This question/idea has been going around in my head for a while now. It might be an "ask a neurologist" question.

It's clear that our motor control and sense of sight need to be tightly coupled. Our brains need to understand relative motion, when both ourselves and a distant object are moving relative to the static earth/background.

I assume we evolved in a world where we only moved under our own power (i.e. relative motion only occurred when we moved our body).

So, now we live in a world where we frequently experience relative motion without using our bodies to directly impart power (cars, buses, trains) etc. Also, in order to control these vehicles we need to move our bodies in a very different way to the motion that we would normally use to move.
In the case of pedal bikes, we directly impart power to make us move, but in a different way than we would if running or walking.

I find it fascinating that the brain doesn't get very confused by the eyes telling it "you're moving" and motor control saying "you're sitting still in a chair on a bus" (for example). And yet when it comes to complex motion such as walking, running, shooting, climbing, the two systems can interact seamlessly.

My question is: is this ability to selectively couple/decouple our senses to/from our own actions a necessary result of the evolution of our brains? Or could an accident of evolution have meant that any motion we experience that doesn't come from our body moving is so alien to our minds that we just can't cope with it?

Are there any organisms that cannot cope with this kind of motion?

I may not have explained myself very well.

Thanks for reading anyway,

James F

I'm not sure it's so clear cut.  Perhaps this is why learning to ride a bike is not trivial, or why people get car/bus/motion sickness.

Perhaps we just habituate to these situations.

I'd be interested in what others have to say.

I agree and more broadly this will apply to many aniamls e.g. sitting on a moving object (branch or log in water) and yet fixating on an object close by or far away. This is a lovely example of how adaptive evolution has allowed the brain to interpret multiple context-dependent inputs that in turn allows specific outputs that are not directly related to the "raw" visual input data.

It is indeed a good question, and one into which a lot of thought has been put, certainly by cognitive scientists if not by (neurologists!).

Like Peter says, the answer is not simple and draws on insights from numerous disciplines, neuroscience, psychology, even physics (esp. wrt inertial frames). Unfortunately it would take far to long to go through all of these and it is beyond the remit of the site.

Although I'm not an evolutionary biologist, I am going to assume you are broadly right about the idea we evolved in an environment where, like you say, our movement was closely linked to our own locomotion.

I think the first thing to say is that it is probably not about 'decoupling' but more about integration. Our minds are constantly trying to make sense of the world and draw on all kinds of inputs from different sources in order to build up a picture of what is going on. The sensory inputs from the brain contribute to our perception of this. Sometimes it gets it rights but other times it gets it wrong. Playing these 'games' with our minds is one of the ways in which psychologists gain greater insight into the workings of the mind. The work of Escher (the artist famous for his drawing of impossible figures):


and a multitude of experiments, e.g. the Ames Room:

http://psylux.psych.tu-dresden.de/i1/ka … _room.html

and many others (this site includes illusions of motion):


have greatly enhanced our understanding of perception and the workings of the mind. In some cases failure of participants to interpret these illusions has been enough to reject hypotheses of the way in which perception works. In many of these cases, even knowing that the illusion is an illusion, and how it works, we still cannot help but see what we see, knowing that it can't be right or is impossible.

Moving to the kinds of phenomena you are talking about, I would suggest there are more cases where the brain does get confused than is immediately obvious. To take your own example of sitting in a chair while a vehicle is moving, actually, this is a common experience and it does confuse the brain. If you are sitting on a train and setting off from the platform, or another train next to you is moving, it is a common experience that we are unable to tell whether it is us that is moving, or the platform is moving - even though the idea that the platform is moving is perverse and we know that can't be happening.
But things aren't all bad! In many cases we DO understand what is going on, and I would agree with the commentators above. The bike analogy is a good one, and it takes a long time for people to understand what is going on when their bodies are in motion without their bodies doing the the motion. Again, there are a lot of studies looking into this, both from a developmental perspective (a child growing up) and from a comparative perspective (when other cultures are exposed to new technologies) and how they come to 'understand' what is happening. I imagine that motion sickness is a large part of that learning!
But this isn't the end of the story by far and it is a live issue even for adults in advanced societies. Astronauts go through extensive training in order to help them to get used to the experience of movement in space - it takes a lot of time and, if this article is anything to go by (based on a quick web search), not entirely something we have yet got a real grip on:

http://news.discovery.com/autos/motion- … -space.htm

I think this is probably a good example of where people are moving but not under their own propulsion, and still (in the main) people are able to learn (and to some extent cope with) this.

In terms of other animals, I don't know. I picture a polar bear floating down a stream on a glacier, a fish being swept downstream by currents, a bird gliding (perhaps Peter can give an insight into animal perception). These may be trivial examples, but during these brief periods where locomotion is 'decoupled' (to use your notion) from other movement, are birds/fish thrown into a state of confusion before they start to manually propel themselves again? If not, is this because it is an experience they get used to with memory they were moving covering the gap?