Word Frequency and Context of Use in the Lexical Diffusion of Phonetically Conditioned Sound Change

Word Frequency and Context of Use in the Lexical Diffusion of Phonetically Conditioned Sound Change

Joan Bybee


Lexical diffusion refers to the way that a sound change affects the lexicon. If sound change is lexically abrupt, all the words of a language are affected by the sound change at the same rate. If a sound change is lexically gradual, individual words undergo the change at different rates or different times. (...) One early contribution to this debate by Schuchardt (1885) is the observation that high-frequency words are affected by sound change earlier and to a greater extent than low-frequency words. (...) phonetically conditioned changes that affect high-frequency words before low-frequency words are best accounted for in an exemplar model of phonological representation that allows for change to be both phonetically and lexically gradual. (...) a word’s contexts of use also affect the rate of change. Words that occur more often in the context for change, change more rapidly than those that occur less often in that context. (...) sound changes can also progress more rapidly in high-frequency morphemes. (...) the contexts of use determine the rate at which a word or morpheme undergoes a sound change.



1. Regular sound change or lexical diffusion?

The hypothesis that sound change is lexically regular seems well supported by the
facts of change. When we observe that two languages or dialects exhibit a phono-
logical difference, it is very likely that this difference is regular across all the words
that have the appropriate phonetic environment. This observation is fundamental to
the comparative method; the establishment of genetic relations and the reconstruc-
tion of protolanguages are based on the premise that sound change affects all words
equally. Schuchardt (1885) was one of the detractors from this position. When he
observed sound change in progress, he noted that all words did not change at the
same rate and that the differences were not due to “dialect mixture,” as was often
claimed by the Neogrammarians, who supported the regularity position.


Labov (1981, 1994) He proposed two types of sound change: “regular sound change” is gradual, phonetically motivated, without lexical or grammatical conditioning, and not influenced by social awareness, whereas “lexical diffusion” change, such as the phenomena studied by Wang, is “the result of the abrupt substitution of one phoneme for another in words that contain that phoneme” (Labov 1994:542). According to Labov, this type of change occurs most often “in the late stages of internal change that has been differentiated by lexical and grammatical conditioning” (ibid.). Labov went so far as to propose that certain changes, such as the deletion of glides and schwa, would be regular changes, while the deletion of obstruents would show lexical diffusion.


(...) even gradual, phonetically conditioned change exhibits gradual lexical diffusion (...)


Hooper (1976) identified a lexical diffusion paradox. Reductive sound change tends to affect high-frequency words before low-frequency words, but analogical leveling or regularization tends to affect low-frequency words before high-frequency words.


2. Frequency effects on regular sound change

Sound changes that are complete can be identified as regular or not, depending upon whether they affected all lexical items existing at the time of the change. Ongoing changes cannot be designated as regular or not, since they are not complete. However, one can reference the typical characteristics of a change to project whether it will be regular or not. That is, a phonetically gradual change with clear phonetic conditioning falls into Labov’s first type, and thus we can project its regularity


2.1. American English t/d deletion

Consider the deletion of final /t/ and /d/ in American English, which occurs most commonly in words ending in a consonant plus /t/ or /d/, such as just, perfect, child, or grand. This much-studied variable process has been shown to be affected by the preceding and following consonant, with more deletion in a consonant environment; by grammatical status, with less deletion if the /t/ or /d/ is the regular past tense; and by social and age factors, with more deletion among younger, lower socioeconomic class speakers (Labov 1972; Neu 1980).

(...) I found that deletion occurred more in high-frequency words. (...)


3. Changes that affect low-frequency words first

As previously mentioned, Hooper (1976) noted a lexical diffusion paradox: sound change seems to affect high-frequency words first, but analogical change affects low-frequency words first. The first tendency has already been documented. The second tendency is evident in the fact that low-frequency verbs, such as weep/wept, leap/leapt, creep/crept, are regularizing, while high-frequency verbs with the same pattern show no such tendency: that is, keep/kept, sleep/slept, leave/left show no evidence of regularizing. Hooper (1976) argued that changes affecting high-frequency words first have their source in the automation of production, whereas changes affecting low-frequency words first are due to imperfect learning. In the latter category are changes that affect words that do not conform to the general patterns of the language. Such exceptional words can be learned and maintained in their exceptional form if they are of high frequency in the input and in general use. However, if their frequency of use is low, they may not be sufficiently available in experience to be acquired and entrenched. Thus they may be subject to changes based on the general patterns of the language.



4. Modeling phonetic and lexical gradualness

The view of lexical diffusion espoused by both Wang and Labov assumes that a change that diffuses gradually through the lexicon must be phonetically abrupt. This is a necessary assumption if one is to accept a synchronic phonological theory that has phonemic underlying representations. Words can change one by one only if the change is a substitution of phonemes in such a theory. The discovery that sound change can be both phonetically gradual and lexically gradual forces a different view of the mental representation of the phonology of words (Hooper 1981; Bybee 2000b). If subphonemic detail or ranges of variation can be associated with particular words, an accurate model of phonological representation must allow phonetic detail in the cognitive representation of words. A recent proposal is that the cognitive representation of a word can be made up of the set of exemplars that have been experienced by the speaker/hearer. Thus all phonetic variants of a word are stored in memory and organized into a cluster: exemplars that are more similar are closer to one another than to ones that are dissimilar, and exemplars that occur frequently are stronger than less frequent ones (Johnson 1997; Bybee 2000a, 2001; Pierrehumbert 2001). These exemplar clusters, which represent autonomous words, change as experience with language changes. Repeated exemplars within the cluster grow stronger, and less frequently used ones may fade over time, as other memories do.

