All the details are in the paper from the US Naval Research Lab that you may read he

http://www.dtic.mil/get-tr-doc/pdf?AD=ADA614555 (Downloads a PDF)

Thanks Dave!
Reading this is fascinating. Here is a quote:
"Main (control)loop rates faster than 4 Hz were
tested (up to 10 Hz), but did not appear to have a positive effect on the success of the thermal centering.
Slower rates down to 1 Hz were tested, but appeared to consistently fly through lift and have poor centering ability. The rate of 4 Hz appeared to be a good balance between computational usage and thermalling performance."

Wow, does this apply to human pilots too? If so then you have to make a decision of to turn or not and which way to turn in less than one second or you might be missing lift. Somehow this does not sound right, especially because this small scale glider is flying slower than a sailplane.