To see the other types of publications on this topic, follow the link: Temporal delay invariance.
Journal articles on the topic 'Temporal delay invariance'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 33 journal articles for your research on the topic 'Temporal delay invariance.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Isik, Leyla, Andrea Tacchetti, and Tomaso Poggio. "A fast, invariant representation for human action in the visual system." Journal of Neurophysiology 119, no. 2 (February 1, 2018): 631–40. http://dx.doi.org/10.1152/jn.00642.2017.
Full textAbstract:
Humans can effortlessly recognize others’ actions in the presence of complex transformations, such as changes in viewpoint. Several studies have located the regions in the brain involved in invariant action recognition; however, the underlying neural computations remain poorly understood. We use magnetoencephalography decoding and a data set of well-controlled, naturalistic videos of five actions (run, walk, jump, eat, drink) performed by different actors at different viewpoints to study the computational steps used to recognize actions across complex transformations. In particular, we ask when the brain discriminates between different actions, and when it does so in a manner that is invariant to changes in 3D viewpoint. We measure the latency difference between invariant and noninvariant action decoding when subjects view full videos as well as form-depleted and motion-depleted stimuli. We were unable to detect a difference in decoding latency or temporal profile between invariant and noninvariant action recognition in full videos. However, when either form or motion information is removed from the stimulus set, we observe a decrease and delay in invariant action decoding. Our results suggest that the brain recognizes actions and builds invariance to complex transformations at the same time and that both form and motion information are crucial for fast, invariant action recognition. NEW & NOTEWORTHY The human brain can quickly recognize actions despite transformations that change their visual appearance. We use neural timing data to uncover the computations underlying this ability. We find that within 200 ms action can be read out of magnetoencephalography data and that this representation is invariant to changes in viewpoint. We find form and motion are needed for this fast action decoding, suggesting that the brain quickly integrates complex spatiotemporal features to form invariant action representations.
2
Mc Laughlin, Myles, Joelle Nsimire Chabwine, Marcel van der Heijden, and Philip X. Joris. "Comparison of Bandwidths in the Inferior Colliculus and the Auditory Nerve. II: Measurement Using a Temporally Manipulated Stimulus." Journal of Neurophysiology 100, no. 4 (October 2008): 2312–27. http://dx.doi.org/10.1152/jn.90252.2008.
Full textAbstract:
To localize low-frequency sounds, humans rely on an interaural comparison of the temporally encoded sound waveform after peripheral filtering. This process can be compared with cross-correlation. For a broadband stimulus, after filtering, the correlation function has a damped oscillatory shape where the periodicity reflects the filter's center frequency and the damping reflects the bandwidth (BW). The physiological equivalent of the correlation function is the noise delay (ND) function, which is obtained from binaural cells by measuring response rate to broadband noise with varying interaural time delays (ITDs). For monaural neurons, delay functions are obtained by counting coincidences for varying delays across spike trains obtained to the same stimulus. Previously, we showed that BWs in monaural and binaural neurons were similar. However, earlier work showed that the damping of delay functions differs significantly between these two populations. Here, we address this paradox by looking at the role of sensitivity to changes in interaural correlation. We measured delay and correlation functions in the cat inferior colliculus (IC) and auditory nerve (AN). We find that, at a population level, AN and IC neurons with similar characteristic frequencies (CF) and BWs can have different responses to changes in correlation. Notably, binaural neurons often show compression, which is not found in the AN and which makes the shape of delay functions more invariant with CF at the level of the IC than at the AN. We conclude that binaural sensitivity is more dependent on correlation sensitivity than has hitherto been appreciated and that the mechanisms underlying correlation sensitivity should be addressed in future studies.
3
Watanabe, T., and K. Nagata. "Integral invariants and decay of temporally developing grid turbulence." Physics of Fluids 30, no. 10 (October 2018): 105111. http://dx.doi.org/10.1063/1.5045589.
Full text
4
Yang, Chengdong, Tingwen Huang, Kejia Yi, Ancai Zhang, Xiangyong Chen, Zhenxing Li, Jianlong Qiu, and Fuad E. Alsaadi. "Synchronization for Nonlinear Complex Spatio-Temporal Networks with Multiple Time-Invariant Delays and Multiple Time-Varying Delays." Neural Processing Letters 50, no. 2 (August 13, 2018): 1051–64. http://dx.doi.org/10.1007/s11063-018-9900-y.
Full text
5
NAKAZATO, HIROMICHI, MIKIO NAMIKI, and SAVERIO PASCAZIO. "TEMPORAL BEHAVIOR OF QUANTUM MECHANICAL SYSTEMS." International Journal of Modern Physics B 10, no. 03 (January 30, 1996): 247–95. http://dx.doi.org/10.1142/s0217979296000118.
Full textAbstract:
The temporal behavior of quantum mechanical systems is reviewed. We mainly focus our attention on the time development of the so-called “survival” probability of those systems that are initially prepared in eigenstates of the unperturbed Hamiltonian, by assuming that the latter has a continuous spectrum. The exponential decay of the survival probability, familiar, for example, in radioactive decay phenomena, is representative of a purely probabilistic character of the system under consideration and is naturally expected to lead to a master equation. This behavior, however, can be found only at intermediate times, for deviations from it exist both at short and long times and can have significant consequences. After a short introduction to the long history of the research on the temporal behavior of such quantum mechanical systems, the short-time behavior and its controversial consequences when it is combined with von Neumann’s projection postulate in quantum measurement theory are critically overviewed from a dynamical point of view. We also discuss the so-called quantum Zeno effect from this standpoint. The behavior of the survival amplitude is then scrutinized by investigating the analytic properties of its Fourier and Laplace transforms. The analytic property that there is no singularity except a branch cut running along the real energy axis in the first Riemannian sheet is an important reflection of the time-reversal invariance of the dynamics governing the whole process. It is shown that the exponential behavior is due to the presence of a simple pole in the second Riemannian sheet, while the contribution of the branch point yields a power behavior for the amplitude. The exponential decay form is cancelled at short times and dominated at very long times by the branch-point contributions, which give a Gaussian behavior for the former and a power behavior for the latter. In order to realize the exponential law in quantum theory, it is essential to take into account a certain kind of macroscopic nature of the total system, since the exponential behavior is regarded as a manifestation of a complete loss of coherence of the quantum subsystem under consideration. In this respect, a few attempts at extracting the exponential decay form on the basis of quantum theory, aiming at the master equation, are briefly reviewed, including van Hove’s pioneering work and his well-known “λ2T” limit. In the attempt to further clarify the mechanism of the appearance of a purely probabilistic behavior without resort to any approximation, a solvable dynamical model is presented and extensively studied. The model describes an ultrarelativistic particle interacting with N two-level systems (called “spins”) and is shown to exhibit an exponential behavior at all times in the weak-coupling, macroscopic limit. Furthermore, it is shown that the model can even reproduce the short-time Gaussian behavior followed by the exponential law when an appropriate initial state is chosen. The analysis is exact and no approximation is involved. An interpretation for the change of the temporal behavior in quantum systems is drawn from the results obtained. Some implications for the quantum measurement problem are also discussed, in particular in connection with dissipation.
