vendredi 10 juillet 2009

Phantom of the escalator

Very cool paper with the awesomest title ever given to a scientific report:

Fukui T, Kimura T, Kadota K, Shimojo S, Gomi H (2009) Odd Sensation Induced by Moving-Phantom which Triggers Subconscious Motor Program. PLoS ONE 4(6): e5782. (it's a free access journal)

Odd sensation? Induced by moving-phantom? Which moreover triggers subconscious motor program?? You got to be kidding me, that's a Nobel prize winner!

So let's check it out. The premise is extremely simple: have you ever stepped onto a stopped escalator? How did it feel? Yeah, I'm sure you know what I mean. I also have it. Well, that's what the authors of this paper set out to understand. They call it an "odd sensation". (One of the charms of the paper, I should mention, is that it is written in Japanglish).

Here's how the problem is stated in the introduction:
"When we encounter an escalator that is out of service, we recognize the escalator is certainly stopped and is not going to move; have the definite intention to step onto the stopped escalator (action to peculiar physical dimensions of stairs, see Fig. 1A), not a moving one (very familiar action); and then step onto it. After doing so, despite the proper awareness and intention, we frequently feel clumsy, as if our posture is awkward, our bodies heavier, and the steps are sometimes hard to climb. This clumsiness is associated with some kind of odd sensation." (emphasis added)
If you have no idea at all what these guys are talking about or what this "odd sensation" is supposed to be, then the paper will make no sense at all to you. It's really one of these things you have to experience firsthand to understand what it's all about. But still, even if you're like me and had this "odd sensation" dozens of times, you might ask why this is interesting at all. Well, the crucial point with this peculiar illusion resides in the interaction between top-down and bottom-up processes involved in visuo-motor integration. As the authors put it:
"...when we step onto a stopped escalator even with perfect knowledge that it is stationary, we are often surprised by the strange feeling accompanied by our own action. This feeling implies the involvement of subconscious processes against conscious awareness in the emergence of the odd sensation. Thus, this phenomenon raises an intriguing question as to how implicit motor programming escapes from conscious top-down control and offers an opportunity to study it."
In other words, it is definitely most interesting that such an effect should exist even when people know full well that the escalator is stopped. Why does it feel still feel so weird? What's going on, and how can we study this?

The authors decided to use an actual escalator to investigate this "escalator illusion". They set out three hypotheses that might explain it:
1) the effect is merely due to our unfamiliarity with stopped escalators. It coincides with specific body movements, of course, but the "odd sensation" only comes from "unfamiliarity" and that's it.
2) the effect is primarily due to the specifics of the escalator: it is true that an escalator's steps are deeper and higher than most normal stairs, and when it is stopped we have to accomplish nonuniform movements to climb it, which induce clumsiness (i.e. the first step taken is notably shorter than the following ones)
3) the effect emerges against our will, as our brain somehow triggers the motor program required to step onto a moving escalator even as it is perfectly evident that it is a stopped one. (in their words: "the subconscious emergence of the habitual escalator-specific motor program leads to the inappropriate motor behavior, which leads to the odd sensation".

To differentiate these 3 hypotheses (and it is clear that they favour the third one), they tested 3 conditions: subjects had to step onto either a moving escalator, a stopped escalator, or a wooden stair not looking like an escalator but having the same physical dimensions. There were only 7 subjects, and during all trials they wore movement trackers on their back and their heels. The kinematics of upper and lower body was the main measure studied, and after each trial they also were asked to rate on a 1 to 5 scale "the extent to which they felt some kind of odd sensation".

I will spare you an account of the detailed results of this study, which are quite elaborate. The analyses I must say are very original and smart, but I wonder how many journals have turned down this study before it was published in PLoS One. I have the feeling that many reviewers would have been put off by the overkill nature of all these kinematic data and path analysis statistics for the sole purpose of investigating an "odd sensation". Well, you ask me, this should be published in Science or Nature, no less.

The discussion is a little bit redundant, but it can be conveniently summarized as follows:
"the prerequisite for the emergence of the odd sensation is an inappropriate motor behavior against the current situation resulting from the habitual motor behavior for a moving escalator. People may not be able to suppress this behavior despite completely understanding the current stopped escalator situation.


The conflict between the motor intention and the sensory outcome would be the important factor for the emergence of some kind of strange/peculiar feeling."

