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.