Dissimilation - Causes

Causes

There are several hypotheses as to what causes dissimilation. John Ohala posits that listeners are confused by sounds that have long-distance acoustic effects. In the case of English /r/, rhoticization spreads across much of the word (that is, in rapid speech many of the vowels may sound like they have an R in them), and it may be difficult to tell whether a word has one source of rhoticity or two. When there are two, a listener might wrongly interpret one as an acoustic effect of the other, and so mentally filter it out.

This factoring out of coarticulatory effects has been experimentally replicated. For example, Greek pakhu- (παχυ-) "thick" derives from an earlier *phakhu-. When test subjects are asked to say the *phakhu- form in casual speech, the aspiration from both consonants pervades both syllables, making the vowels breathy. Listeners hear a single effect—breathy voiced vowels—and attribute it to one rather than both of the consonants, assuming the breathiness on the other syllable to be a long-distance coarticulatory effect, thus replicating the historical change in the Greek word.

If Ohala is correct, one might expect to find dissimilation in other languages with other sounds that frequently cause long-distance effects, such as nasalization and pharyngealization.