6
LIN, CHIN-TENG, HSI-WEN NEIN, and WEN-CHIEH LIN. "A SPACE-TIME DELAY NEURAL NETWORK FOR MOTION RECOGNITION AND ITS APPLICATION TO LIPREADING." International Journal of Neural Systems 09, no. 04 (August 1999): 311–34. http://dx.doi.org/10.1142/s0129065799000319.
Full textAbstract:
Motion recognition has received increasing attention in recent years owing to heightened demand for computer vision in many domains, including the surveillance system, multimodal human computer interface, and traffic control system. Most conventional approaches classify the motion recognition task into partial feature extraction and time-domain recognition subtasks. However, the information of motion resides in the space-time domain instead of the time domain or space domain independently, implying that fusing the feature extraction and classification in the space and time domains into a single framework is preferred. Based on this notion, this work presents a novel Space-Time Delay Neural Network (STDNN) capable of handling the space-time dynamic information for motion recognition. The STDNN is unified structure, in which the low-level spatiotemporal feature extraction and high-level space-time-domain recognition are fused. The proposed network possesses the spatiotemporal shift-invariant recognition ability that is inherited from the time delay neural network (TDNN) and space displacement neural network (SDNN), where TDNN and SDNN are good at temporal and spatial shift-invariant recognition, respectively. In contrast to multilayer perceptron (MLP), TDNN, and SDNN, STDNN is constructed by vector-type nodes and matrix-type links such that the spatiotemporal information can be accurately represented in a neural network. Also evaluated herein is the performance of the proposed STDNN via two experiments. The moving Arabic numerals (MAN) experiment simulates the object's free movement in the space-time domain on image sequences. According to these results, STDNN possesses a good generalization ability with respect to the spatiotemporal shift-invariant recognition. In the lipreading experiment, STDNN recognizes the lip motions based on the inputs of real image sequences. This observation confirms that STDNN yields a better performance than the existing TDNN-based system, particularly in terms of the generalization ability. In addition to the lipreading application, the STDNN can be applied to other problems since no domain-dependent knowledge is used in the experiment.
7
Creutzig, Felix, Jan Benda, Sandra Wohlgemuth, Andreas Stumpner, Bernhard Ronacher, and Andreas V. M. Herz. "Timescale-Invariant Pattern Recognition by Feedforward Inhibition and Parallel Signal Processing." Neural Computation 22, no. 6 (June 2010): 1493–510. http://dx.doi.org/10.1162/neco.2010.05-09-1016.
Full textAbstract:
The timescale-invariant recognition of temporal stimulus sequences is vital for many species and poses a challenge for their sensory systems. Here we present a simple mechanistic model to address this computational task, based on recent observations in insects that use rhythmic acoustic communication signals for mate finding. In the model framework, feedforward inhibition leads to burst-like response patterns in one neuron of the circuit. Integrating these responses over a fixed time window by a readout neuron creates a timescale-invariant stimulus representation. Only two additional processing channels, each with a feature detector and a readout neuron, plus one final coincidence detector for all three parallel signal streams, are needed to account for the behavioral data. In contrast to previous solutions to the general time-warp problem, no time delay lines or sophisticated neural architectures are required. Our results suggest a new computational role for feedforward inhibition and underscore the power of parallel signal processing.
8
Musgrove, Frank W. "Time‐variant statics corrections during interpretation." GEOPHYSICS 59, no. 3 (March 1994): 474–83. http://dx.doi.org/10.1190/1.1443609.
Full textAbstract:
Even though statics processing is well advanced and is routinely applied, interpreters are still required to evaluate seismic data that has either no statics corrections or poor statics corrections. It is a critical interpretation skill to recognize uncorrected statics and to correct for their effects. Poor decisions and dry holes are often the result of failure to do this. Since multifold seismic data has become the norm, statics are no longer time invariant. The method of flattening stacked data on a shallow reflector that worked so well for single fold data will show anomalous structure and isochron variation caused by the time‐variant effects of uncorrected statics. Uncorrected statics can be identified by anomalous undulations in a shallow reflector, by the time‐variant effects with increasing reflection time, and by the variations in optimal stacking velocities, all of which have been documented in the literature. Knowledge of these properties from stacked data observations can lead to robust estimates of the surface position delay profile necessary for all statics corrections. Although prestack analysis and correction provide the best solutions, full spatial and temporal corrections can be calculated easily and applied to the interpretation of stacked data on most work stations to enable quicker, less expensive decision making. Prestack reprocessing is only one action that may result from a quality poststack analysis. Stacked data time picks can be fully corrected with a statics term and a velocity term. Partial corrections, applied only to the center trace of a static‐causing body can be made without knowledge of the exact surface position delay model. The ratio of central trace delays of two reflectors is approximately equal to the ratio of effective spread lengths used to stack the two reflectors. This method is applied to a real data example published last year in Geophysics where the anomalous isochron thinning is accurately predicted.
9
Mutel, R. L., D. A. Gurnett, and I. W. Christopher. "Spatial and temporal properties of AKR burst emission derived from Cluster WBD VLBI studies." Annales Geophysicae 22, no. 7 (July 14, 2004): 2625–32. http://dx.doi.org/10.5194/angeo-22-2625-2004.
Full textAbstract:
Abstract. We have determined the locations of over 6000 individual auroral kilometric radiation (AKR) bursts between July 2002 and May 2003 using a very long baseline interferometer (VLBI) array. Burst locations were determined by triangulation using differential delays from cross-correlated Cluster WBD waveforms. Typical position uncertainties are 200-400km in the plane normal to the source-spacecraft line, but much larger along this line. The AKR bursts are generally located above the auroral zone with a strong preference for the evening sector (22:00 MLT±2h). However, a few epochs imaged during the austral summer have loci in the daytime sector, especially near 15:00 MLT. There is marginal evidence for a small N-S hemispheric asymmetry in mean MLT and invariant latitude.
10
Lainscsek, Claudia, Jonathan Weyhenmeyer, Sydney S. Cash, and Terrence J. Sejnowski. "Delay Differential Analysis of Seizures in Multichannel Electrocorticography Data." Neural Computation 29, no. 12 (December 2017): 3181–218. http://dx.doi.org/10.1162/neco_a_01009.
Full textAbstract:
High-density electrocorticogram (ECoG) electrodes are capable of recording neurophysiological data with high temporal resolution with wide spatial coverage. These recordings are a window to understanding how the human brain processes information and subsequently behaves in healthy and pathologic states. Here, we describe and implement delay differential analysis (DDA) for the characterization of ECoG data obtained from human patients with intractable epilepsy. DDA is a time-domain analysis framework based on embedding theory in nonlinear dynamics that reveals the nonlinear invariant properties of an unknown dynamical system. The DDA embedding serves as a low-dimensional nonlinear dynamical basis onto which the data are mapped. This greatly reduces the risk of overfitting and improves the method's ability to fit classes of data. Since the basis is built on the dynamical structure of the data, preprocessing of the data (e.g., filtering) is not necessary. We performed a large-scale search for a DDA model that best fit ECoG recordings using a genetic algorithm to qualitatively discriminate between different cortical states and epileptic events for a set of 13 patients. A single DDA model with only three polynomial terms was identified. Singular value decomposition across the feature space of the model revealed both global and local dynamics that could differentiate electrographic and electroclinical seizures and provided insights into highly localized seizure onsets and diffuse seizure terminations. Other common ECoG features such as interictal periods, artifacts, and exogenous stimuli were also analyzed with DDA. This novel framework for signal processing of seizure information demonstrates an ability to reveal unique characteristics of the underlying dynamics of the seizure and may be useful in better understanding, detecting, and maybe even predicting seizures.
