The cortical organization of speech processing

Despite decades of research, the functional neuroanatomy of speech processing has been difficult to characterize. A major impediment to progress may have been the failure to consider task effects when mapping speech-related processing systems. We outline a dual-stream model of speech processing that remedies this situation. In this model, a ventral stream processes speech signals for comprehension, and a dorsal stream maps acoustic speech signals to frontal lobe articulatory networks. The model assumes that the ventral stream is largely bilaterally organized--although there are important computational differences between the left- and right-hemisphere systems--and that the dorsal stream is strongly left-hemisphere dominant.     

Endogenous cortical rhythms determine cerebral specialization for speech perception and production

Across multiple timescales, acoustic regularities of speech match rhythmic properties of both the auditory and motor systems. Syllabic rate corresponds to natural jaw-associated oscillatory rhythms, and phonemic length could reflect endogenous oscillatory auditory cortical properties. Hemispheric lateralization for speech could result from an asymmetry of cortical tuning, with left and right auditory areas differentially sensitive to spectro-temporal features of speech. Using simultaneous electroencephalographic (EEG) and functional magnetic resonance imaging (fMRI) recordings from humans, we show that spontaneous EEG power variations within the gamma range (phonemic rate) correlate best with left auditory cortical synaptic activity, while fluctuations within the theta range correlate best with that in the right. Power fluctuations in both ranges correlate with activity in the mouth premotor region, indicating coupling between temporal properties of speech perception and production. These data show that endogenous cortical rhythms provide temporal and spatial constraints on the neuronal mechanisms underlying speech perception and production.     

Speech perception: linking comprehension across a cortical network

Listening to speech amidst noise is facilitated by a variety of cues, including the predictable use of certain words in certain contexts. A recent fMRI study of the interaction between noise and semantic predictability has identified a cortical network involved in speech comprehension.     

Large-scale chromatin fibers of living cells display a discontinuous functional organization

We investigated the chromatin organization of living cells with a combination of recently developed approaches for histone and DNA labeling. Nucleosomal DNA was labeled with a histone H2B-GFP (green fluorescent protein) fusion protein and the chromatin organization of living HeLa cells was analyzed by high resolution confocal microscopy. Within the perinuclear and perinucleolar regions chromatin was organized into large-scale fibers of 2 to 8 microm in length and 300 to 500 nm in diameter. Within the nuclear interior we observed similar large-scale fibers, but in addition focal as well as diffuse forms of organization. Comparison with standard labeling and detection procedures revealed major differences in the chromatin organization observed. Chromatin organization revealed by the distribution of histone H2B-GFP was directly compared with the functional organization of chromatin by Cy3-dUTP labeling of DNA replicating at a specific time. DNA regions replicating at a specific time display characteristic physical and functional properties. Analysis of Cy3-labeled foci revealed that they are associated with all three forms of chromatin organization (fibrillar, focal and diffuse). In particular, Cy3-labeled foci appeared as discontinuous regions of large-scale fibers. These results demonstrate that large-scale chromatin fibers have discontinuous functional characteristics.     

Word learning and lexical development across the lifespan

Word learning is one of the core components of language acquisition. In this article, we provide an overview of the theme issue on word learning, describing some of the ways in which research in the area has progressed and diverged. In recent years, word learning has become central in a wider range of research areas, and is important to research on adult, as well as child and infant language. We introduce 10 papers that cover the recent developments from a wide range of perspectives, focusing on developmental research, the influence of reading skills, neuroimaging and the relationship between word learning and general models of memory.     

Determinants of time allocation across the lifespan

This paper lays the groundwork for a theory of time allocation across the life course, based on the idea that strength and skill vary as a function of age, and that return rates for different activities vary as a function of the combination of strength and skills involved in performing those tasks. We apply the model to traditional human subsistence patterns. The model predicts that young children engage most heavily in low-strength/low-skill activities, middle-aged adults in high-strength/high-skill activities, and older adults in low-strength/high-skill activities. Tests among Machiguenga and Piro forager-horticulturalists of southeastern Peru show that males and females focus on low-strength/low-skill tasks early in life (domestic tasks and several forms of fishing), switch to higher-strength/higher-skill activities in their twenties and thirties (hunting, fishing, and gardening for males; fishing and gardening for females), and shift focus to high-skill activities late in life (manufacture/repair, food processing). Michael Gurven is an assistant professor of anthropology at the University of California-Santa Barbara. He received his Ph.D. from the University of New Mexico in 2000. He has conducted fieldwork in Paraguay and Bolivia with Ache and Tsimane forager-horticulturalists. His research interests include intragroup cooperation and problems of collective action, and the application of life history theory to explaining human longevity, cognitive development, delayed maturation, and sociality. Since 2002, Gurven and Kaplan have co-directed the Tsimane Health and Life History Initiative, a five-year project to develop theory and test implications of different models of human life history evolution. Hillard Kaplan is a professor of anthropology at University of New Mexico. He received his Ph.D. from the University of Utah in 1983. He has conducted fieldwork in Paraguay, Brazil, Botswana, and Bolivia. His research interests include evolutionary perspectives on life course development and senescence, and brain evolution. He has launched theoretical and empirical investigations into each of these areas, uniting evolutionary and economic approaches. He has applied human capital theory toward explaining human life history evolution, and the proximate physiological and psychological mechanisms governing fertility and parental investment in both traditional, high-fertility, subsistence economies and modern, low-fertility, industrial societies.     

