Empirical Translation Studies have recently extended the scope of
research to other forms of constrained and mediated communication,
including bilingual communication, editing, and intralingual
translation. Despite the diversity of factors accounted for so far, this
new strand of research is yet to take the leap into intermodal
comparisons. In this paper we look at Lexical Diversity (LD), which
under different guises, has been studied both within Translation Studies
(TS) and Second Language Acquisition (SLA). LD refers to the rate of
word repetition, and vocabulary size and depth, and previous research
indicates that translated and non-native language tends to be less
lexically diverse. There is, however, no study that would investigate
both varieties within a unified methodological framework. The study
reported here looks at LD in spoken and written modes of constrained and
non-constrained language. In a two-step analysis involving Exploratory
Factor Analysis and linear mixed-effects regression models we find
interpretations to be least lexically diverse and written
non-constrained texts to be most diverse. Speeches delivered impromptu
are less diverse than those read out loud and the non-constrained texts
are more sensitive to such delivery-related differences than the
constrained ones.