11
Stange-Marten, Annette, Alisha L. Nabel, James L. Sinclair, Matthew Fischl, Olga Alexandrova, Hilde Wohlfrom, Conny Kopp-Scheinpflug, Michael Pecka, and Benedikt Grothe. "Input timing for spatial processing is precisely tuned via constant synaptic delays and myelination patterns in the auditory brainstem." Proceedings of the National Academy of Sciences 114, no. 24 (May 30, 2017): E4851—E4858. http://dx.doi.org/10.1073/pnas.1702290114.
Full textAbstract:
Precise timing of synaptic inputs is a fundamental principle of neural circuit processing. The temporal precision of postsynaptic input integration is known to vary with the computational requirements of a circuit, yet how the timing of action potentials is tuned presynaptically to match these processing demands is not well understood. In particular, action potential timing is shaped by the axonal conduction velocity and the duration of synaptic transmission delays within a pathway. However, it is not known to what extent these factors are adapted to the functional constraints of the respective circuit. Here, we report the finding of activity-invariant synaptic transmission delays as a functional adaptation for input timing adjustment in a brainstem sound localization circuit. We compared axonal and synaptic properties of the same pathway between two species with dissimilar timing requirements (gerbil and mouse): In gerbils (like humans), neuronal processing of sound source location requires exceptionally high input precision in the range of microseconds, but not in mice. Activity-invariant synaptic transmission and conduction delays were present exclusively in fast conducting axons of gerbils that also exhibited unusual structural adaptations in axon myelination for increased conduction velocity. In contrast, synaptic transmission delays in mice varied depending on activity levels, and axonal myelination and conduction velocity exhibited no adaptations. Thus, the specializations in gerbils and their absence in mice suggest an optimization of axonal and synaptic properties to the specific demands of sound localization. These findings significantly advance our understanding of structural and functional adaptations for circuit processing.
12
Levinton, Jeffrey S., and James S. Farris. "On the estimation of taxonomic longevity from Lyellian curves." Paleobiology 13, no. 4 (1987): 479–83. http://dx.doi.org/10.1017/s0094837300009052.
Full textAbstract:
Stanley's (1979) method of estimating taxonomic longevity from Lyellian curves differs from Kurtén's (1960) because of different underlying assumptions. Kurtén's model supposes that taxon richness and longevity are stochastically invariate over the period used for the Lyellian estimate. Both Kurtén and Stanley seek to calculate the average longevity of a taxon, when the temporal stratigraphic ranges are known after and before a given time datum. Under the exponential decay model used by Kurtén, mean taxonomic longevity is indeed approximately 2.89 half-lives, as he maintained. Stanley's estimate is based on the unrealistic assumptions of uniform longevity and evenly-spaced origins of fossil taxa. This leads to an estimate of longevity as exactly two half-lives.
13
Schafaschek, Germano, Laurent Hardouin, and Jörg Raisch. "Optimal control of timed event graphs with resource sharing and output-reference update." at - Automatisierungstechnik 68, no. 7 (July 26, 2020): 512–28. http://dx.doi.org/10.1515/auto-2020-0051.
Full textAbstract:
AbstractTimed event graphs (TEGs) are a subclass of timed Petri nets that model synchronization and delay phenomena, but not conflict or choice. We consider a scenario where a number of TEGs share one or several resources and are subject to changes in their output-reference signals. Because of resource sharing, the resulting overall discrete event system is not a TEG. We propose a formal method to determine the optimal control input for such systems, where optimality is in the sense of the widely adopted just-in-time criterion. Our approach is based on a prespecified priority policy for the TEG components of the overall system. It builds on existing control theory for TEGs, which exploits the fact that, in a suitable mathematical framework (idempotent semirings such as the max-plus or the min-plus algebra), the temporal evolution of TEGs can be described by a set of linear time-invariant equations.
14
Endriz, John, Peggy P. Ho, and Lawrence Steinman. "Time correlation between mononucleosis and initial symptoms of MS." Neurology - Neuroimmunology Neuroinflammation 4, no. 3 (February 27, 2017): e308. http://dx.doi.org/10.1212/nxi.0000000000000308.
Full textAbstract:
Objective:To determine the average age of MS onset vs the age at which Epstein-Barr infection has previously occurred and stratify this analysis by sex and the blood level of Epstein-Barr nuclear antigen 1 (EBNA1) antibody.Methods:Using infectious mononucleosis (IM) as a temporal marker in data from the Swedish epidemiologic investigation of MS, 259 adult IM/MS cases were identified and then augmented to account for “missing” childhood data so that the average age of MS onset could be determined for cases binned by age of IM (as stratified by sex and EBNA1 titer level).Results:Mean age of IM vs mean age of MS reveals a positive time correlation for all IM ages (from ∼5 to ∼30 years), with IM-to-MS delay decreasing with increased age. When bifurcated by sex or EBNA1 blood titer levels, males and high-titer subpopulations show even stronger positive time correlation, while females and low-titer populations show negative time correlation in early childhood (long IM/MS delay). The correlation becomes positive in females beyond puberty.Conclusions:IM/MS time correlation implies causality if IM is time random. Alternative confounding models seem implausible, in light of constraints imposed by time-invariant delay observed here. Childhood infection with Epstein-Barr virus (EBV) in females and/or those genetically prone to low EBNA1 blood titers will develop MS slowly. Males and/or high EBNA1-prone develop MS more rapidly following IM infection at all ages. For all, postpubescent EBV infection is critical for the initiation and rapid development of MS.
15
Aslanov, Rasim B., Leman M. Dashdemirova, Oktay Z. Alekperov, Azad R. Abdurahimov, and Oktay K. Gasymov. "Dynamics of Proteins by Thermal Decay of Free Radicals Induced by Ultraviolet Irradiation." Journal of Spectroscopy 2018 (June 28, 2018): 1–6. http://dx.doi.org/10.1155/2018/6197636.
