Phonology without Phonemes

1. Phonology withoutPhonemes Jay McClelland Carnegie Mellon University

2. Collaborators • Cathy Harris • Gary Lupyan • Lori Holt • Brent Vander Wyk • Joan Bybee

3. The Compositional View of Language (Fodor and Pylyshyn, 1988) • Linguistic objects may be atoms or more complex structures like molecules. • Molecules are formed by combining atoms according to rules. • Rules determine which compound structures are allowable and which are not. • Voicing must agree among obstruents at the beginnings and ends of words • *sboke, *tafz

4. One Very Basic Problem:How many units are there? • Words • cut, cut in, cut out, cut it out • Another, a whole nother • Morphemes • Pretend, predict, prefer • Phonemes • Teach, boy, hint • Memory, different • What happened to you?

5. Some units in nature • How many mountains?

6. x x x x x x

7. An Alternative Conceptualization • Language like nature, is clumpy, exhibits varying degrees of discreteness of elements. • Language is only quasi-compositional at all levels, e.g., features, segments, syllables, morphemes, words, phrases, and sentences. • It is often useful as a descriptive approximation to adopt the notion that language consists of units. • But language processing, language learning and language change do not depend on such descriptions. • Itemization, hierarchical classification, and definition of units are meta-linguistic activities. How much language is actually influenced by these activities is an open question.

8. Many connectionist models rely on distributed internal representations in which there is no discrete representation of linguistic units. To date most of them have adopted some sort of concession to units in their inputs and outputs. Word reading models are clear cases in point (e.g. Plaut, McClelland, Seidenberg, and Patterson). Model learns to map from letters to sounds. Input units stand for graphemes (B, PH, EA) Output units stand for phonemes (/b/, /f/, /i/) What do hidden units stand for? Units in Connectionist Models

9. pint bread hint dent Model captures patterns associated with ‘units’ of different scopes without explicitly representing them. • Model learns basic regular correspondences, generalizes appropriately to non-words. • mint, rint; seat, reat; rave, mave… • It learns to produce the correct output for all exceptions in the corpus. • pint, bread, have, etc… • It is sensitive to sub-regularities such as special vowels with certain word-final clusters, ‘e’ conditioning effects, etc • sold, nold • book, grook • rag, dag / rage, dage • Shows graded sensitivity modulated by frequency to item-specific, rhyme-specific, and context-sensitive correspondences. Error / Settling Time High LowFrequency

10. Units and Rules as Emergents • Units, as well as rules, are emergent properties that admit of matters of degree. • We can choose to talk about such things as though they have an independent existence for descriptive convenience but they have no mechanistic role in language processing, language learning, language structure, or language change. • Although many models use ‘units’ in their inputs and outputs, this is for simplicity. • Models using completely continuous inputs and outputs are becoming more common (Elman, ~1988; Plaut and Kello, 2001; Keidel et al, 2003).

11. Phonology without phonemes • Some specific problems with the notions of phoneme and phonetic segment. • Brief sketch of two projects that begin to address some of these difficulties. • Model of gradual language change exhibiting pressure to be regular and to be brief. • Steps toward a gestural theory of the rhymes of English monosyllables.

12. Some of the Problems with Segments in Phonology • Enumeration of segment types is fraught with problems. • No universal inventory; there are cross-language similarities of segments but every segment is different in every language (Pierrehumbert, 2001). • Presence/absence of aspects of articulation is a matter of degree. • Nasal ‘segment’, release burst, duration /degree of approximation to closure in l’s, d’s and t’s… • When we speak the realization of each “segment” depends on • Phonetic context • Word frequency and familiarity • Degree of morphological compositionality, which depends on frequency • Number of neighbors • Language change involves a gradual process of reduction/adjustment. Segments disappear/adjust gradually, not discretely. • What is it half way through the change? • The approach misses out on some of the global structure of words that needs to be taken into account in any theory of word phonology.

13. /t/ segments in two adverbs (Hay, 2002) Softly Swiftly /t/ is less strongly articulated when freq(Adv) > freq(Adj)

14. Just a Few of the Problems with Segments in Phonology • Enumeration of segment types is fraught with problems. • No universal inventory; there are cross-language similarities of segments but every segment is different in every language (Pierrehumbert, 2001). • Presence/absence of aspects of articulation is a matter of degree. • Nasal ‘segment’, release burst, duration /degree of approximation to closure in l’s, d’s and t’s… • When we speak the realization of each “segment” depends on • Phonetic context • Word frequency and familiarity • Degree of morphological compositionality, which depends on frequency • Number of neighbors • Language change involves a gradual process of reduction/adjustment. Segments disappear/adjust gradually, not discretely. • What is it half way through the change? • The approach misses out on some of the global structure of words that needs to be taken into account in any theory of word phonology.

15. Voiced and Unvoiced Rhymes (Bybee, 2001; Bird et al 2003) • Oscillograms are shown at left for ‘he’, ‘heed’ and ‘heat’. • All are about equally long • Vowel and onset are compressed when additional elements are added. • In voiced rhymes (heed) • Vowel remains quite long; other aspects of word are drastically shortened. • In unvoiced rhymes (heat) • The vowel is drastically compressed, leaving more room for other elements.

