Showing posts tagged biomechanics

Dunlap, K. and Mowrer, O. H. (1930). Head movements and eye functions of birds. J. Comp. Psychol. 11, 99–113.

People make a lot of hay out of the series of photographs by Eadweard Muybridge that Governor Leland Stanford commissioned to figure out whether all four hooves of a galloping horse are airborne at the same time. Muybridge ingeniously used an array of cameras that were triggered sequentially by the horse busting through a series of trip wires. The result of this experiment was that there was definitely a moment in the horse’s gait when all four feet were off the ground. (Stanford went on to found the university that produced Olympic water polo player Tony Azevedo; Muybridge ended up shooting a man who slept with his wife, but was acquitted on grounds of “justifiable homicide”.)

Now I don’t want to dump on the birth of cinema, but I’ve just been out watching horses gallop around all morning, and I’m pretty sure that I could reproduce Muybridge’s experiment with some study drugs and a mug of properly mulled cider. Things are always clearer in hindsight, but it didn’t take much squinting to convince me that horses are airborne every quarter second or so. Perhaps Muybridge and Stanford were half blind from living in an era before proper sunglasses, or maybe horses were faster in the 19th century because there were no clocks and all the conductors had to count continuous Mississippis to keep the trains on time.

Whether or not the Muybridge horse study was necessary, subsequent developments in rapid picture-taking have proven incredibly useful for the study of biomechanics. Today I want to discuss an early example of how the camera can be used to compensate for the inability of us humans to fully appreciate animals. 

Many people have wondered, “What’s up with pigeons bobbing their heads all crazy while they walk”, but most people are too afraid to blog about it. As Dunlap and Mowrer, the authors of today’s sick pape, put it, “The forward and apparent backward movements of the head which pigeons, chickens, and certain other fowls display while walking have been commented on by various persons orally, but seldom in print.” 

It may have occurred to you that this jerky head movement is an accident of the pigeons walking gait, perhaps analogous to the swinging of a human’s arms. But this is wrong. In 1930, Dunlap and Mowrer took some great photos that proved that bird head bobbing is just an illusion. In fact, it is you, the viewer, who is lurching ferociously back and forth, and the bird is perfectly motionless! That’s not actually true. What is really happening, Dunlap and Mowrer found, is that when the bird’s body is moving, the head is completely still. In other words, the head is locked in position relative to the forward moving body. Then, when the body stops for a brief moment, the head thrusts rapidly forward to a new position. So, overall, the head is maintained in a stable position relative to the body. The stroboscopic photo above, from a sick follow-up pape by B.J. Frost in 1978, illustrates this nicely.

This head stabilization has obvious benefits for vision, as it is much more difficult to analyze a visual scene when your head is shaking. Another set of experiments by B.J. Frost in the 70’s clearly demonstrated that head-bobbing is controlled by vision, as pigeons walking on treadmills don’t bob at all (because the visual scene is stationary).

The findings of Dunlap and Mowrey in 1930, and subsequent work by B.J. Frost and other enthusiastic bird bio-mechanics, are a superb example of how the world is incredibly fast and confusing, and only photographic magic and detailed quantification can distill truth from all the chaos.

Contributed by butthill

Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes.
King HM, Shubin NH, Coates MI, Hale ME.
Proc Natl Acad Sci U S A
. 2011 Dec 12.

This week, Sick Papes brings you an exclusive interview with Dr. Heather M. King, the celebrity author of a dangerously feverish pape that rejiggers how we think about the the evolution of tetrapod locomotion (i.e., how four-legged animals walk).

SP: Your pape describes a hybrid walking/swimming gait in lungfish which looks curiously like that of four-legged critters that walk on land. Do lungfish need to trundle along on the bottom of the lake, or can they also swim throughout the water column like normal self-respecting fish? What do you think is the advantage of the lungfish style?