Full textAbstract:
The relationship between structure, dynamics, and function of biomolecules is a fundamental interest of biophysics. Protein dynamics drastically vary in temporal and spatial scales. The function of a particular protein determines the significance of a distinct type of dynamics. Here, we investigate the influence of hydration water on the dynamics of a protein called silk fibroin. Particular interest is to investigate the protein dynamics using thermal decay of the free radicals induced by ultraviolet irradiation. The full decay of the free radicals occurs at very wide temperature region (120 K–340 K). Three distinct regions with transition points of ∼135 K, 205 K, and 279 K are apparent in the thermal decay curves of hydrated fibroin samples. The first transition (∼135 K) that leads 2–6% increase of total spins was observed only in the decay curves of fibroin submerged in 40% and 50% glycerol. The second transition (∼205 K) was invariant for all samples, hydrated and dry fibroins. The third transition of 279 K common for all hydrated fibroin samples was shifted about 84 K to a higher temperature of 363 K in dry fibroin. The thermal transitions at 205 K and 279 K are weakly and strongly, respectively, coupled to water molecules. Nature of the free radicals participated in these transitions was identified. The significance of the findings for protein dynamics is discussed.
16
Drew, Patrick J., and L. F. Abbott. "Models and Properties of Power-Law Adaptation in Neural Systems." Journal of Neurophysiology 96, no. 2 (August 2006): 826–33. http://dx.doi.org/10.1152/jn.00134.2006.
Full textAbstract:
Many biological systems exhibit complex temporal behavior that cannot be adequately characterized by a single time constant. This dynamics, observed from single channels up to the level of human psychophysics, is often better described by power-law rather than exponential dependences on time. We develop and study the properties of neural models with scale-invariant, power-law adaptation and contrast them with the more commonly studied exponential case. Responses of an adapting firing-rate model to constant, pulsed, and oscillating inputs in both the power-law and exponential cases are considered. We construct a spiking model with power-law adaptation based on a nested cascade of processes and show that it can be “programmed” to produce a wide range of time delays. Finally, within a network model, we use power-law adaptation to reproduce long-term features of the tilt aftereffect.
17
Muehlen, Iris, Stephan P. Kloska, Philipp Gölitz, Philip Hölter, Lorenz Breuer, Hendrik Ditt, and Arnd Doerfler. "Noninvasive Collateral Flow Velocity Imaging in Acute Ischemic Stroke: Intraindividual Comparison of 4D-CT Angiography with Digital Subtraction Angiography." RöFo - Fortschritte auf dem Gebiet der Röntgenstrahlen und der bildgebenden Verfahren 191, no. 09 (January 21, 2019): 827–35. http://dx.doi.org/10.1055/a-0825-6660.
Full textAbstract:
Purpose The collateral status can be defined not only by its morphological extent but also by the velocity of collateral filling characterized by the relative filling time delay (rFTD). The aim of our study was to compare different methods of noninvasive visualization of rFTD derived from 4D-CT angiography (4D-CTA) with digital substraction angiography (DSA) and to investigate the correlation between functional and morphological collateral status on timing-invariant CTA. Materials and Methods 50 consecutive patients with acute occlusion in the M1 segment who underwent DSA for subsequent mechanical recanalization after multimodal CT were retrospectively analyzed. 4D-CTA data were used to assess the relative filling time delay between the A1 segment of the affected hemisphere and the sylvian branches distal to the occluded M1 segment using source images (4D-CTA-SI) and color-coded flow velocity visualization with prototype software (fv-CTA) in comparison to DSA. The morphological extent of collaterals was assessed on the basis of the Collateral Score (CS) on temporal maximum intensity projections (tMIP) derived from CT perfusion data. Results There was very good correlation of rFTD between fv-CTA and DSA (n = 50, r = 0.9, p < 0.05). Differences of absolute rFTD values were not significant. 4D-CTA-SI and DSA also showed good correlation (n = 50, r = 0.6, p < 0.05), but mean values of rFTD were significantly different (p < 0.05). rFTD derived from fvCTA and CS derived from timing-invariant CTA showed a negative association (R = – 0.5; P = 0.000). In patients with a favorable radiological outcome defined by a TICI score of 2b or 3, there was a significant negative correlation of CS and mRS at 3 months (R = – 0.4, P = 0.006). Conclusion Collateral status plays an important role in the outcome in stroke patients. rFTD derived from 4D-CTA is a suitable parameter for noninvasive imaging of collateral velocity, which correlates with the morphological extent of collaterals. Further studies are needed to define valid thresholds for rFTD and to evaluate the diagnostic and prognostic value. Key points: Citation Format
18
Mlotshwa, Mandla, Catherine Riou, Denis Chopera, Debra de Assis Rosa, Roman Ntale, Florette Treunicht, Zenda Woodman, et al. "Fluidity of HIV-1-Specific T-Cell Responses during Acute and Early Subtype C HIV-1 Infection and Associations with Early Disease Progression." Journal of Virology 84, no. 22 (September 8, 2010): 12018–29. http://dx.doi.org/10.1128/jvi.01472-10.
Full textAbstract:
ABSTRACT Deciphering immune events during early stages of human immunodeficiency virus type 1 (HIV-1) infection is critical for understanding the course of disease. We characterized the hierarchy of HIV-1-specific T-cell gamma interferon (IFN-γ) enzyme-linked immunospot (ELISPOT) assay responses during acute subtype C infection in 53 individuals and associated temporal patterns of responses with disease progression in the first 12 months. There was a diverse pattern of T-cell recognition across the proteome, with the recognition of Nef being immunodominant as early as 3 weeks postinfection. Over the first 6 months, we found that there was a 23% chance of an increased response to Nef for every week postinfection (P = 0.0024), followed by a nonsignificant increase to Pol (4.6%) and Gag (3.2%). Responses to Env and regulatory proteins appeared to remain stable. Three temporal patterns of HIV-specific T-cell responses could be distinguished: persistent, lost, or new. The proportion of persistent T-cell responses was significantly lower (P = 0.0037) in individuals defined as rapid progressors than in those progressing slowly and who controlled viremia. Almost 90% of lost T-cell responses were coincidental with autologous viral epitope escape. Regression analysis between the time to fixed viral escape and lost T-cell responses (r = 0.61; P = 0.019) showed a mean delay of 14 weeks after viral escape. Collectively, T-cell epitope recognition is not a static event, and temporal patterns of IFN-γ-based responses exist. This is due partly to viral sequence variation but also to the recognition of invariant viral epitopes that leads to waves of persistent T-cell immunity, which appears to associate with slower disease progression in the first year of infection.
19
Norris, Brian J., Adam L. Weaver, Angela Wenning, Paul S. García, and Ronald L. Calabrese. "A Central Pattern Generator Producing Alternative Outputs: Pattern, Strength, and Dynamics of Premotor Synaptic Input to Leech Heart Motor Neurons." Journal of Neurophysiology 98, no. 5 (November 2007): 2992–3005. http://dx.doi.org/10.1152/jn.00877.2007.
Full textAbstract:
The central pattern generator (CPG) for heartbeat in medicinal leeches consists of seven identified pairs of segmental heart interneurons and one unidentified pair. Four of the identified pairs and the unidentified pair of interneurons make inhibitory synaptic connections with segmental heart motor neurons. The CPG produces a side-to-side asymmetric pattern of intersegmental coordination among ipsilateral premotor interneurons corresponding to a similarly asymmetric fictive motor pattern in heart motor neurons, and asymmetric constriction pattern of the two tubular hearts, synchronous and peristaltic. Using extracellular recordings from premotor interneurons and voltage-clamp recordings of ipsilateral segmental motor neurons in 69 isolated nerve cords, we assessed the strength and dynamics of premotor inhibitory synaptic output onto the entire ensemble of heart motor neurons and the associated conduction delays in both coordination modes. We conclude that premotor interneurons establish a stereotypical pattern of intersegmental synaptic connectivity, strengths, and dynamics that is invariant across coordination modes, despite wide variations among preparations. These data coupled with a previous description of the temporal pattern of premotor interneuron activity and relative phasing of motor neuron activity in the two coordination modes enable a direct assessment of how premotor interneurons through their temporal pattern of activity and their spatial pattern of synaptic connectivity, strengths, and dynamics coordinate segmental motor neurons into a functional pattern of activity.
20
Tiburzi, C., G. M. Shaifullah, C. G. Bassa, P. Zucca, J. P. W. Verbiest, N. K. Porayko, E. van der Wateren, et al. "The impact of solar wind variability on pulsar timing." Astronomy & Astrophysics 647 (March 2021): A84. http://dx.doi.org/10.1051/0004-6361/202039846.
Full textAbstract:
Context. High-precision pulsar timing requires accurate corrections for dispersive delays of radio waves, parametrized by the dispersion measure (DM), particularly if these delays are variable in time. In a previous paper, we studied the solar wind (SW) models used in pulsar timing to mitigate the excess of DM that is annually induced by the SW and found these to be insufficient for high-precision pulsar timing. Here we analyze additional pulsar datasets to further investigate which aspects of the SW models currently used in pulsar timing can be readily improved, and at what levels of timing precision SW mitigation is possible. Aims. Our goals are to verify: (a) whether the data are better described by a spherical model of the SW with a time-variable amplitude, rather than a time-invariant one as suggested in literature, and (b) whether a temporal trend of such a model’s amplitudes can be detected. Methods. We use the pulsar timing technique on low-frequency pulsar observations to estimate the DM and quantify how this value changes as the Earth moves around the Sun. Specifically, we monitor the DM in weekly to monthly observations of 14 pulsars taken with parts of the LOw-Frequency ARray (LOFAR) across time spans of up to 6 years. We develop an informed algorithm to separate the interstellar variations in the DM from those caused by the SW and demonstrate the functionality of this algorithm with extensive simulations. Assuming a spherically symmetric model for the SW density, we derive the amplitude of this model for each year of observations. Results. We show that a spherical model with a time-variable amplitude models the observations better than a spherical model with a constant amplitude, but that both approaches leave significant SW-induced delays uncorrected in a number of pulsars in the sample. The amplitude of the spherical model is found to be variable in time, as opposed to what has been previously suggested.
21
Wijsen, N., A. Aran, B. Sanahuja, J. Pomoell, and S. Poedts. "The effect of drifts on the decay phase of SEP events." Astronomy & Astrophysics 634 (February 2020): A82. http://dx.doi.org/10.1051/0004-6361/201937026.
Full textAbstract:
Aims. We study the effect of the magnetic gradient and curvature drifts on the pitch-angle dependent transport of solar energetic particles (SEPs) in the heliosphere, focussing on ∼3–36 MeV protons. By considering observers located at different positions in the heliosphere, we investigate how drifts may alter the measured intensity-time profiles and energy spectra. We focus on the decay phase of solar energetic proton events in which a temporal invariant spectrum and disappearing spatial intensity gradients are often observed; a phenomenon known as the “reservoir effect” or the “SEP flood”. We study the effects of drifts by propagating particles both in nominal and non-nominal solar wind conditions. Methods. We used a three-dimensional (3D) particle transport model, solving the focused transport equation extended with the effect of particle drifts in the spatial term. Nominal Parker solar wind configurations of different speeds and a magnetohydrodynamic (MHD) generated solar wind containing a corotating interaction region (CIR) were considered. The latter configuration gives rise to a magnetic bottle structure, with one bottleneck at the Sun and the other at the CIR. We inject protons from a fixed source at 0.1 AU, the inner boundary of the MHD model. Results. When the drift induced particle net-flux is zero, the modelled intensity-time profiles obtained at different radial distances along an IMF line show the same intensity fall-off after the prompt phase of the particle event, which is in accordance with the SEP flood phenomenon. However, observers magnetically connected close to the edges of the particle injection site can experience, as a result of drifts, a sudden drop in the intensities occurring at different times for different energies such that no SEP flood phenomenon is established. In the magnetic bottle structure, this effect is enhanced due to the presence of magnetic field gradients strengthening the nominal particle drifts. Moreover, anisotropies can be large for observers that only receive particles through drifts, illustrating the importance of pitch-angle dependent 3D particle modelling. We observe that interplanetary cross-field diffusion can mitigate the effects of particle drifts. Conclusions. Particle drifts can substantially modify the decay phase of SEP events, especially if the solar wind contains compression regions or shock waves where the drifts are enhanced. This is, for example, the case for our CIR solar wind configuration generated with a 3D MHD model, where the effect of drifts is strong. A similar decay rate in different energy channels and for different observers requires the mitigation of the effect of drifts. One way to accomplish this is through interplanetary cross-field diffusion, suggesting thus a way to determine a minimum value for the cross-field diffusion strength.
22
Yongsheng, Li, Tian Yunfeng, Yu Chen, Su Zhe, Jiang Wenliang, Li Zhenhong, Zhang Jingfa, Luo Yi, and Li Bingquan. "Present-day interseismic deformation characteristics of the Beng Co-Dongqiao conjugate fault system in central Tibet: implications from InSAR observations." Geophysical Journal International 221, no. 1 (January 8, 2020): 492–503. http://dx.doi.org/10.1093/gji/ggaa014.
Full textAbstract:
SUMMARY Numerous V-shaped conjugate strike-slip fault systems distributed between the Lhasa block and the Qiangtang block serve as some of the main structures accommodating the eastward motion of the Tibetan Plateau. The Beng Co-Dongqiao conjugate fault system is a representative section, and determining its tectonic environment is a fundamental issue for understanding the dynamic mechanism of the V-shaped conjugate strike-slip fault systems throughout central Tibet. In this paper, we investigate the deformation rates of the Beng Co-Dongqiao conjugate faults using 3 yr of SAR data from both ascending and descending tracks of Sentinel-1 satellites. Only interferograms with a long temporal baseline were used to increase the proportion of the deformation signals. The external atmospheric delay product and the InSAR stacking strategy were employed to reduce various errors in the large-spatial-coverage Sentinel-1 data. The InSAR results revealed that the fault-parallel deformation velocities along the eastern and western segments of the Beng Co fault are 5 ± 1 mm/yr and 2.5 ± 1 mm/yr, respectively. The second invariant of the horizontal strain rates shows that the accumulated strain is centered on the eastern segment of the Beng Co Fault and Gulu rift. The velocity and strain rate fields show that the Anduo-Peng Co faults may be paired with the Beng Co fault to form a new conjugate system and the tectonic transformation between the Beng Co fault and Gulu rift. These results can better explain the tectonic deformation environment of the Beng Co-Dongqiao conjugate fault system and provide insights on the crustal dynamics throughout the entire plateau interior.
23
Snyder, L. H., and W. M. King. "Effect of viewing distance and location of the axis of head rotation on the monkey's vestibuloocular reflex. I. Eye movement responses." Journal of Neurophysiology 67, no. 4 (April 1, 1992): 861–74. http://dx.doi.org/10.1152/jn.1992.67.4.861.
Full textAbstract:
1. The vestibuloocular reflex (VOR) stabilizes images on the retina against movements of the head in space. Viewing distance, target eccentricity, and location of the axis of rotation may influence VOR responses because rotation of the head about most axes in space rotates and translates the eyes relative to visual targets. To study the VOR response to combined rotation and translation, monkeys were placed on a rate table and rotated briefly in the dark about a vertical axis that was located in front of or behind the eyes. The monkeys fixated a near or far visual target that was extinguished before the rotation. Eye movements were recorded from both eyes by the use of the search coil technique. 2. Peak eye velocity evoked by the VOR was linearly related to vergence angle for any axis of rotation. The percent change in the VOR with near target viewing relative to far target viewing at a vergence angle of 20 degrees was linearly related to the location of the axis of rotation. Axes located behind the eyes produced positive changes in VOR amplitude, and axes located in front of the eyes produced negative changes in VOR amplitude. An axis of rotation located in the coronal plane containing the centers of rotation of the eyes produced no modification of VOR amplitude. For any axis, the VOR compensated for approximately 90% of the translation of the eye relative to near targets. 3. The initial VOR response was not correct in magnitude but was refined by a series of three temporally delayed corrections of increasing complexity. The earliest VOR-evoked eye movement (10-20 ms after rotation onset) was independent of viewing distance and rotational axis location. In the next 100 ms, eye speed appeared to be sequentially modified three times: within 20 ms by viewing distance; within 30 ms by otolith translation; and within 100 ms by eye translation relative to the visual target. 4. These data suggest a formal model of the VOR consisting of four channels. Channel 1 conveys an unmodified head rotation signal with a pure delay of 10 ms. Channel 2 conveys an angular head velocity signal, modified by viewing distance with a pure delay of 20 ms, but invariant with respect to the location of the axis of rotation. Channel 3 conveys a linear head velocity signal, dependent on the location of the axis of rotation, that is modified by viewing distance with a pure delay of 30 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
24
Handcock, Mark S., and Marilyn N. Raphael. "Modeling the annual cycle of daily Antarctic sea ice extent." Cryosphere 14, no. 7 (July 2, 2020): 2159–72. http://dx.doi.org/10.5194/tc-14-2159-2020.
Full textAbstract:
Abstract. The total Antarctic sea ice extent (SIE) experiences a distinct annual cycle, peaking in September and reaching its minimum in February. In this paper we propose a mathematical and statistical decomposition of this temporal variation in SIE. Each component is interpretable and, when combined, gives a complete picture of the variation in the sea ice. We consider timescales varying from the instantaneous and not previously defined to the multi-decadal curvilinear trend, the longest. Because our representation is daily, these timescales of variability give precise information about the timing and rates of advance and retreat of the ice and may be used to diagnose physical contributors to variability in the sea ice. We define a number of annual cycles each capturing different components of variation, especially the yearly amplitude and phase that are major contributors to SIE variation. Using daily sea ice concentration data, we show that our proposed invariant annual cycle explains 29 % more of the variation in daily SIE than the traditional method. The proposed annual cycle that incorporates amplitude and phase variation explains 77 % more variation than the traditional method. The variation in phase explains more of the variability in SIE than the amplitude. Using our methodology, we show that the anomalous decay of sea ice in 2016 was associated largely with a change of phase rather than amplitude. We show that the long term trend in Antarctic sea ice extent is strongly curvilinear and the reported positive linear trend is small and dependent strongly on a positive trend that began around 2011 and continued until 2016.
25
Lombardi, Aniello, Peter Jedlicka, Heiko J. Luhmann, and Werner Kilb. "Coincident glutamatergic depolarizations enhance GABAA receptor-dependent Cl- influx in mature and suppress Cl- efflux in immature neurons." PLOS Computational Biology 17, no. 1 (January 19, 2021): e1008573. http://dx.doi.org/10.1371/journal.pcbi.1008573.
Full textAbstract:
The impact of GABAergic transmission on neuronal excitability depends on the Cl--gradient across membranes. However, the Cl--fluxes through GABAA receptors alter the intracellular Cl- concentration ([Cl-]i) and in turn attenuate GABAergic responses, a process termed ionic plasticity. Recently it has been shown that coincident glutamatergic inputs significantly affect ionic plasticity. Yet how the [Cl-]i changes depend on the properties of glutamatergic inputs and their spatiotemporal relation to GABAergic stimuli is unknown. To investigate this issue, we used compartmental biophysical models of Cl- dynamics simulating either a simple ball-and-stick topology or a reconstructed CA3 neuron. These computational experiments demonstrated that glutamatergic co-stimulation enhances GABA receptor-mediated Cl- influx at low and attenuates or reverses the Cl- efflux at high initial [Cl-]i. The size of glutamatergic influence on GABAergic Cl--fluxes depends on the conductance, decay kinetics, and localization of glutamatergic inputs. Surprisingly, the glutamatergic shift in GABAergic Cl--fluxes is invariant to latencies between GABAergic and glutamatergic inputs over a substantial interval. In agreement with experimental data, simulations in a reconstructed CA3 pyramidal neuron with physiological patterns of correlated activity revealed that coincident glutamatergic synaptic inputs contribute significantly to the activity-dependent [Cl-]i changes. Whereas the influence of spatial correlation between distributed glutamatergic and GABAergic inputs was negligible, their temporal correlation played a significant role. In summary, our results demonstrate that glutamatergic co-stimulation had a substantial impact on ionic plasticity of GABAergic responses, enhancing the attenuation of GABAergic inhibition in the mature nervous systems, but suppressing GABAergic [Cl-]i changes in the immature brain. Therefore, glutamatergic shift in GABAergic Cl--fluxes should be considered as a relevant factor of short-term plasticity.
26
Maex, R., and G. A. Orban. "Model circuit of spiking neurons generating directional selectivity in simple cells." Journal of Neurophysiology 75, no. 4 (April 1, 1996): 1515–45. http://dx.doi.org/10.1152/jn.1996.75.4.1515.
Full textAbstract:
1. We here consider the property of directional selectivity (DS) in simple cells of layer 4 of cat area 17 as an instance of a receptive field (RF) transformation between two monosynaptically connected neuron populations: the afferent geniculate (lateral geniculate nucleus, LGN) cells and their target, layer 4 simple cells. We have studied this particular RF transformation because the large set of experimental data available allowed us to restrain the synaptic organization of our model layer 4 circuitry. 2. The one-compartment, spiking model neurons of the layer 4 circuitry are excitatory (adapting) or inhibitory (nonadapting). They all have simple-cell RFs composed of two spatially separated ON and OFF subregions. The sequence of the subregions across the neurons' RFs, which is determined by the geniculocortical inputs they receive, varies independently from their preferred direction of stimulus motion, which is determined by spatial asymmetries in their corticocortical inputs. 3. Synaptic transmission in the model layer 4 circuitry is mediated via non-N-methyl-D-aspartate (non-NMDA) receptors (geniculocortical excitation), via NMDA receptors (corticocortical excitation), and via gamma-aminobutyric acid-A receptors (corticocortical inhibition). Excitatory and inhibitory cortical neurons receive the same afferents. However, excitatory neurons form efferent synapses exclusively with neurons having the same RF characteristics, and preferentially with those having the same RF position. Inhibitory neurons form synapses preferentially with neurons having different RF characteristics or adjacent RF positions. 4. By comparing the neurons' numerically computed responses to visual stimuli with those of actual simple cells, the topology of the corticocortical connections has been constrained. The experimental responses to stationary and moving, and to bar as well as grating, stimuli are consistently reproduced with a single constant parameter setting. 5. Subsequently, the model has been analyzed from a system-theoretic approach and has been manipulated in order to find the components critical for its proper functioning. Variations on the model have been simulated for evaluating the performance of alternative connection schemes. 6. Spatially opponent inhibition between model simple cells with antagonistic RF subregions is necessary for the restoration of linearity lost at the LGN output. It hyperpolarizes model simple cells when the contrast polarity of an efficient stimulus is reversed and prevents, particularly in directionally nonselective cells, a frequency doubling of the responses to sine wave gratings of low spatial frequencies. 7. Directionally opponent inhibition between model simple cells preferring opposite directions of motion is necessary for the generation of genuine DS (a ratio of firing rates > 2 for opposite directions of motion). 8. The corticocortical excitatory polysynaptic feedback loops in the model are able to provide the time delays needed to generate DS, and even to preserve DS at very low speeds. The strength spatial extension, and time course of this corticocortical feedback excitation, together with the dynamics of the geniculate afferents and the width of the RF, determine the tuning of model simple cells in the temporal and velocity domain. 9. The present model generates directionally selective responses to stimulus motion over distances smaller than the width of a single subregion and as small as the spacing between the afferent geniculate RFs. The direction-selective mechanism acts uniformly across the entire width of a subregion. Thus the position invariance of DS arises in the present model at the same level as DS itself. The same holds for the stimulus polarity (light vs. dark) invariance of DS. Consequently, there is no need for highly hierarchical models in which all these characteristics accumulate in simple cells by pooling from lower-order subunits or neurons.
27
Koshland, G. F., and J. L. Smith. "Mutable and immutable features of paw-shake responses after hindlimb deafferentation in the cat." Journal of Neurophysiology 62, no. 1 (July 1, 1989): 162–73. http://dx.doi.org/10.1152/jn.1989.62.1.162.
Full textAbstract:
1. Hindlimb paw-shake responses were assessed before and after unilateral deafferentation (L3-S1) in chronic-spinal cats (n = 5), spinalized at the T12 level 1 yr earlier. Selected ankle flexor [tibialis anterior (TA)] and extensor [lateral gastrocnemius (LG)] and knee extensor [vastus lateralis (VL)] muscles were surgically implanted with chronic electromyographic (EMG) electrodes to determine mutable features of cycle characteristics and muscle synergies that are modulated by motion-dependent feedback as opposed to immutable features that are centrally programmed and not modulated by limb afference. 2. Paw-shake responses were difficult to elicit in the extensively deafferented hindlimb; this was true particularly during the first recovery weeks after deafferentation. By the end of the first month, however, brief responses of 1 or 2 cycles were commonly elicited in four of five cats, and responses of 3-7 cycles were common by the end of the second month in three of five cats. Initially, responses in the deafferented limb were elicited by stimuli applied to the dorsolateral thigh, an oval patch of skin innervated by intact S2 afferents. Over the 4-mo recovery period, however, the receptive field of the largely denervated skin expanded, and responses were also elicited by stimuli applied to the lateral aspect of the knee and shank, but usually not the paw. 3. In addition to fewer average cycles per response (5 vs. 10 cycles), paw shaking evoked in the deafferented hindlimb was characterized by longer-than-average cycle periods (124 vs. 98 ms), but the average cycle period varied widely among responses, ranging from 99 to 239 ms. Before deafferentation, the temporal organization of consecutive cycles was stereotypic; cycle periods increased linearly throughout a response. After deafferentation, however, there was no systematic relationship between cycle period and cycle number, and approximately 14% of the records with greater than or equal to 3 cycles were characterized by arhythmical sequences of EMG bursts. 4. At the ankle, LG burst duration was not altered by deafferentation, but TA onset and burst duration were affected. Before deafferentation, TA onset was invariant with respect to the beginning of the cycle, and burst duration increased linearly with cycle period. After deafferentation, however, TA onset was delayed, and the delay increased linearly with cycle period. Consequently, the TA burst duration was brief and unrelated to cycle period.(ABSTRACT TRUNCATED AT 400 WORDS)
28
Dürr, Volker, and Martin Egelhaaf. "In Vivo Calcium Accumulation in Presynaptic and Postsynaptic Dendrites of Visual Interneurons." Journal of Neurophysiology 82, no. 6 (December 1, 1999): 3327–38. http://dx.doi.org/10.1152/jn.1999.82.6.3327.
Full textAbstract:
In this comparative in vivo study of dendritic calcium accumulation, we describe the time course and spatial integration properties of two classes of visual interneurons in the lobula plate of the blowfly. Calcium accumulation was measured during visual motion stimulation, ensuring synaptic activation of the neurons within their natural spatial and temporal operating range. The compared cell classes, centrifugal horizontal (CH) and horizontal system (HS) cells, are known to receive retinotopic input of similar direction selectivity, but to differ in morphology, biophysics, presence of dendrodendritic synapses, and computational task. 1) The time course of motion-induced calcium accumulation was highly invariant with respect to stimulus parameters such as pattern contrast and size. In HS cells, the rise of [Ca2+]i can be described by a single exponential with a time constant of 5–6 s. The initial rise of [Ca2+]i in CH cells was much faster (τ ≈ 1 s). The decay time constant in both cell classes was estimated to be at least 3.5 times longer than the corresponding rise time constant. 2) The voltage-[Ca2+]i relationship was best described by an expansive nonlinearity in HS cells and an approximately linear relationship in CH cells. 3) Both cell classes displayed a size-dependent saturation nonlinearity of the calcium accumulation. Although in CH cells calcium saturation was indistinguishable from saturation of the membrane potential, saturation of the two response parameters differed in HS cells. 4) There was spatial overlap of the calcium signal in response to nonoverlapping visual stimuli. Both the area and the amplitude of the overlap profile was larger in CH cells than in HS cells. Thus calcium accumulation in CH cells is spatially blurred to a greater extent than in HS cells. 5) The described differences between the two cell classes may reflect the following computational tasks of these neurons: CH cells relay retinotopic information within the lobula plate via dendritic synapses with pronounced spatial low-pass filtering. HS cells are output neurons of the lobula plate, in which the slow, local calcium accumulation may be suitable for local modulatory functions.