Auditory perception and the evolution of speech

Among topics related to the evolution of language, the evolution of speech is particularly fascinating. Early theorists believed that it was the ability to produce articulate speech that set the stage for the evolution of the «special» speech processing abilities that exist in modern-day humans. Prior to the evolution of speech production, speech processing abilities were presumed not to exist. The data reviewed here support a different view. Two lines of evidence, one from young human infants and the other from infrahuman species, neither of whom can produce articulate speech, show that in the absence of speech production capabilities, the perception of speech sounds is robust and sophisticated. Human infants and non-human animals evidence auditory perceptual categories that conform to those defined by the phonetic categories of language. These findings suggest the possibility that in evolutionary history the ability to perceive rudimentary speech categories preceded the ability to produce articulate speech. This in turn suggests that it may be audition that structured, at least initially, the formation of phonetic categories.     

Interhemispheric asymmetry of the spatial organization of human cortical potentials during the perception of emotional and indifferent images

In 13 healthy subjects dynamic characteristics of potentials spatial-temporal organization (PSTO) in the cortical left and right hemispheres at presentation of emotionally coloured and indifferent graphic images were studied by the method of quantitative evaluation of subsequent electroencephalotopograms. It is shown that, in contrast to the state of calm alertness, presentation of emotional and indifferent images leads to a decrease of the time of discordance in the hemispheres activity i.e. to synchronization increase. At the action of emotionally coloured images differences were found between the reorganizations of the left and right hemispheres, while there were no such differences at the presentation of indifferent images.     

Lipreading and audio-visual speech perception.

This paper reviews progress in understanding the psychology of lipreading and audio-visual speech perception. It considers four questions. What distinguishes better from poorer lipreaders? What are the effects of introducing a delay between the acoustical and optical speech signals? What have attempts to produce computer animations of talking faces contributed to our understanding of the visual cues that distinguish consonants and vowels? Finally, how should the process of audio-visual integration in speech perception be described; that is, how are the sights and sounds of talking faces represented at their conflux?     

The spatiotemporal dynamics of microglia across the human lifespan

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Born this way: Hippocampal neurogenesis across the lifespan

The capability of the mammalian brain to generate new neurons through the lifespan has gained much attention for the promise of new therapeutic possibilities especially for the aging brain. One of the brain regions that maintains a neurogenesis‐permissive environment is the dentate gyrus of the hippocampus. Here, new neurons are generated from a pool of multipotent neural progenitor cells to become fully functional neurons that are integrated into the brain circuitry. A growing body of evidence points to the fact that neurogenesis in the adult hippocampus is necessary for certain memory processes, and in mood regulation, while alterations in hippocampal neurogenesis have been associated with a myriad of neurological and psychiatric disorders. More recently, evidence has come to light that new neurons may differ in their vulnerability to environmental and disease‐related influences depending on the time during the life course at which they are exposed. Thus, it has been the topic of intense research in recent years. In this review, we will discuss the complex process and associated functional relevance of hippocampal neurogenesis during the embryonic/postnatal period and in adulthood. We consider the implications of hippocampal neurogenesis during the developmentally critical periods of adolescence and older age. We will further consider the literature surrounding hippocampal neurogenesis and its functional role during these critical periods with a view to providing insight into the potential of harnessing neurogenesis for health and therapeutic benefit.     

Sex differences in interest in infants across the lifespan

This study investigated sex differences in interest in infants among children, adolescents, young adults, and older individuals. Interest in infants was assessed with responses to images depicting animal and human infants versus adults, and with verbal responses to questionnaires. Clear sex differences, irrespective of age, emerged in all visual and verbal tests, with females being more interested in infants than males. Male interest in infants remained fairly stable across the four age groups, whereas female interest in infants was highest in childhood and adolescence and declined thereafter, particularly for the responses to visual stimuli. The observed developmental changes in female interest in infants are consistent with the hypothesis that they represent a biological adaptation for parenting. This study was supported by NIH grants R01-MH57249, R01-MH62577, and K02-MH63097. Dario Maestripieri, Ph.D., is an assistant professor of Human Development and Evolutionary Biology at the University of Chicago. He has broad research interests in behavior, development, and evolution, and conducted research on primate parenting and development at the University of Cambridge and at the Yerkes Regional Primate Research Center before moving to Chicago. Suzanne Pelka is a graduate student in Human Development at the University of Chicago.