77 research outputs found
Neural Decoding of Bistable Sounds Reveals an Effect of Intention on Perceptual Organization.
Auditory signals arrive at the ear as a mixture that the brain must decompose into distinct sources based to a large extent on acoustic properties of the sounds. An important question concerns whether listeners have voluntary control over how many sources they perceive. This has been studied using pure high (H) and low (L) tones presented in the repeating pattern HLH-HLH-, which can form a bistable percept heard either as an integrated whole (HLH-) or as segregated into high (H-H-) and low (-L-) sequences. Although instructing listeners to try to integrate or segregate sounds affects reports of what they hear, this could reflect a response bias rather than a perceptual effect. We had human listeners (15 males, 12 females) continuously report their perception of such sequences and recorded neural activity using MEG. During neutral listening, a classifier trained on patterns of neural activity distinguished between periods of integrated and segregated perception. In other conditions, participants tried to influence their perception by allocating attention either to the whole sequence or to a subset of the sounds. They reported hearing the desired percept for a greater proportion of time than when listening neutrally. Critically, neural activity supported these reports; stimulus-locked brain responses in auditory cortex were more likely to resemble the signature of segregation when participants tried to hear segregation than when attempting to perceive integration. These results indicate that listeners can influence how many sound sources they perceive, as reflected in neural responses that track both the input and its perceptual organization.SIGNIFICANCE STATEMENT Can we consciously influence our perception of the external world? We address this question using sound sequences that can be heard either as coming from a single source or as two distinct auditory streams. Listeners reported spontaneous changes in their perception between these two interpretations while we recorded neural activity to identify signatures of such integration and segregation. They also indicated that they could, to some extent, choose between these alternatives. This claim was supported by corresponding changes in responses in auditory cortex. By linking neural and behavioral correlates of perception, we demonstrate that the number of objects that we perceive can depend not only on the physical attributes of our environment, but also on how we intend to experience it
Second waves, social distancing, and the spread of COVID-19 across America
We recently described a dynamic causal model of a COVID-19 outbreak within a
single region. Here, we combine several of these (epidemic) models to create a
(pandemic) model of viral spread among regions. Our focus is on a second wave
of new cases that may result from loss of immunity--and the exchange of people
between regions--and how mortality rates can be ameliorated under different
strategic responses. In particular, we consider hard or soft social distancing
strategies predicated on national (Federal) or regional (State) estimates of
the prevalence of infection in the population. The modelling is demonstrated
using timeseries of new cases and deaths from the United States to estimate the
parameters of a factorial (compartmental) epidemiological model of each State
and, crucially, coupling between States. Using Bayesian model reduction, we
identify the effective connectivity between States that best explains the
initial phases of the outbreak in the United States. Using the ensuing
posterior parameter estimates, we then evaluate the likely outcomes of
different policies in terms of mortality, working days lost due to lockdown and
demands upon critical care. The provisional results of this modelling suggest
that social distancing and loss of immunity are the two key factors that
underwrite a return to endemic equilibrium.Comment: Technical report: 35 pages, 14 figures, 1 tabl
Dynamic causal modelling of immune heterogeneity
An interesting inference drawn by some Covid-19 epidemiological models is
that there exists a proportion of the population who are not susceptible to
infection -- even at the start of the current pandemic. This paper introduces a
model of the immune response to a virus. This is based upon the same sort of
mean-field dynamics as used in epidemiology. However, in place of the location,
clinical status, and other attributes of people in an epidemiological model, we
consider the state of a virus, B and T-lymphocytes, and the antibodies they
generate. Our aim is to formalise some key hypotheses as to the mechanism of
resistance. We present a series of simple simulations illustrating changes to
the dynamics of the immune response under these hypotheses. These include
attenuated viral cell entry, pre-existing cross-reactive humoral
(antibody-mediated) immunity, and enhanced T-cell dependent immunity. Finally,
we illustrate the potential application of this sort of model by illustrating
variational inversion (using simulated data) of this model to illustrate its
use in testing hypotheses. In principle, this furnishes a fast and efficient
immunological assay--based on sequential serology--that provides a (i)
quantitative measure of latent immunological responses and (ii) a Bayes optimal
classification of the different kinds of immunological response (c.f., glucose
tolerance tests used to test for insulin resistance). This may be especially
useful in assessing SARS-CoV-2 vaccines
Effective immunity and second waves: a dynamic causal modelling study
This technical report addresses a pressing issue in the trajectory of the
coronavirus outbreak; namely, the rate at which effective immunity is lost
following the first wave of the pandemic. This is a crucial epidemiological
parameter that speaks to both the consequences of relaxing lockdown and the
propensity for a second wave of infections. Using a dynamic causal model of
reported cases and deaths from multiple countries, we evaluated the evidence
models of progressively longer periods of immunity. The results speak to an
effective population immunity of about three months that, under the model,
defers any second wave for approximately six months in most countries. This may
have implications for the window of opportunity for tracking and tracing, as
well as for developing vaccination programmes, and other therapeutic
interventions.Comment: 20 pages, 8 figures, 3 tables (technical report
A Sound-Sensitive Source of Alpha Oscillations in Human Non-Primary Auditory Cortex
Copyright © 2019 Billig, Herrmann et al. The functional organization of human auditory cortex can be probed by characterizing responses to various classes of sound at different anatomical locations. Along with histological studies this approach has revealed a primary field in posteromedial Heschl\u27s gyrus (HG) with pronounced induced high-frequency (70-150 Hz) activity and short-latency responses that phase-lock to rapid transient sounds. Low-frequency neural oscillations are also relevant to stimulus processing and information flow, however, their distribution within auditory cortex has not been established. Alpha activity (7-14 Hz) in particular has been associated with processes that may differentially engage earlier versus later levels of the cortical hierarchy, including functional inhibition and the communication of sensory predictions. These theories derive largely from the study of occipitoparietal sources readily detectable in scalp electroencephalography. To characterize the anatomical basis and functional significance of less accessible temporal-lobe alpha activity we analyzed responses to sentences in seven human adults (4 female) with epilepsy who had been implanted with electrodes in superior temporal cortex. In contrast to primary cortex in posteromedial HG, a non-primary field in anterolateral HG was characterized by high spontaneous alpha activity that was strongly suppressed during auditory stimulation. Alpha-power suppression decreased with distance from anterolateral HG throughout superior temporal cortex, and was more pronounced for clear compared to degraded speech. This suppression could not be accounted for solely by a change in the slope of the power spectrum. The differential manifestation and stimulus-sensitivity of alpha oscillations across auditory fields should be accounted for in theories of their generation and function.SIGNIFICANCE STATEMENT To understand how auditory cortex is organized in support of perception, we recorded from patients implanted with electrodes for clinical reasons. This allowed measurement of activity in brain regions at different levels of sensory processing. Oscillations in the alpha range (7-14 Hz) have been associated with functions including sensory prediction and inhibition of regions handling irrelevant information, but their distribution within auditory cortex is not known. A key finding was that these oscillations dominated in one particular non-primary field, anterolateral Heschl\u27s gyrus, and were suppressed when subjects listened to sentences. These results build on our knowledge of the functional organization of auditory cortex and provide anatomical constraints on theories of the generation and function of alpha oscillations
Common Fronto-temporal Effective Connectivity in Humans and Monkeys