29
Farshchian, Ali, Alessandra Sciutti, Assaf Pressman, Ilana Nisky, and Ferdinando A. Mussa-Ivaldi. "Energy exchanges at contact events guide sensorimotor integration." eLife 7 (May 29, 2018). http://dx.doi.org/10.7554/elife.32587.
Full textAbstract:
The brain must consider the arm’s inertia to predict the arm's movements elicited by commands impressed upon the muscles. Here, we present evidence suggesting that the integration of sensory information leading to the representation of the arm's inertia does not take place continuously in time but only at discrete transient events, in which kinetic energy is exchanged between the arm and the environment. We used a visuomotor delay to induce cross-modal variations in state feedback and uncovered that the difference between visual and proprioceptive velocity estimations at isolated collision events was compensated by a change in the representation of arm inertia. The compensation maintained an invariant estimate across modalities of the expected energy exchange with the environment. This invariance captures different types of dysmetria observed across individuals following prolonged exposure to a fixed intermodal temporal perturbation and provides a new interpretation for cerebellar ataxia.
30
Bae, Gi-Yeul. "The time course of face representations during perception and working memory maintenance." Cerebral Cortex Communications, December 15, 2020. http://dx.doi.org/10.1093/texcom/tgaa093.
Full textAbstract:
Abstract Successful social communication requires accurate perception and maintenance of invariant (face identity) and variant (facial expression) aspects of faces. While numerous studies investigated how face identity and expression information is extracted from faces during perception, less is known about the temporal aspects of the face information during perception and working memory (WM) maintenance. To investigate how face identity and expression information evolve over time, I recorded EEG while participants were performing a face WM task where they remembered a face image and reported either the identity or the expression of the face image after a short delay. Using multivariate ERP decoding analyses, I found that the two types of information exhibited dissociable temporal dynamics: Whereas face identity was decoded better than facial expression during perception, facial expression was decoded better than face identity during WM maintenance. Follow-up analyses suggested that this temporal dissociation was driven by differential maintenance mechanisms: Face identity information was maintained in a more ‘activity-silent’ manner compared to facial expression information, presumably because invariant face information does not need to be actively tracked in the task. Together, these results provide important insights into the temporal evolution of face information during perception and WM maintenance.
31
Rizzetta, Donald P., and Miguel R. Visbal. "Investigation of Transition Delay by Dynamic Surface Deformation." Journal of Fluids Engineering 141, no. 12 (June 17, 2019). http://dx.doi.org/10.1115/1.4043859.
Full textAbstract:
Numerical calculations were carried out to investigate control of transition on a flat plate by means of local dynamic surface deformation. The configuration and flow conditions are similar to a previous computation which simulated transition mitigation. Physically, the surface modification may be produced by piezoelectrically driven actuators located below a compliant aerodynamic surface, which have been employed experimentally. One actuator is located in the upstream plate region and oscillated at the most unstable frequency of 250 Hz to develop disturbances representing Tollmien–Schlichting instabilities. A controlling actuator is placed downstream and oscillated at the same frequency, but with an appropriate phase shift and modified amplitude to decrease disturbance growth and delay transition. While the downstream controlling actuator is two-dimensional (spanwise invariant), several forms of upstream disturbances were considered. These included disturbances which were strictly two-dimensional, those which were modulated in amplitude and those which had a spanwise variation of the temporal phase shift. Direct numerical simulations were obtained by solution of the three-dimensional compressible Navier–Stokes equations, utilizing a high-fidelity computational scheme and an implicit time-marching approach. A previously devised empirical process was applied for determining the optimal parameters of the controlling actuator. Results of the simulations are described, features of the flowfields elucidated, and comparisons made between solutions of the uncontrolled and controlled cases for the respective incoming disturbances. It is found that the disturbance growth is mitigated and the transition is delayed for all forms of the upstream perturbations, substantially reducing the skin friction.
32
Darabi, Nima, and U. Peter Svensson. "Dynamic Systems Approach in Sensorimotor Synchronization: Adaptation to Tempo Step-Change." Frontiers in Physiology 12 (June 21, 2021). http://dx.doi.org/10.3389/fphys.2021.667859.
Full textAbstract:
This paper presents a dynamic systems model of a sensorimotor synchronization (SMS) task. An SMS task typically gives temporally discrete human responses to some temporally discrete stimuli. Here, a dynamic systems modeling approach is applied after converting the discrete events to regularly sampled time signals. To collect data for model parameter fitting, a previously published pilot study was expanded. Three human participants took part in an experiment: to tap a finger on a keyboard, following a metronome which changed tempo in steps. System identification was used to estimate the transfer function that represented the relationship between the stimulus and the step response signals, assuming a separate linear, time-invariant system for each tempo step. Different versions of model complexity were investigated. As a minimum, a second-order linear system with delay, two poles, and one zero was needed to model the most important features of the tempo step response by humans, while an additional third pole could give a somewhat better fit to the response data. The modeling results revealed the behavior of the system in two distinct regimes: tempo steps below and above the conscious awareness of tempo change, i.e., around 12% of the base tempo. For the tempo steps above this value, model parameters were derived as linear functions of step size for the group of three participants. The results were interpreted in the light of known facts from other fields like SMS, psychoacoustics and behavioral neuroscience.
33
Vieweg, Paula, and Matthias M. Müller. "Shifting Attention in Feature Space: Fast Facilitation of the To-Be-Attended Feature Is Followed by Slow Inhibition of the To-Be-Ignored Feature." Journal of Cognitive Neuroscience, December 30, 2020, 1–10. http://dx.doi.org/10.1162/jocn_a_01669.
Full textAbstract:
In an explorative study, we investigated the time course of attentional selection shifts in feature-based attention in early visual cortex by means of steady-state visual evoked potentials (SSVEPs). To this end, we presented four flickering random dot kinematograms with red/blue, horizontal/vertical bars, respectively. Given the oscillatory nature of SSVEPs, we were able to investigate neural temporal dynamics of facilitation and inhibition/suppression when participants shifted attention either within (i.e., color to color) or between feature dimensions (i.e., color to orientation). Extending a previous study of our laboratory [Müller, M. M., Trautmann, M., & Keitel, C. Early visual cortex dynamics during top–down modulated shifts of feature-selective attention. Journal of Cognitive Neuroscience, 28, 643–655, 2016] to a full factorial design, we replicated a critical finding of our previous study: Facilitation of color was quickest, regardless of the origin of the shift (from color or orientation). Furthermore, facilitation of the newly to-be-attended and inhibition/suppression of the then to-be-ignored feature is not a time-invariant process that occurs instantaneously, but a biphasic one with longer time delays between the two processes. Interestingly, inhibition/suppression of the to-be-ignored feature after the shifting cue had a much longer latency with between- compared to within-dimensional shifts (by about 130–150 msec). The exploratory nature of our study is reasoned by two limiting factors: (a) Identical to our precursor study, we found no attentional SSVEP amplitude time course modulation for orientation, and (b) the signal-to-noise ratio for single trials was too poor to allow for reliable statistical testing of the latencies that were obtained with running t tests of averaged data.