Contrast and Perceptual Distinctiveness

Most ‘phonetically-driven’ or functionalist theories of phonology propose that two of the fundamental forces shaping phonology are the need to minimize effort on the part of the speaker and the need to minimize the likelihood of confusion on the part of the listener. The goal of this paper is to explore the perceptual side of this story, investigating the general character of the constraints imposed on phonology by the need to minimize confusion. The need to avoid confusion is hypothesized to derive from the communicative function of language. Successful communication depends on listeners being able to recover what a speaker is saying. Therefore it is important to avoid perceptually confusable realizations of distinct categories; in particular distinct words should not be perceptually confusable. The phonology of a language regulates the differences that can minimally distinguish words, so one of the desiderata for a phonology is that it should not allow these minimal differences, or contrasts, to be too subtle perceptually. In Optimality Theoretic terms, this means that there are constraints favoring less confusable contrasts over more confusable contrasts. There is nothing new about the broad outlines of this theory (cf. Lindblom 1986, 1990, Martinet 1955, Zipf 1949, among others), but it has important implications for the nature of phonology. First, it gives a central role to the auditory-perceptual properties of speech sounds since distinctiveness of contrasts is dependent on perceptual representation of speech sounds. This runs counter to the articulatory bias in phonological feature theory observed in Chomsky and Halle (1968) and its successors. Substantial evidence for the importance of perceptual considerations in phonology has already been accumulated (e.g. Boersma 1998, Flemming 1995, Jun this volume, Steriade 1995, 1997, Wright this volume; see also Hume and Johnson (2001) pp.1-2 and references cited there). This paper provides further evidence for this position, but the focus is on a second implication of the theory: the existence of constraints on contrasts. Constraints favoring distinct contrasts are constraints on the differences between forms rather than on the individual forms themselves. We will see that paradigmatic constraints of this kind have considerable implications for the architecture of phonology. The next section discusses why we should expect perceptual markedness to be a property of contrasts rather than individual sounds and previews evidence that this is in fact the case. Then constraints on contrast will be formalized within the context of a theory of phonological contrast. The remainder of the paper provides evidence for the key prediction of the theory: the markedness of a sound depends on the sounds that it contrasts with.