Cognitive pathways supporting human language and declarative memory are thought to have uniquely evolutionarily differentiated in our species. However, cross-species comparisons are missing on site-specific effective connectivity between regions important for cognition. We harnessed a new approach using functional imaging to visualize the impact of direct electrical brain stimulation in human neurosurgery patients. Applying the same approach with macaque monkeys, we found remarkably comparable patterns of effective connectivity between auditory cortex and ventro-lateral prefrontal cortex (vlPFC) and parahippocampal cortex in both species. Moreover, in humans electrical tractography revealed rapid evoked potentials in vlPFC from stimulating auditory cortex and speech sounds drove vlPFC, consistent with prior evidence in monkeys of direct projections from auditory cortex to vocalization responsive regions in vlPFC. The results identify a common effective connectivity signature that from auditory cortex is equally direct to vlPFC and indirect to the hippocampus (via parahippocampal cortex) in human and nonhuman primates
Common Fronto-temporal Effective Connectivity in Humans and Monkeys
Human brain pathways supporting language and declarative memory are thought to have differentiated substantially during evolution. However, cross-species comparisons are missing on site-specific effective connectivity between regions important for cognition. We harnessed functional imaging to visualize the effects of direct electrical brain stimulation in macaque monkeys and human neurosurgery patients. We discovered comparable effective connectivity between caudal auditory cortex and both ventro-lateral prefrontal cortex (VLPFC, including area 44) and parahippocampal cortex in both species. Human-specific differences were clearest in the form of stronger hemispheric lateralization effects. In humans, electrical tractography revealed remarkably rapid evoked potentials in VLPFC following auditory cortex stimulation and speech sounds drove VLPFC, consistent with prior evidence in monkeys of direct auditory cortex projections to homologous vocalization-responsive regions. The results identify a common effective connectivity signature in human and nonhuman primates, which from auditory cortex appears equally direct to VLPFC and indirect to the hippocampus
Keeping doors open: transnational families and curricular nationalism
This paper reviews sociological literature to explore the challenge transnational populations pose for nation-based curriculum, and vice versa. With increasing access to dual citizenship and temporary migration, more people are living transnational lifestyles. This poses new challenges in raising the transnational child. Transnationalism has emerged âbottom-upâ from individualised choices and circumstances rather than âtop-downâ through institutional strategy. As a result, education sectors are yet to respond with a reoriented curriculum that can accommodate polycentric lives. This paper adapts Beckâs critique of methodological nationalism and proposes a parallel concept in the curricular nationalism underpinning much official curriculum. It then reviews literature reporting on three curricular experiments that seek to cultivate citizenships above and beyond the nation. While such transcendent designs on citizenship unsettle curricular nationalism, they fail to address the specificities of transnational childâs memberships both here and there. The pedagogic principle of âconnectednessâ is retooled as a pragmatic way forward
Truth after post-truth: for a Strong Programme in Discourse Studies
Contemporary post-truth discourses put the constructivist foundations of Discourse Studies to a test. According to critical observers, discourse analysts have been playing into the hands of Trump, Brexit and right-wing populists by politicising scientific knowledge and undermining the idea of scientific truth. In order to respond to these concerns, this article outlines a Strong Programme in Discourse Studies. While the Strong Programme insists on truths as discursive constructions, in no way does it claim that all ideas have the same truth value or that an idea can become true because somebody wants it to be true. The Strong Programme makes the case for discourse research that is constructivist (it asks how truths are constructed practically) without being relativist (all ideas do not have the same normative quality). Taking inspiration from debates in Science and Technology Studies of the 1970s, the Strong Programme formulates principles for discourse researchers dealing with conflicting truth claims. Discourse analytical explanations of truths of first-order participants and of second-order observers should be symmetrical, heterogeneous, multi-perspectival and reflexive. The Strong Programme discourse research is grounded in the founding traditions of ?French? and ?Critical? Discourse Studies, which have struggled over questions of truth and reality since the beginning. While critically interrogating the structuralist heritage of these strands, the Strong Programme insists on the practices of making and unmaking ideas through language use no matter whether they appear as true or false to participants and observers. Discourse Studies are encouraged to critically reflect on how hierarchies between knowledges are not only represented but, through their representation, also constituted through discursive practices
- âŠ