Motion Bank: Two

Re-imagining Choreographic Ideas

Posts from the “Contributing Authors” Category

Risky Weight in Bebe Miller’s work

Posted on July 12th, 2013

One of the ongoing interests in our project is Bebe Miller Company’s use of what they call Risky Weight. In developing our terminology, Norah and graduate research assistant Malory Spicer have been compiling descriptions of Risky Weight from the dancers, Bebe, Talvin Wilks the dramaturge, and our consulting Laban Movement Analyst Melanie Bales. When reading these descriptions I was drawn to this definition of Risky Weight: the whole weight is a little more at risk and less linear and sequential to the body.


As we were working on this concept, Norah asked me about the possibility of tracking center of gravity in motion capture data and adding this information to our understanding of Risky Weight, a concept that has to do both with the viewer’s perception and the dancer’s use of his or her weight and gravity. To open this description further I assumed that this means creating situations when a performer’s body gets close to losing its balance, subsequently gaining stability.


In researching center (and line) of gravity and base of support in relationship to risky weight I discovered several perspectives on the estimation and perception of body balance. The precise biomechanics based estimation requires knowing the body weight and considering percentage of that weight associated with particular part of a body (see calculations detail in this ASU Biomechanics explanation).  The visual perception perspective, based on the qualitative approach to this problem in animation is reflected in the collection of tutorials at the Animation Physics website.  It demonstrates that a less precise approach to estimating center of gravity is still valid as long as the main principle is followed:

The body is off balance when the Center of Gravity (CG) is outside the Base of Support (BS). Thus the most stable position is when the two overlap (ie the person is laying flat on the floor), the next best thing is when the CG is directly above the BS.


Since Motionbuilder (our motion capture processing software) provides a basic operator which can estimate the CG (not as precise as biomechanics approach, but perhaps close enough), I used it to visualize the relationship of Center of Gravity, Line of Gravity (vertical line passing through the CG into the ground) and Base of Support. This exploration in Bebe’s work seems useful since the risk the performer takes is that of falling, which happens when their body is off balance.


In order to establish the BS I connected each foot’s ball and heel joints of the mocap skeleton into a rectangle stretched between the two feet.  The BS is reduced to a triangle when one of the joints is off the ground and to the area of one foot when the other foot is lifted. My threshold for when the foot is considered to be off the ground is set to 20cm to avoid excessive flickering caused by frequent shape change for the base of support, this can certainly be adjusted for higher precision if necessary.


This quick study may reveal that the qualitatively observed risky weight aspect of Darrell’s performance probably does not come from the state of physical imbalance. The occurrences and durations of this state are not that significant. Again, I am inclined to hypothesize that the viewer’s anticipation of the body becoming off balance is what creates the impression of Risky Weight but there is more to be explored here.


– Vita Berezina-Blackburn, Animation Specialist/ACCAD

Momentum in Bebe Miller’s work

Posted on July 8th, 2013

In examining the motion capture work from our January residency with Bebe Miller Company we are becoming interested in the possibility of tracing the momentum transfer through the body. The paths of momentum transfer reveal patterns of movement sequencing in the body. In both Darrell’s and Angie’s performances it is evident that several motions often happen concurrently. Performative tendencies that focus on simultaneity and dis-coordination of body segment motions are likely to interrupt viewer’s ability to anticipate movement and thus create fresh and surprising performance qualities.


There are a number of ways to approach visual representation of movement sequencing, and I thought it might be interesting to see this by making visible the sequences of joint rotations.  To set up this visualization I hypothesized that the initiating joint would rotate first, sending the waves of sequential rotations to the other parts of the body.  In the video of Darrell’s performance it is easy to notice many instances when sequences of joint rotations are initiated simultaneously or with minor offsets in time . I have used color coding to present two types of joint movement analysis.  The red figure indicates angular/rotation speed of joints (A) (the brighter the red the higher the speed), the green figure indicates linear speed of joints’ locomotion (L). As opposed to joint rotation speed, visualization of the linear (joint translation through space) shows a more even speed value distribution that is more sequential.


Since these may be a bit hard to notice at high playback speed of the captured motion this movie is at 1/4th speed.


While working on ideas about momentum I ran across a video on momentum transfer in parkour.   In this video, the second jump comes as a surprise. In order to get additional momentum to make the second jump possible, the landing position after the first jump had to be exaggerated… At a quick glance the shape of the body at the time of the first landing seemed to be that of trying to slow down.  By exaggerating this pose through leaning back and further lifting the arms backwards, it is possible to gain additional momentum. This hidden quality of getting the additional momentum is very intriguing as it also serves as a way of hiding anticipation of subsequent action. This triggers parallels between the animation concepts of motion anticipation and exaggeration and Bebe Miller’s ideas of “interrupting the inevitable” as well as “furthering”.


– Vita Berezina-Blackburn, Animation Specialist/ACCAD


Posted on June 17th, 2013

The Careful Scientist exercise requires following a small set of joint movement rules which dictate the ways a performer’s arms may move.  As part of the rule set no movement that is happening on the one side of the body can happen at the same time on the other side of the body.  Because the options are so discrete and constrained, the number of possible action sequences can be calculated.   As we have discussed here previously, the movements are limited to: Upper Arm Pointing Shoulder Rotation Elbow Flexion Forearm Rotation With a new action being chosen roughly every 1-3 seconds, there are millions of possible sequences for the first half minute of the exercise. Calculating the number of permutations was useful for giving a…

Dancer Awareness

Posted on July 16th, 2012

In response to our post Broader Notions of Two, Amsterdam-based dancer and researcher Bertha Bermudez wrote this very thoughtful reply:   “I keep thinking on what you wrote about two-ness in relation to time, space, social relations and the first main word I keeep thinking of is awareness. The act of reflection that is implied when dancing is, for me, the trigger of many of the forms of two-ness you are describing. When executing an action we are constantly busy with the path of it, or its evolution. Such a state needs of our attention to be placed on past events while executing new ones. Our present is a constant relationship between past experiences and their outcomes: potentials. We are then always split into…