Annotating Speech Turn
Goals:  We seek to identify periods for each speaker when
  they have the floor, or are on turn, but that is not a well-defined
  condition, so some heuristics are in order.  I provide guide lines
  and specific examples below.
Usually, in a dyadic conversation, one person is speaking and the
  other listening.  However, real conversation is much messier than
  this.  There will be periods, sometimes protracted, in which two
  subjects vie for sole command of the floor, overlapping in their
  speech.  There may also be periods in which nobody in particular has
  the floor.  Thus we annotate Turn on a by-speaker basis, rather than
  by-pair, and we acknowledge that zero, one, or two people may have
  "Turn" at any given moment.
The best way to annotate turn is to listen attentively to the
  conversation.  This is best done in Praat, where it is possible to
  follow the time course of the speech with some precision.  Examples
  given here will be somewhat harder to follow, due to the separation
  of sound and annotation. 
First, consider the following extract: