Academic journal article Perception and Psychophysics

Perception of Rhythmic Grouping: Testing the Iambic/trochaic Law

Academic journal article Perception and Psychophysics

Perception of Rhythmic Grouping: Testing the Iambic/trochaic Law

Article excerpt

This study was designed to test the iambic/trochaic law, which claims that elements contrasting in duration naturally form rhythmic groupings with final prominence, whereas elements contrasting in intensity form groupings with initial prominence. It was also designed to evaluate whether the iambic/trochaic law describes general auditory biases, or whether rhythmic grouping is speech or language specific. In two experiments, listeners were presented with sequences of alternating /ga/ syllables or square wave segments that varied in either duration or intensity and were asked to indicate whether they heard a trochaic (i.e., strong-weak) or an iambic (i.e., weak-strong) rhythmic pattern. Experiment 1 provided a validation of the iambic/trochaic law in English-speaking listeners; for both speech and nonspeech stimuli, variations in duration resulted in iambic grouping, whereas variations in intensity resulted in trochaic grouping. In Experiment 2, no significant differences were found between the rhythmic-grouping performances of English- and French-speaking listeners. The speech/ nonspeech and cross-language parallels suggest that the perception of linguistic rhythm relies largely on general auditory mechanisms. The applicability of the iambic/trochaic law to speech segmentation is discussed.

In order to understand spoken language, listeners must be able to locate lexical items in continuous speech-a process that involves segmenting the speech stream. Although speech segmentation strategies may vary across languages, it has been hypothesized that segmentation tends to be based on linguistic rhythm (Cutler, 1994; Mattys, Jusczyk, Luce, & Morgan, 1999).

Rhythm can generally be characterized as the repetition of patterned sequences of elements, often varying in prominence (Fraisse, 1974, 1982). This characterization applies most strictly to certain forms of music and poetry; however, normal speech also exhibits tendencies toward rhythmic patterning-for example, in the alternation of stressed and unstressed syllables. In addition, listeners may perceptually exaggerate the rhytnmicity of utterances. For example, English-speaking listeners hear interstress intervals as more evenly spaced than they actually are (Darwin & Donovan, 1980; Donovan & Darwin, 1979; Lehiste, 1977).

How might perceived rhythm help listeners to group syllables into word or phrase length units or, equivalently, to detect word or phrase boundaries? One plausible answer is that in segmenting speech, listeners learn to exploit the typical rhythmic patterns of words or phrases in their native language (see, e.g., Cutler, 1994; Mattys et al., 1999). For example, French tends to be segmented by native listeners at the level of the syllable (Cutler, Mehler, Norris, & Segui, 1986; Mehler, Dommergues, Frauenfelder, & Segui, 1981), Japanese listeners rely on the mora for segmenting Japanese (Otake, Hatano, Cutler, & Mehler, 1993), and English is most easily segmented by Anglophones, using a stress-based segmentation strategy (Cutler & Butterfield, 1992; Cutler & Norris, 1988; Echols, Crowhurst, & Childers, 1997).

In most languages, words have fixed or, at least, characteristic stress patterns (Hyman, 1977), and these regularities are obviously informative about likely word boundaries. In word segmentation studies in which artificial languages are used, listeners are most successful when the phonological properties of the artificial language match those of their native language. For example, Vroomen, Tuomainen, and de Gelder (1998) found that the presence of word-initial stress, marked by pitch accent, facilitated word segmentation for native speakers of Finnish and Dutch, languages that have a predominance of word-initial stress. Word-initial stress did not help Frenchspeaking listeners segment the artificial language, possibly because stress rarely occurs on the first syllable of polysyllabic French words (Dell & Vergnaud, 1984). …

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