Economy of Effort or Maximum Rate of Information? Exploring Basic Principles of Articulatory Dynamics

Abstract

Economy of effort, a popular notion in contemporary speech research, predicts that dynamic extremes such as the maximum speed of articulatory movement are avoided as much as possible and that approaching the dynamic extremes is necessary only when there is a need to enhance linguistic contrast, as in the case of stress or clear speech. Empirical data, however, do not always support these predictions. In the present study, we considered an alternative principle: maximum rate of information, which assumes that speech dynamics are ultimately driven by the pressure to transmit information as quickly and accurately as possible. For empirical data, we asked speakers of American English to produce repetitive syllable sequences such as wawawawawa as fast as possible by imitating recordings of the same sequences that had been artificially accelerated and to produce meaningful sentences containing the same syllables at normal and fast speaking rates. Analysis of formant trajectories shows that dynamic extremes in meaningful speech sometimes even exceeded those in the nonsense syllable sequences but that this happened more often in unstressed syllables than in stressed syllables. We then used a target approximation model based on a mass-spring system of varying orders to simulate the formant kinematics. The results show that the kind of formant kinematics found in the present study and in previous studies can only be generated by a dynamical system operating with maximal muscular force under strong time pressure and that the dynamics of this operation may hold the solution to the long-standing enigma of greater stiffness in unstressed than in stressed syllables. We conclude, therefore, that maximum rate of information can coherently explain both current and previous empirical data and could therefore be a fundamental principle of motor control in speech production.

Dynamic Formant Trajectories in German Read Speech: Impact of Predictability and Prominence

“…While there are vast differences in formant movement depending on vowel duration, with longer vowels showing more formant movement than shorter vowels, the effect of stress on this relation appears to be small. This observation is partially in line with work that highlights the importance of time as a crucial factor for articulatory effort (Xu and Prom-on, 2010). The authors found that time constraints determine how much information speakers can convey in a conversational turn and hypothesized that speakers maximize their articulatory effort in unstressed vs. stressed vowels, which can also lead to increased dynamics for unstressed vowels compared to stressed vowels.…”

Syllable is a synchronization mechanism that makes human speech possible

“…(Xu, 2009). Secondly, given the frequent occurrence of truncation due to the extrinsic factors (Xu & Prom-on, 2019) and the fact that any degree of truncation is possible (even up to 100%, e.g., in case of syllable contraction: Cheng & Xu, 2013), target approximation is rarely a 0-360º full cycle. Thus it is inappropriate to model intergestural alignment in terms of phase relations such as being in-phase or anti-phase (Nam et al, 2009).…”

“…This would be a further reason, in addition to those listed in Table 1, against modeling Dispalsment Time motor synchrony as physical entrainment. Finally, the massive range of possible truncation (Cheng & Xu, 2013;Xu & Prom-on, 2019) would make it impossible to control duration through articulatory strength (Byrd et al, 2000;Edwards, Beckman & Fletcher, 1991), because, for example, it is inconceivable that an extreme shortening of a segment or syllable up to full elimination is achieved by a maximum increase of stiffness.…”

“…This vulnerability means that syllable onset is the only temporal location for generating reliable tactile input. Furthermore, because target approximation is frequently uncompleted (Xu & Prom-on, 2019), and different syllabic components may have different degrees of incomplete approximation, synchronizing their offsets would be hard. Most importantly, syllable offset is also the onset of the next syllable which already provides a synchronization point.…”

Planting the seed for sound change: Evidence from real-time MRI of velum kinematics in German

“…The measurement and interpretation of stiffness in this study are intended in the sense of a conventional mass-spring equation (i.e. stiffness = the ratio of force to displacement), as adopted by articulatory phonology(Ostry & Munhall 1985, Xu & Prom-on 2019, and do not necessarily relate directly to muscle stiffness. SeeFuchs et al 2011 for a critique of estimating gestural stiffness under the assumptions of a linear second-order system.…”