Well, this is the trouble with habits. They only work insofar as the context doesn't change too much. But the authors cannot really explain where this "subconscious" motor program specialized for escalator climbing comes from in the first place. How many escalators do you have to use in a lifetime to acquire the "subconscious motor program" leading to this "odd sensation"? What is more, it is clear to me that the "sensation" is there as well when you have to climb down a stopped escalator, and when you walk on one of these very long airport treadmills that happen to be nonfunctional. Does the interpretation based on the kinematics of climbing up still hold? I would also like in the future to know more about exactly what the "odd sensation" is. In the introduction, they mention clumsiness, heaviness, and awkwardness. Are these all synonymous, or different dimensions of the sensation? Can these be dissociated, for instance if we modulate the speed of the escalator (very slow instead of stopped, and so forth)? Finally, I'd like to ask why the word "phantom" is used in the title, but not at all in the text? This is very bizarre and disappointing, as it appears also in the abstract:
"moving escalator-specific motor actions emerged after participants had stepped onto the stopped escalator despite their full awareness that it was stopped, as if the motor behavior was guided by a ‘‘phantom’’ of a moving escalator"
Well, as a self-proclaimed phantomologist, I can only say that I perfectly agree with the use of the word (although it is not clear if we're talking of a "phantom moving escalator" or "phantom self on a moving escalator"), but it really boggles the mind that the concept should be brought about in the title and the abstract, and then be entirely forgotten. Another case of vanishing phantoms, I guess.

Despite these very few caveats, I'd like to repeat that this is a very delightful paper. And I'd like now to share with you something it reminded me about. The authors have this to say in the introduction:
"when going up or down stairs, we sometimes extend the foot in expectation of an additional step at the end of the stairs, which causes us to stagger."
This they say is entirely different from the escalator illusion because in this case we realize that we made a mistake, "a self-prediction error caused by our thinking there was an additional step", whereas in the escalator case there is no error, we know and see that it is stopped. Well, this brought to my mind a very peculiar account from a very peculiar book. It allows me to demonstrate that the use of the word "phantom" by the authors of the escalator study was perfectly appropriate, as there could be a nice continuity from the "odd sensation" they talked about, to the situation where we lose our footing while climbing down the stairs as we expect an additional step that is not there, and then onto the full-blown "phantom" projection, meaning disembodiment as in out-of-body experiences. This is in my opinion all part if phantomology.

The demonstration is found in the account by a man named Sylvan Muldoon of his repeated out-of-body experiences (see Blackmore's account of this interesting fellow). In his main book, The Projection of the Astral Body, Muldoon explains in some excruciating details the many ways and situations to induce an "astral projection". Of particular interest here is a subsection of chapter 2 that explains how an OBE can be induced by mistakenly expecting an additional staircase step.
A projection caused by a mis-step
Here is an example of how an unexpected jar will throw the phantom out of coincidence. One night, a few years ago, I was coming down the stairs of my home. I had been sleeping, and was still quite drowsy. There were fifteen steps, and I had trodden up and down them hundreds of times, having lived in the house all my life. Just why I do not know, but, as I reached the bottom step, I tried to take one step more (many of us have done this), and the impetus jarred me vigorously.
A breath-taking sensation shot through the pit of my stomach, and even before the physical dropped to the floor, I found myself projected from it, in a perfectly conscious state. (...) I both
saw the physical mechanism fall to the floor and also felt it fall, while standing several feet from it. Let me analyse this, and see what actually happenened, for by doing so we shall discover the fundamental law of astral projection.
It must be understood that it is not the conscious mind which causes projection, but it is the subconscious Will.
The Projection of the Astral Body, Chap. 2, p.64)
There goes some "odd sensation", isn't it? Note how he calls the OBE a "phantom thrown out of coincidence", which is actually a wonderful and accurate way to put it from a cognitive perspective I think. Note also how Muldoon uses almost exactly the same terminology than the Japanese authors of the escalator study, positing a conflict between the "subconscious will" (the "motor programs") and the physical outcome of the event. In modern words, we would say that the body schema and the body image are not coinciding, hence the induction of an "odd sensation", which could perhaps manifest itself in more extreme situations (and possibly quite rare individuals) as an OBE.

Ok, I refrain to talk here about similar effects found in elevators. Remind me to discuss someday the wonderful paper by Schilder on the topic (
Parker, S. & Schilder, P. (1930). Das Körperschema im Lift. Zeitschrift für die gesamte Neurologie und Psychiatrie, 128: 777-783).

Also, if he agrees to let me do so, I might also discuss in the future a nice idea for a project that my colleague Pär Halje proposed in less than 5 minutes when he was pressed to come up with something for a PhD class. He called it "The trampoline after-effect", and I think the idea is just too wonderful to be left alone. More phantomology induced by cool artifacts.

And one last word about escalators: French readers might want to learn more about
the international plot of escalator repairmen. We know what you are doing, bastards, so stop it already.

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