HK: They certainly can use their body/tail to swim as typical fish do, but they tend to do this only when frightened or startled.  However, they seem to nearly always use their fins for walking instead.  We don’t know why exactly they do this, but we have some hypotheses: using the fins to walk instead of the whole body would use less energy, since the muscles in the fins are so much smaller than the muscles in the body.  Lungfish live a long time and don’t seem to move much (in my experience) so their metabolism might be lower than that of other fish, and it would likely be to their advantage to use the fins for slow movements.  In addition, aquatic animals can sense each other by tracking the vibrations in the water made by other animals, and it’s possible that lungfish use these smaller movements to be more ‘quiet’ underwater, which would help them both avoid predators and ambush potential prey. 

SP:  Lungfish defy classification: they possess traits of both fish and land-dwelling critters. Some describe them as unlikely monsters. Do you identify personally with these misfits of the animal kingdom? If so, what childhood experience led you to realize that you were somehow “different”?

I knew I was different the first time I saw the lungfish.  It was like looking in a mirror.

SP: I read on Wikipedia that lungfish can survive the seasonal drying out of lakes by just chilling in the mud for many months. Is it possible that the walking-like propulsion you described is also useful during mud season?

HK: Yes, that’s true. They make a cocoon of mud and their own mucus and survive in a state of hibernation for up to 4 years.  This behavior has been studied fairly well, and it turns out that they actually use their axial muscle and head to burrow into the mud.  The fins are not strong or large enough to contribute.

SP: Imagine that you had a time machine and high-speed video camera. Given your obsession with the “water-to-land transition”, what historical epoch would you travel to, and what would you film? Who would you bring with you as your ideal assistant?

HK: I would like to travel to the Mid or Late Devonian with my camera, and film any creature I saw.  I would probably take my husband as my assistant because he’s the only one that would still help me/like me as I traversed the near-alien landscape in search of large fishapods, all while muttering about the insane amounts of Nature papes I would author upon returning to the present day.  I can be a little obnoxious sometimes.

SP: Figure 3 clearly shows a lungfish doing a push-up, yet your paper describes this behavior as “lifting the body and appendages clear of the substrate”. Is there some reason that you chose to use this jargony description instead of the more familiar colloquialism? Isn’t this what’s wrong with science, that scientists refuse to describe anything in plain-spoken English that my dad, Newt Gingrich, or your average hairdresser could understand? Why not just call the pape: “Lungfish walk like horses and do push-ups”?

HK: I didn’t realize that you were the son of Newt - tell him to rein it in a bit on TV or he’s gonna blow this nomination thing.  You will have to take this one up with the powers that be - such jargon is necessary for publication, since so many journals demand short, succinct, articles.  Taking the time to explain exactly how I define ‘walk like horses’ and ‘push-ups’ would have taken at least half a page.  Plus, I doubt your dad, Newt Gingrich, and I have the same idea of what ‘walking like a horse’ means.

SP: You show that lungfish not only walk- they also bound. Do they move faster when they bound, like cats?

HK: Based on studies on other animals, gait transitions are indeed associated with changes in speed.  However, we did not find evidence for transitions to the bounding gait being associated with an increased speed.  Perhaps the lungfish know that they are outsiders, and like many outsiders, decide not to conform to the norm.

SP: Your pape is being covered extensively by the press (National Geographic, Discover, Scientific American, NY Times). Why do you think your pape has received so much attention compared to other PNAS papes from 2011, like, for example, that one about flies perceiving a really fascinating visual illusion?

HK: I am sure that said fly vision pape is of equal or greater value than my pape - all I can say is that some of my co-authors are very good at promoting their research and know the value of a well-written press release.  I merely benefit from their experience and notoriety.  

SP: My sources report that you were once so exhausted from working on this project that you fainted in a bank, throwing thousands of dollars of cash into the air as you collapsed to the floor. Any comment?

HK: Science is fucking hard.

Contributed by butthill
hit counters
hit counter