Grouping helps listeners to break down the speech signal into smaller units. Specific acoustic cues, in particular duration and intensity, have been reported to determine grouping of disyllabic units across languages [Iambic-Trochaic Law (ITL)]. The ITL states that iambic grouping is obtained from syllabic sequences alternating in duration, whereas trochaic grouping is obtained from those alternating in intensity. Speakers of different languages vary in the extent to which they use the ITL. It has been proposed that this linguistic modulation of the ITL relates to cross-linguistic differences in prosody. The present study further investigates the predictions of the ITL in two under-researched languages, Papuan Malay and Akan, for which there is controversy on the existence of word stress. They are compared to German, a well-researched language with variable word stress. A perceptual grouping task used in previous work is replicated with listeners from each language. The results show considerable cross-linguistic differences and shed light on acoustic perceptual properties in Papuan Malay and Akan. The outcomes reconfirm cross-linguistic variability and modulation of the applicability of the ITL across languages.

Young infants can segment continuous speech with acoustic as well as statistical cues. Understanding how these cues interact can be informative about how infants solve the segmentation problem. This study investigates the use of acoustic and statistical cues by both adult French speakers and 6-to-7-month-old French-learning infants. Both groups were familiarized with a naturally recorded string, alternating either in duration (long-short) or in intensity (soft-loud). In addition, statistical cues were present in both strings, signaling different word boundaries than the acoustic cues. The adults were tested in a recognition task and the infants with the Head-turn Preference Procedure. Results show that the French-speaking adults segmented the strings by responding to the acoustic cues in both familiarization conditions, following the predictions of the Iambic-Trochaic Law. In contrast, the French-learning infants displayed segmentation based on TPs in the Intensity condition only. These findings collectively contribute to our understanding of how the use of acoustic and statistical cues to decode linguistic input changes between infancy and adulthood and differs across languages.

Rhythm perception in speech and non-speech acoustic stimuli has been shown to be affected by general acoustic biases as well as by phonological properties of the native language of the listener. The present paper extends the cross-linguistic approach in this field by testing the application of the iambic-trochaic law as an assumed general acoustic bias on rhythmic grouping of non-speech stimuli by speakers of three languages: Arabic, Hebrew and German. These languages were chosen due to relevant differences in their phonological properties on the lexical level alongside similarities on the phrasal level. The results show Iambic-Trochaic-Law (ITL) conforming weak–strong grouping for duration-cued acoustic salience. However, only German participants judged intensity-varying sequences as strong–weak; no grouping preferences were found for speakers of Arabic and Hebrew. Overall these results suggest that prosodic properties of the phonological phrase and of the lexical level of the native language show differing effects on rhythmical grouping.

Listeners parse the speech signal effortlessly into words and phrases, but many questions remain about how. One classic idea is that rhythm-related auditory principles play a role, in particular, that a psycho-acoustic "iambic-trochaic law" (ITL) ensures that alternating sounds varying in intensity are perceived as recurrent binary groups with initial prominence (trochees), while alternating sounds varying in duration are perceived as binary groups with final prominence (iambs). We test the hypothesis that the ITL is in fact an indirect consequence of the parsing of speech along two in-principle orthogonal dimensions: prominence and grouping. Results from several perception experiments show that the two dimensions, prominence and grouping, are each reliably cued by both intensity and duration, while foot type is not associated with consistent cues. The ITL emerges only when one manipulates either intensity or duration in an extreme way. Overall, the results suggest that foot perception is derivative of the cognitively more basic decisions of grouping and prominence, and the notions of trochee and iamb may not play any direct role in speech parsing. A task manipulation furthermore gives new insight into how these decisions mutually inform each other.