Changes in the phonetic range of the exemplar cluster may also take place as language is used and new tokens of words are experienced. Thus the range of phonetic variation of a word can gradually change over time, allowing a phonetically gradual sound change to affect different words at different rates. Given a tendency for reduction during production, the phonetic representation of a word will gradually accrue more exemplars that are reduced, and these exemplars will become more likely to be chosen for production, where they may undergo further reduction, gradually moving the words of the language in a consistent direction. The more frequent words will have more chances to undergo online reduction and thus will change more rapidly. The more predictable words (which are usually also the more frequent ones) will have a greater chance of having their reduced version chosen, given the context, and thus will advance the reductive change more rapidly.

The exemplar clusters are embedded in a network of associations among words that map relations of similarity at all levels. Distinct words with similar phonetic properties are associated, as are words with shared semantic features. I have shown in (Bybee 1985, 1988) that morphemes and morphological relations in such a network emerge from parallel phonetic and semantic associations and that schemas or abstractions over relations of similarity can be formulated to account for the regularities and patterns evident in language use.

(...)

An important property of the exemplar model is the emphasis on words as storage units. Various models have proposed that even multi-morphemic words have lexical listing. Vennemann (1974) argued that appropriate constraints on syllable structure can only be applied to whole words, not to morphemes. The common objection to this proposal made in the 1970s was that the human brain does not have sufficient storage capacity for all the words of a language, especially a language with large morphological paradigms. This argument has now been dismissed with the discovery of the huge amount of detail that the brain is capable of recording. Moreover, newer conceptions of the lexicon, not as a list but as a network with tight interconnections, provide the insight that listing two related words, such as start, started, does not take up as much cognitive space as listing two unrelated words, such as start, flower (Bybee 1985). Thus connectionist models (Rumelhart and McClelland 1986) and analogical models (Skousen 1989, 1992; Eddington 2000) have storage of whole words with morphological relations emergent from the categorization involved in storage. In addition, the lexical diffusion data provide evidence that multi-morphemic words can have lexical storage. As we saw in table 11.3, high-frequency regular past-tense English verbs are more likely to have their final /t/ or /d/ deleted than are low-frequency regular verbs. In order for a frequency effect to accrue to a word, that word must exist in memory storage. Since multi-morphemic words evince frequency effects, they must be stored in the lexicon. (...)



5. The effect of frequency of use in context

Given that the exemplar model tracks tokens of use and the exemplar cluster changes according to the phonetic shape of these tokens, it follows that if the context of use affects the phonetic shape of a word, the exemplar cluster will change accordingly. The effect of context can be best exemplified in changes that take place around word or morpheme boundaries, where the segment affected by the change is sometimes in the context for the change and sometimes not. Timberlake (1978) called this an alternating environment. Since the exemplar model registers phonetic tokens, the probabilities inherent in the alternating environment affect the shape of the exemplar cluster. (...) The exemplar cluster, then, appears to reorganize itself, with the stronger exemplars being more frequently chosen for use than the less frequent ones despite the context.

Thus along with the general measure of frequency of use, the relative frequency of the immediate linguistic context of use can also affect the lexical diffusion of a sound change. Even holding frequency constant, a word that occurs more often in the right context for a change will undergo the change more rapidly than a word that occurs less often in the conditioning context.

(...)



8. Consequences for a usage-based theory 

The study of the diffusion of sound change in the lexicon contributes to a better understanding of the nature and causes of sound change. Changes that affect high-frequency words first are a result of the automation of production, the normal overlap and reduction of articulatory gestures that comes with fluency (Browman and Goldstein 1992; Mowrey and Pagliuca 1995). The strong directionality of such changes indicates that they are not the result of random variation, but that they stem from reduction processes resulting from repetition and the normal automation of motor activity. If a sound change does not proceed from the most frequent to the least frequent words, then we should seek its explanation in some other mechanisms of change.

Moreover, I have proposed a model in which variation and change are not external to the lexicon and grammar but inherent to it (Pierrehumbert 1994). Sound change is not rule addition—something that happens at a superficial level without any effect on the deeper reaches of grammar. Rather, lexical representations are affected from the very beginnings of the change. Indeed, they supply an ongoing record of the change since they track the details of the phonetic tokens experienced. Further evidence for sound change having an immediate impact on representation is the fact that sound changes are never reversed or undone (Cole and Hualde 1998; Bybee 2001). The morphological structure of words also plays a role from the initial stages of a change, but less because morphemes have some special status with respect to change and more because of the contexts in which they appear. Alternating contexts retard change, while uniform ones allow change to hurry ahead.

Effects of frequency and context demonstrate that language use has an effect on mental representations. In this view, representations and the grammatical structure that emerges from them are based on experience with language. New linguistic experiences are categorized in terms of already-stored representations, adding to the exemplar clusters already present and, at times, changing them gradually. Various levels of abstraction emerge as exemplars are categorized by phonological and semantic similarity—morphemes, words, phrases, and constructions can all be seen as the result of the categorization of linguistic experiences.