Lifiting a cup to the mouth

Dagmar Sternad could compete for most passionate researcher on campus and land a seat near the top. Her stern gaze and flaming red hair only add to her intensity.

Sternad is a professor of biology, electrical and computer engineering and physics, but as she says, “don’t even try to label me.” Her work, which focuses on the “control of human movements” bridges the gap between a variety of disciplines, from biology to bioengineering, from physics to physical therapy.

“We want to understand how humans generate functional behavior such as grasping a cup and leading it to the mouth,” she says — lifting a teacup off the desk in front of her. “How does the brain direct my hand to a visually perceived target and then apply the right amount of forces such that the cup can be lifted? What kind of sensory information tells the hand to hold the cup such that it doesn’t tilt?”

These are the types of questions Sternad and her team explore using a variety of experimental and theoretical approaches in the “Action Lab,” where I visited her a few weeks ago. I found myself attempting to direct a virtual cup into a virtual box without dropping the virtual ball it contained. I grasped the handle of a robotic instrument and pushed it through the air, watching a cartoon model of the cup move across a screen in front of me. Just as you may feel the force of a sloshing liquid inside a cup as you race across the room to answer the phone hoping not to spill, I felt a force from the instrument in my hand — an effect programed into the computer model to mimic real life scenarios.

My first try was pretty poor, I dropped the ball and overshot the box. But I soon learned how to control my movements to achieve better results, which is exactly what Sternad and her team are interested in. They look both at healthy and impaired populations and have found that we all keep a safety margin within which we operate, which is a function of our variability. If you have tremors in your hands, for example, bringing a coffee cup to your mouth would require a larger safety margin than your neighbor.

The team was surprised to find that this was true even for children with dystonia — a neurological disorder that causes high levels of variability in their movements. Given the children’s seemingly random uncontrolled movements, they expected this population to be unable to control their safety margin.

“Humans are aware of their variability and adapt their movement strategies accordingly,” says Sternad.
While she is particularly interested in the very basic science behind “lifting a cup to the mouth,” her work could inform the development of new therapies for physically impaired individuals.

Photo by Mary Knox Merrill.