Each year, the annual Dynamic Walking Conference continues to be one of my favorite conferences. An incredible mix of smart and creative people. Here I am rambling on about closing the loop on sensorimotor systems. 
Congratulations to Robert Nickl, who defended his thesis today. Robert’s thesis, entitled “Spatial and Timing Regulation of Upper-Limb Movements in Rhythmic Tasks,” uses a virtual juggling paradigm to investigate multisensory control during rhythmic arm movements.
On October 16, 2017 LIMBS lab member Amanda Edwards defended her PhD dissertation entitled “Feedback Control in the Cerebellum”. Amanda was jointly co-advised by Dr. Amy Bastian.
Here is Amanda discussing the merits of chasing little red dots as a means by which to get a PhD.
CONGRATS AMANDA!
In a recent talk at the CMU Robotics Institute, I decided to give a quick impromptu demonstration of what it means to “stabilize an unstable system,” thereby making it easier to apply system identification. This was in relation to my presentation of my previous PhD student Manu Madhav’s paper:
M. S. Madhav, S. A. Stamper, E. S. Fortune, and N. J. Cowan. “Closed-loop stabilization of the jamming avoidance response reveals its locally unstable and globally nonlinear dynamics”. J Exp Biol, 216:4272-4284, 2013.
Shahin Sefati, Alican Demir, and Mert Ankarali (left to right, Hopkins gold regalia) were hooded today by ME Professor Louis Whitcomb (Yale regalia). Sadly, I am out of town and didn’t get to do it myself, but was very happy that my colleague and academic brother stepped up and did the honors for me!
-Noah
As proof that the LIMBS lab has a friendly lab culture (maybe too friendly?), LIMBS members Alican Demir and Erin Sutton tied the knot on January 3, 2015. All joking aside, warm congratulations, Alican and Erin!
PhD Student Alican Demir presented his research at an IROS 2014 workshop on “Active Touch in Animals and Robots“.
Special thanks to our collaborators, Jean-Michel Mongeau and Bob Full.
From right-to-left Jusuk Lee (graduated 2009), Alican Demir (will graduate 2014), Vinutha Kallem (graduated 2008), and Vinutha’s husband Pranava. What a great reunion!
Here are Vinutha and Jusuk in front of a million dollar door in Chicago:
In engineering and mathematics, t is the quintessential independent variable: an immutable quantity in terms of which all other variables depend. Most control systems do require a clock, but clocks have been engineered with such low drift rates that for all practical purposes, imperfections in chronometry have been largely ignored.
Biological systems do not have it so easy. Biological clocks were not “engineered” on top of a physical phenomenon like the oscillation of a quartz crystal. Rather, biological wetware must keep time over many scales using physiological, neural, and biochemical mechanisms. Biological clocks are typically described as nonlinear dynamical systems exhibiting limit cycle behavior where the phase of the system advances monotonically with the passage of time. For example, circadian rhythms and other longer-term processes highlight the importance of external cues in the timekeeping process. Circadian and circannual rhythms, for example, are regulated by changes in daylength, temperature, and other environmental cues.
So, while uncertainty in time is justifiably neglected in the design and analysis of most engineering control systems, perfect timekeeping is a poor assumption for the modeling and analysis of biological control systems. Indeed, timekeeping during simple human motor control tasks involves errors of around 10% of the movement cycle duration. Despite this extremely high level of temporal imprecision, the overwhelming majority of computational models of the human motor control makes the implicit assumptions that time is known. Who knows what happens to any of these analyses when our assumption about perfect timekeeping is relaxed?
These three papers begin to address this question:
S. M. LaValle and M. B. Egerstedt, “On time: Clocks, chronometers, and open-loop control,” in Proc. IEEE Int. Conf. on Decision Control, 2007, pp. 1916–1922.
S. G. Carver, E. S. Fortune, and N. J. Cowan, “State-estimation and cooperative control with uncertain time,” in Proc. Amer. Control Conf., 2013, in press.
A. Lamperski and N. J. Cowan, “Time-changed linear quadratic regulators,” in Proc. Euro. Control Conf., 2013, in press.
Written by Noah J. Cowan with Eric S. Fortune, Andrew Lamperski and Sean G. Carver.
