Speech Rhythm and Timing

Speech events do not typically exhibit the temporal regularity conspicuous in many musical rhythms. In the absence of such surface periodicity, hierarchical approaches to speech timing propose that nested prosodic domains, such as syllables and stress-delimited feet, can be modelled as coupled oscillators and that surface timing patterns reflect variation in the relative weights of oscillators. Localized approaches argue, by contrast, that speech timing is largely organized bottom-up, based on segmental identity and subsyllabic organization, with prosodic lengthening effects locally associated with domain heads and edges. This chapter weighs the claims of the two speech timing approaches against empirical data. It also reviews attempts to develop quantitative indices (‘rhythm metrics’) of cross-linguistic variations in surface timing, in particular in the degree of contrast between stronger and weaker syllables. It further reflects on the shortcomings of categorical ‘rhythm class’ typologies in the face of cross-linguistic evidence from speech production and speech perception.

The origin and evolution of the euarthropod labrum

A widely (although not universally) accepted model of arthropod head evolution postulates that the problematic labrum, a structure seen in almost all living euarthropods, evolved from an anterior pair of appendages homologous to the frontal appendages of onychophorans. However, the implications of this model for the interpretation of fossil arthropods have not been fully integrated into reconstructions of the euarthropod stem group, which remains in a state of some disorder. Here I review the evidence for the evolution of the labrum from living taxa, and reconsider how fossils should be interpreted in the light of this. Identification of the segmental identity of head appendage in fossil arthropods remains problematic, and often rests ultimately on unproven assertions. New evidence from Parapeytoia is presented to suggest that the labral appendage persisted well up into the upper stem-group of the euarthropods, which prompts a re-evaluation of widely-accepted segmental homologies and the interpretation of fossil central nervous systems. Only a protocerebral brain was present in large part of the euarthropod stem group, and the modern deutocerebrum must have been a relatively late addition.

Why a Constant Number of Vertebrae? - Digital Control of Segmental Identity During Vertebrate Development

It is not understood how the numbers and identities of vertebrae are controlled during mammalian development. The remarkable robustness and conservation of segmental numbers may suggest a digital nature of the underlying process. Here I propose a mechanism that allows cells to obtain and store the segmental information in digital form, and to produce a pattern of chromatin accessibility that in turn regulates Hox gene expression specific to the metameric segment. The model requires that a regulatory element be present such that the number of occurrences of the motif between two consecutive Hox genes equals the number of segments under the control of the anterior gene. This is true for the recently discovered HRC3 motif, associated with histone modifications and developmental genes. The finding not only allows correctly predicting the numbers of segments using only sequence information, but also resolves the 40-year-old enigma of the function of temporal and spatial collinearity of Hox genes. The logic of the mechanism is illustrated in an animated video: https://youtu.be/4a3XOQ7Lz28. I also discuss how different aspects of the proposed mechanism can be tested experimentally.

Establishing sharp and homogeneous segments in the hindbrain

Studies of the vertebrate hindbrain have revealed parallel mechanisms that establish sharp segments with a distinct and homogeneous regional identity. Recent work has revealed roles of cell identity regulation and its relationships with cell segregation. At early stages, there is overlapping expression at segment borders of the Egr2 and Hoxb1 transcription factors that specify distinct identities, which is resolved by reciprocal repression. Computer simulations show that this dynamic regulation of cell identity synergises with cell segregation to generate sharp borders. Some intermingling between segments occurs at early stages, and ectopic egr2-expressing cells switch identity to match their new neighbours. This switching is mediated by coupling between egr2 expression and the level of retinoic acid signalling, which acts in a community effect to maintain homogeneous segmental identity. These findings reveal an interplay between cell segregation and the dynamic regulation of cell identity in the formation of sharp patterns in the hindbrain and raise the question of whether similar mechanisms occur in other tissues.

Stress and Cognitive Functions of Working Women in India

This study assessed the effects of life stress on cognitive functions in working women. In the present scenario role segregated and segmental identity of women has put them in a situation where females have to perform multiple and adapt to diverse kind of psychological environments. They are always under pressure to rearrange their traditional roles of wife, mother and home maker in order to accommodate their non traditional roles as earner. These pressures tend to predispose them to life stresses, sometimes leading to reduced psychological well being. High stress leads to cognitive dysfunctions as more attention is paid to negative aspects of life. Scores of cognitive functions viz. problem solving, focused attention, concentration & recall in low stressed women were significantly higher than these scores in high stress women. Conclusion: Cognitive functions were disrupted in case of high stress women and sharp in case of low stress women

Hox genes and evolution

Hox proteins are a deeply conserved group of transcription factors originally defined for their critical roles in governing segmental identity along the antero-posterior (AP) axis in Drosophila. Over the last 30 years, numerous data generated in evolutionarily diverse taxa have clearly shown that changes in the expression patterns of these genes are closely associated with the regionalization of the AP axis, suggesting that Hox genes have played a critical role in the evolution of novel body plans within Bilateria. Despite this deep functional conservation and the importance of these genes in AP patterning, key questions remain regarding many aspects of Hox biology. In this commentary, we highlight recent reports that have provided novel insight into the origins of the mammalian Hox cluster, the role of Hox genes in the generation of a limbless body plan, and a novel putative mechanism in which Hox genes may encode specificity along the AP axis. Although the data discussed here offer a fresh perspective, it is clear that there is still much to learn about Hox biology and the roles it has played in the evolution of the Bilaterian body plan.