  Mental health counseling is an enterprise with profound societal importance
where conversations play a primary role. In order to acquire the conversational
skills needed to face a challenging range of situations, mental health
counselors must rely on training and on continued experience with actual
clients. However, in the absence of large scale longitudinal studies, the
nature and significance of this developmental process remain unclear. For
example, prior literature suggests that experience might not translate into
consequential changes in counselor behavior. This has led some to even argue
that counseling is a profession without expertise.
  In this work, we develop a computational framework to quantify the extent to
which individuals change their linguistic behavior with experience and to study
the nature of this evolution. We use our framework to conduct a large
longitudinal study of mental health counseling conversations, tracking over
3,400 counselors across their tenure. We reveal that overall, counselors do
indeed change their conversational behavior to become more diverse across
interactions, developing an individual voice that distinguishes them from other
counselors. Furthermore, a finer-grained investigation shows that the rate and
nature of this diversification vary across functionally different
conversational components.
