Senses and Sensors

"If you had to choose, would you rather be deaf or blind?"  This was a fairly common question that kids asked each other when I was growing up.  I think my answer was "deaf", and I think it still is today.

When we have all of our senses, we often take them for granted, forgetting that there would be absolutely no way to perceive reality without them.  The least important senses in the modern world are probably a tie between smell and taste.  Although, I can imagine a time when these were necessary to correctly judge whether or not something was safe to eat.

I would argue that the single most important sense, however, is touch.  This one is probably taken for granted more than the others, and it actually encompasses so much of our interaction with the world.  Unlike the other four senses, which are local, this sense is global.  We have countless receptors all over our body sending information to our brain.  In particular, these receptors measure temperature and pressure: two critical inputs to safely navigate life.

In truth, sense of touch is not really an appropriate term.  We never actually touch anything.  inter-molecular lattice of which our skin is composed actually becomes more compact, and resists this departure from the equilibrium that preceded it.  It is for this reason that a "push force" is actually an electromagnetic force.  When we press our fingertips against something we cannot see, we judge it to be soft or firm based not on what it does, but rather what it does to us.  A given force per unit area at the contact causes our fingertips to deform slightly (to strain), and our internal pressure sensors inform us about what we are "touching".  When we "touch" other things, weak bonds also form between the atoms on our fingertips and those on the surfaces they are in contact with.  This can actually allow us to pull things too via static friction.

Some of our pressure sensors are more sensitive than others.  Those on our face are far more sensitive than those on our back, and their resolution is much better too.  This means that if there are two contact points near one another on our face, we can correctly assert that there are two, while on our back, we can be easily fooled, and think there is only one.

These kinds of observations are critical if one is to construct an autonomous robot.  Autonomous means that the control loops that link outputs to inputs are closed, and there is no need to input things manually.  When we think of our senses in this context, we realize that little distinguishes us from autonomous robots.  This line will certainly blur ever further as the twenty-first century progresses.  Are robots synthetic humans or are humans organic robots?  This is a modern day philosophical question.

Like a person, a functional robot must have sensors (gauges instead of receptors) and the ability to react to them (motors instead of muscles) in order to achieve a desired output.

If we were to try to build a robot with identical sensors to humans, we would have the easiest time with hearing and sight.  However, correctly judging what these moving images and oscillating air pressures represent would be very challenging.  "Machine vision" is widely used today in traffic monitoring and video security, while language interpretation has really taken off as well in recent years (consider IBM's Watson).

Scent and taste sensors are more difficult to create.  Monitoring these requires some form of indicator via chemical reaction.  A human's sensation of these are very refined: we can clearly differentiate between the smells of different substances whose chemical compositions are almost identical (as far as sensitivity goes, dogs have us beat hands down).

The biggest challenge to build our human-like robot, in terms of practicality, would be implementing an infrastructure of pressure and temperature sensors.  While such devices are decades old, the shear number required is daunting.

Once all of the inputs (sensors) are installed, the robot would need motors to carry out actions, and an extremely complex code to link the inputs and outputs.  It seems that the nature of this code is what truly distinguishes organic and synthetic beings.  But, with the progression of artificial intelligence, this gap may close before long.  And, my senses tell me that mankind is not ready for such a reality.