<P> Ben Zimmer discusses the use of the term "ON a steep learning curve" in an article "A Steep Learning Curve" for Downton Abbey, concentrating mainly on whether it is an anachronism . "Matthew Crawley, the presumptive heir of Downton Abbey and now the co-owner of the estate, says,' I've been on a steep learning curve since arriving at Downton .' By this he means that he's had a difficult time learning the ways of Downton . Unfortunately, people didn't start talking that way until the 1970s ." </P> <P> Zimmer also comments that the popular use of steep as difficult is a reversal of the technical meaning . He identifies the first use of steep learning curve as 1973, and the arduous interpretation as 1978 . </P>

Which of the following is a behavioral definition for learning