English and Mandarin native speakers’ cue-weighting of lexical stress: Results from MMN and LDN

In a sequence of otherwise equal sounds, listeners tend to hear a series of trochees (groups of two sounds with an initial beat) when every other sound is louder; they tend to hear a series of iambs (groups of two sounds with a final beat) when every other sound is longer. The article presents evidence that this so-called "Iambic-Trochaic Law" (ITL) is a consequence of the way listeners parse the signal along two orthogonal dimensions, grouping (Which tone is first/last?) and prominence (Which tone is prominent?). A production experiment shows that in speech, intensity and duration correlate when encoding prominence, but anticorrelate when encoding grouping. A model of the production data shows that the ITL emerges from the cue distribution based on a listener's predicted decisions about prominence and grouping respectively. This, and further predictions derived from the model, are then tested in speech and tone perception. The perception results provide evidence that intensity and duration are excellent cues for grouping and prominence, but poor cues for the distinction between iamb and trochee per se. Overall, the findings illustrate how the ITL derives from the way listeners recover two orthogonal perceptual dimensions, grouping and prominence, from a single acoustic stream. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Abstract This paper presents both distributional and acoustic phonetic evidence for iambic stress in Tetsǫ́t'ıné (ISO: CHP), a Dene (Athapaskan) language with contrastive vowel length and four contrastive tones. In our acoustic study, we find that the primary correlate of stress in Tetsǫ́t'ıné is duration, whereas intensity plays a secondary but statistically significant role. There was no statistically significant effect on F0 in our results. We discuss our results in relation to several proposals regarding the typology of stress systems. Based on the Functional Load Hypothesis (Berinstein 1979) and Dispersion Theory (Flemming 1995, 2001), we find that our results are to some extent unexpected. We suggest that our results are most consistent with the Iambic–Trochaic Law (Hayes 1995), which predicts that iambic stress systems prefer to use duration as their primary stress correlate.

Supplemental Material for Two-Dimensional Parsing of the Acoustic Stream Explains the Iambic–Trochaic Law

Abstract The iambic/trochaic law (ITL) asserts that listeners associate louder sounds with group onsets and longer sounds with group endings. The ITL has interested theoretical phonologists since Hayes' (1995) proposal that it may describe the perceptual underpinnings of the Foot Inventory (Hayes, 1995; McCarthy and Prince, 1986, 1996). This article surveys the growing experimental literature exploring perceptual ITL effects. The experimental findings to date suggest that ITL effects have both a “nature” and a “nurture” component, are documented for a variety of species, and are cross‐modal in humans. Questions are raised as to whether there is likely to be a natural connection between ITL effects and the foot inventory.

Perceptual grouping is fundamental to many auditory processes. The Iambic-Trochaic Law (ITL) is a default grouping strategy, where rhythmic alternations of duration are perceived iambically (weak-strong), while alternations of intensity are perceived trochaically (strong-weak). Some argue that the ITL is experience dependent. For instance, French speakers follow the ITL, but not as consistently as German speakers. We hypothesized that learning about prosodic patterns, like word stress, modulates this rhythmic grouping. We tested this idea by training French adults on a German-like stress contrast. Individuals who showed better phonological learning had more ITL-like grouping, particularly over duration cues. In a non-phonological condition, French adults were trained using identical stimuli, but they learned to attend to acoustic variation that was not linguistic. Here, no learning effects were observed. Results thus suggest that phonological learning can modulate low-level auditory grouping phenomena, but it is constrained by the ability of individuals to learn from short-term training.

The influence of varying vowel phonation and duration on rhythmic grouping biases among Spanish and English speakers

Speech segmentation is supported by multiple sources of information that may either inform language processing specifically, or serve learning more broadly. The Iambic/Trochaic Law (ITL), where increased duration indicates the end of a group and increased emphasis indicates the beginning of a group, has been proposed as a domain-general mechanism that also applies to language. However, language background has been suggested to modulate use of the ITL, meaning that these perceptual grouping preferences may instead be a consequence of language exposure. To distinguish between these accounts, we exposed native-English and native-Japanese listeners to sequences of speech (Experiment 1) and nonspeech stimuli (Experiment 2), and examined segmentation using a 2AFC task. Duration was manipulated over 3 conditions: sequences contained either an initial-item duration increase, or a final-item duration increase, or items of uniform duration. In Experiment 1, language background did not affect the use of duration as a cue for segmenting speech in a structured artificial language. In Experiment 2, the same results were found for grouping structured sequences of visual shapes. The results are consistent with proposals that duration information draws upon a domain-general mechanism that can apply to the special case of language acquisition.

