This talk will involve a discussion of two types of context-induced and naturally-occurring speech modifications or enhancements. One concerns localised hyperarticulation induced by prosodic boundaries in three Australian languages, and the other, the increased intelligibility of speech produced in noise (so-called Lombard speech) in American English. Both types have been associated with increases in articulatory effort or strength, which have spectral and durational consequences. The results of acoustic and perceptual analyses will be presented.