Subject: phonemes From: "Keith R. Kluender" <KLUENDER(at)MACC.WISC.EDU> Date: Wed, 1 Apr 1998 08:20:00 CSTNeil Todd's thoughtful contribution was informative. I only add a brief caveat to this discussion regarding the assumption of phonetic stages. It is sometimes useful to consider how speech perception would work if phonemes did not exist as an intervening stage between acoustic input and lexicon. Speech perception researchers, including myself, have perseverated on perception of phonemes as if they are the real entities to be explained. Much of this heritage arises from the utility of phonemes to efficiently describe distinctions between morphemes. As such, phonemes are an invention by linguists to describe language at a given level of detail. Phonemes may or may not exist as a separable level of analysis in the process of speech perception. It sometimes is useful to imagine a lexicon that is primary encoded in auditory dimensions. What is true is that, if one wishes to economically describe the variance in this lexical space (e.g., principle components), much or most of the variance in the space could be described in terms of dimensions that map fairly well on to phonetic distinctions. However, this simply recapitulates the linguists' descriptive claims. It does not necessarily afford phonemes any process role. Instead, phonemes may be an emergent property of a sufficiently well-populated lexical space. I have not scrutinized the literature Todd shares, so I'd like to maintain some caution before claiming that those findings can be reinterpretted without recourse to a phonetic stage of processing. I would be hopeful, however, that this is the case. By avoiding commitments to phonemes, I've found it easier to think about processes of perceptual development concerning perception of speech. Many studies (e.g., Werker, Kuhl) concerning changes in speech perception over the first year of life often are interpretted as evidence that infants "learn" the mapping of phonetic units specific to their language environment. The functional question is what is the cash value of phonemes to an infant. Does the infant learn phonetic categories (which have no communicative value in and of themselves) simply to be able to later recognize sequences of phonemes to understand words? I would argue that it may be more sensible to consider the infant to be developing an auditory lexicon based upon exposure to words, and that the apparent development of phonetic categories is really the typical result of perceptual learning whereby the system comes to efficient- ly encode variance and covariance in the environment. (Note: words do not exist as segmented entities in the input, and related statistical learning serves the purpose of parsing fluent connected speech into words, e.g., Saffran's data from 7-month-olds.) I realize that this has come a long way from concerns about how one separates speech from other environmental sounds. It is worth considering, however, that Dennis Klatt's LAFS (lexical access from spectra) model of speech recognition may turn out to be closer to reality than would be apparent from contributions by speech perception researchers such as myself. It may pay to not be sanguine that the goal of speech perception is to arrive at phonemes. -- Keith Keith R. Kluender Department of Psychology University of Wisconsin 1202 West Johnson Street Madison, Wisconsin 53706 608-262-9884 (office) 262-6110 (lab) 262-4029 (fax)