The Iambic-Trochaic Law (ITL) accounts for speech rhythm, grouping of sounds as either Iambs—if alternating in duration—or Trochees—if alternating in pitch and/or intensity. The two different rhythms signal word order, one of the basic syntactic properties of language. We investigated the extent to which Iambic and Trochaic phrases could be auditorily and visually recognized, when visual stimuli engage lip reading. Our results show both rhythmic patterns were recognized from both, auditory and visual stimuli, suggesting that speech rhythm has a multimodal representation. We further explored whether participants could match Iambic and Trochaic phrases across the two modalities. We found that participants auditorily familiarized with Trochees, but not with Iambs, were more accurate in recognizing visual targets, while participants visually familiarized with Iambs, but not with Trochees, were more accurate in recognizing auditory targets. The latter results suggest an asymmetric processing of speech rhythm: in auditory domain, the changes in either pitch or intensity are better perceived and represented than changes in duration, while in the visual domain the changes in duration are better processed and represented than changes in pitch, raising important questions about domain general and specialized mechanisms for speech rhythm processing.

The Iambic-Trochaic Law (Bolton, 1894; Hayes, 1995; Woodrow, 1909) asserts that listeners associate greater intensity with group beginnings (a loud-first preference) and greater duration with group endings (a long-last preference). Hayes (1987; 1995) posits a natural connection between the prominences referred to in the ITL and the locations of stressed syllables in feet. However, not all lengthening in final positions originates with stressed syllables, and greater duration may also be associated with stress in nonfinal (trochaic) positions. The research described here challenged the notion that presumptive long-last effects necessarily reflect stress-related duration patterns, and investigated the general hypothesis that the robustness of long-last effects should vary depending on the strength of the association between final positions and increased duration, whatever its source. Two ITL studies were conducted in which native speakers of Spanish and of English grouped streams of rhythmically alternating syllables in which vowel intensity and/or duration levels were varied. These languages were chosen because while they are prosodically similar, increased duration on constituent-final syllables is both more common and more salient in English than Spanish. Outcomes revealed robust loud-first effects in both language groups. Long-last effects were significantly weaker in the Spanish group when vowel duration was varied singly. However, long-last effects were present and comparable in both language groups when intensity and duration were covaried. Intensity was a more robust predictor of responses than duration. A primary conclusion was that whether or not humans’ rhythmic grouping preferences have an innate component, duration-based grouping preferences, at least, and the magnitude of intensity-based effects are shaped by listeners’ backgrounds.

Rhythm in music and speech can be characterized by a constellation of several acoustic cues. Individually, these cues have different effects on rhythmic perception: sequences of sounds alternating in duration are perceived as short-long pairs (weak-strong/iambic pattern), whereas sequences of sounds alternating in intensity or pitch are perceived as loud-soft, or high-low pairs (strong-weak/trochaic pattern). This perceptual bias—called the Iambic-Trochaic Law (ITL)–has been claimed to be an universal property of the auditory system applying in both the music and the language domains. Recent studies have shown that language experience can modulate the effects of the ITL on rhythmic perception of both speech and non-speech sequences in adults, and of non-speech sequences in 7.5-month-old infants. The goal of the present study was to explore whether language experience also modulates infants’ grouping of speech. To do so, we presented sequences of syllables to monolingual French- and German-learning 7.5-month-olds. Using the Headturn Preference Procedure (HPP), we examined whether they were able to perceive a rhythmic structure in sequences of syllables that alternated in duration, pitch, or intensity. Our findings show that both French- and German-learning infants perceived a rhythmic structure when it was cued by duration or pitch but not intensity. Our findings also show differences in how these infants use duration and pitch cues to group syllable sequences, suggesting that pitch cues were the easier ones to use. Moreover, performance did not differ across languages, failing to reveal early language effects on rhythmic perception. These results contribute to our understanding of the origin of rhythmic perception and perceptual mechanisms shared across music and speech, which may bootstrap language acquisition.

