, specialized sensory organs like eyes might not develop, redundancy being favoured instead. Alternatively, perhaps the lifeform lives in an environment where visibility is extremely limited and photoreceptors have to be extremely close, making concentrating them in one organ inefficient.