I'm assuming this is a follow up for
In the future, you may want to consider updating that question so all information are captured in one place.
The syntax you mentioned above is a new way to invoke the object that is introduced in R2016b. If you are in 2013a, try
[sensorpos,sensorvel] = step(sensormotion,1/prf);
and see if solves the problem.
HTH