Language dominance shapes non-linguistic rhythmic grouping in bilinguals

Humans share with non-human animals perceptual biases that might form the basis of complex cognitive abilities. One example comes from the principles described by the iambic-trochaic law (ITL). According to the ITL, sequences of sounds varying in duration are grouped as iambs, whereas sequences varying in intensity are grouped as trochees. These grouping biases have gained much attention because they might help pre-lexical infants bootstrap syntactic parameters (such as word order) in their language. Here, we explore how experience triggers the emergence of perceptual grouping biases in a non-human species. We familiarized rats with either long-short or short-long tone pairs. We then trained the animals to discriminate between sequences of alternating and randomly ordered tones. Results showed animals developed a grouping bias coherent with the exposure they had. Together with results observed in human adults and infants, these results suggest that experience modulates perceptual organizing principles that are present across species.

The Iambic-Trochaic Law (ITL) asserts that listeners associate greater acoustic intensity with group beginnings and greater duration with group endings. Some researchers have assumed a natural connection between these perceptual tendencies and universal principles underlying linguistic categories of rhythm. The experimental literature on ITL effects is limited in three ways. Few studies of listeners' perceptions of alternating sound sequences have used speech-like stimuli, cross-linguistic testing has been inadequate and existing studies have manipulated intensity and duration singly, whereas these features vary together in natural speech. This paper reports the results of three experiments conducted with native Zapotec speakers and one with native English speakers. We tested listeners' grouping biases using streams of alternating syllables in which intensity and duration were varied separately, and sequences in which they were covaried. The findings suggest that care should be taken in assuming a natural connection between the ITL and universal principles of prosodic organisation.

Perceptual attunement to one's native language results in language-specific processing of speech sounds. This includes stress cues, instantiated by differences in intensity, pitch, and duration. The present study investigates the effects of linguistic experience on the perception of these cues by studying the Iambic-Trochaic Law (ITL), which states that listeners group sounds trochaically (strong-weak) if the sounds vary in loudness or pitch and iambically (weak-strong) if they vary in duration. Participants were native listeners either of French or German; this comparison was chosen because French adults have been shown to be less sensitive than speakers of German and other languages to word-level stress, which is communicated by variation in cues such as intensity, fundamental frequency (F0), or duration. In experiment 1, participants listened to sequences of co-articulated syllables varying in either intensity or duration. The German participants were more consistent in their grouping than the French for both cues. Experiment 2 was identical to experiment 1 except that intensity variation was replaced by pitch variation. German participants again showed more consistency for both cues, and French participants showed especially inconsistent grouping for the pitch-varied sequences. These experiments show that the perception of linguistic rhythm is strongly influenced by linguistic experience.

The Estonian language is unique in that it differentiates between three degrees of length in vowels, as well as in consonants. Phonologically, the ternary system of Estonian quantity has been interpreted in a variety of manners, but a generally accepted description has yet to be found. In the present paper, I argue for the approach that overlong segments arise due to foot-final lengthening in monosyllabic feet. Foot-final lengthening is not simply a matter of phonetic implementation. The lengthening may be the result of the addition of a mora at the end of the foot or from the strength of the final mora. I focus my discussion on the second case, which links foot- final lengthening and quantity degrees to the well-known Iambic-Trochaic Law.