What is “natural” speech? Comparing free narratives and Frog stories in Indonesia

While there is overall consensus that narratives obtained by means of visual stimuli
contain less natural language than free narratives, it has been less clear how
the naturalness of a narrative can be measured in a crosslinguistically meaningful
way. Here this question is addressed by studying the differences between free
narratives and narratives elicited using the Frog story in two languages of eastern
Indonesia, Alorese (Austronesian) and Teiwa (Papuan). Both these languages are
not commonly written, and belong to families that are typologically distinct. We
compare eight speakers telling free narratives and Frog stories, investigating the
lexical density (noun-pronoun ratio, noun-clause ratio, noun-verb ratio), narrative
style (the use of direct speech reports and tail-head linkage), as well as speech
rate. We find significant differences between free and prompted narratives along
these three dimensions, and suggest that they can be used to measure the naturalness
of speech in oral narratives more generally.