16. A model of Change that Produces Quasi-Regular Past Tenses (with Gary Lupyan, 2003 Cog Sci Proceedings) • We focused on quasi-regular exceptions: • Items that add /d/ or /t/ and reduce the vowel: • Did, made, had, said, kept, heard, fled… • Items already ending in /d/ or /t/ that change (usually reduce) the vowel: • hid, slid, sat, read, bled, fought.. • We suggest these items reflect historical change sensitive to: • Pressure to be brief contingent on comprehension • Consistency in mapping between sound and meaning • Model involved units that stand for phonemes (against belief) but where presence/absence was a matter of degree. • Constrains were used to alter the degree of presence of a phoneme in the representation, contingent on above pressures.

17. Simulation of Reductive Irregularization Effects • In English, frequent items are less likely to be regular. • Also, d/t items are less likely to be regular. • We found the same effects in a simulation which started with an all-regular corpus. • Changes generally involve more reduction of one or more stem consonsants that the inflectional d/t. • Reduction is actually a matter of degree dependent on frequency, consistent with data (Losiewicz, 1992)

18. Toward a unitless linguistic theory of the spoken word (with Brent Vander Wyk) • Rather than thinking of a word as a sequence of segments, we think of it as a continuous coordinated movement. • This view is not to be confused with the gestural theory of Browman and Goldstein, since we focus directly on the overt articulatory pattern and the corresponding auditory waveform, and do not assume an underlying ‘score’ composed of distinct phonemic targets. • We focus on the rhymes (vowel plus any subsequent closure gesture) of monomorphemic monosyllabic words, temporarily ignoring their onsets. • Can we account for the relative frequencies of different rhyme-types in English (British RP as documented in CELEX) based on a theory that refers to the characteristics of the continuous coordinated movement?

19. Affordances of different rhyme types • As a first approximation, rhymes of stresssed monomorphemic monosylables have a fixed total duration. • With no final closure (he) there’s room for onsets of varying complexity. • Such rhymes are very fully utilized in English (about 36 different words per long vowel). • In rhymes ending in voiced consonants, the vowel is only shortened a little, leaving little room for additional material. • The vowel is much shorter in unvoiced rhymes, so there is more room for additional consonants. • Long require more ‘space’ than short, reducing the possibilities for additional consonants.

20. The nature of word-final closure gestures • Word-final closure gestures involve a progression from very open to some level of closure, which may or may not be complete, and may or may not be followed by a release burst or frication. • l, n, d, ld, nd • s, st, lt, nt, ls • Complexity increases when there are multiple aspects present in the gesture • Duration and degree of articulation of different aspects of the gesture are continuous and subject to compression or expansion depending on other aspects of the word.

21. Coronal, non-coronal, and compound closures • Most rhymes involve a closure with only one articulator (tip of tongue, body of tongue, or lips). • Using the tongue tip to make the word-final closure is quicker than using other articulators (tongue body, lips) and is relatively less compressive to everything else. These can occur with long vowels even when complex (nd, ld, nt, lt, st). • Non-coronal gestures are severely constrained in many contexts and tend to be less compatible with long vowels, likely because they require more extensive movement (mass and/or distance). • Compound closure events (kt, pt, sk, sp, ps, ks, ft, lp, lk) are generally rare. • When there is a compound closure, one of the closures is always coronal. • Such complex closures do not occur with long vowels (only 2 known exceptions). • Regular past tense and plural use word-final coronal (in a wider range of contexts than allowed in mono-morphemic words).

22. Vander Wyk and McClelland Model (See Poster Friday, #36) • Graded constraints cumulate to determine ‘badness’ of rhyme • Voiced closure vs. unvoiced • Long vowel vs. short • Velar or Labial vs. Coronal • +nasal • +lateral (/l/) • +pre-closure s, post-closure s, or post-closure t. • Less good rhymes predicted to occur less frequently • Enough badness can accumulate to prevent a rhyme from occurring at all. • Model accounts for ~85% of variance in frequencies of occurring forms. • Rules out most forms that do not occur; rules in most forms that do occur. • Discrepancies are generally small

23. Gestures after short vowels: Gestures after long vowels: Full Closure Gestures: Linear threshold model of rhyme-type frequencies N = [X – (long V) – (voiced) – (tip, back or lips) – (nasal, lateral, pre-closure fric, post-closure fric, post-closure /t/)] Number of words with given rhyme type Unvoiced Rhyme Voiced Rhyme Two-obst. Unv. Rhyme

24. Gestures after short vowels: Gestures after long vowels: Full Closure Gestures: Number of word types per vowel Long vowel only Model accounts for 90% of variance Some discrepancies noted with arrows Number of words with given rhyme type Unvoiced Rhyme Voiced Rhyme Two-obst. Unv. Rhyme

25. Where do we go from here? • Address discrepancies as possible products of particular combinations of aspects of the articulation. • Take note of differences in the way context effects the details of the articulation (lp, lk, lt). • Consider history and redistribution effects. • Develop a mechanistic instantiation of the account, using a model that produces continuous articulatory gestures and incorporates: • the physical constraints operating on the articulators • the auditory consequences of articulation. • Eliminate phonemes from language change model. • Examine language change as gradual alteration of the way we speak, incorporating a reductive process. • Incorporate influence of frequency, neighborhood, etc. • Extend the effort to eliminate units upward through the morpheme and syllable level to word, phrase, and sentence… • But that is a whole nother story!