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The underlying mechanism of how the human brain solves the cocktail party problem is largely unknown. Recent neuroimaging studies, however, suggest salient temporal correlations between the auditory neural response and the attended auditory object. Using magnetoencephalography (MEG) recordings of the neural responses of human subjects, we propose a decoding approach for tracking the attentional state while subjects are selectively listening to one of the two speech streams embedded in a competing-speaker environment. We develop a biophysically-inspired state-space model to account for the modulation of the neural response with respect to the attentional state of the listener. The constructed decoder is based on a maximum a posteriori (MAP) estimate of the state parameters via the Expectation Maximization (EM) algorithm. Using only the envelope of the two speech streams as covariates, the proposed decoder enables us to track the attentional state of the listener with a temporal resolution of the order of seconds, together with statistical confidence intervals. We evaluate the performance of the proposed model using numerical simulations and experimentally measured evoked MEG responses from the human brain. Our analysis reveals considerable performance gains provided by the state-space model in terms of temporal resolution, computational complexity and decoding accuracy.
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Atención/fisiología , Percepción Sonora/fisiología , Percepción del Habla/fisiología , Estimulación Acústica , Adulto , Algoritmos , Percepción Auditiva/fisiología , Ambiente , Femenino , Humanos , Magnetoencefalografía , Masculino , Modelos Neurológicos , Adulto JovenRESUMEN
Modification of terminal acceptors of non-fullerene organic solar cell molecule with different terminal acceptors can help in screening of molecules to develop organic photovoltaic cells with improved performance. Thus, in this work, seven new molecules with an unfused core have been designed and thoroughly investigated. DFT/TD-DFT simulations were performed on studied molecules to explore the ground and excited state characteristics. UV-Visible analysis revealed the red shift in the absorption spectrum (reaching 781 nm) owing to their smaller energy gap up to 1.94 eV. Furthermore, transition density matrix analysis demonstrated that peripheral acceptors extract the electron density from the core effectively. The effectiveness of our investigated molecules as materials for high-performing organic photovoltaic cells has been shown by an examination of their electron and hole mobilities for fast charge transfer. When combined with PTB7-Th, all molecules displayed high open circuit voltage. XP5 molecule exhibited highest open circuit voltage (1.70 eV) and lowest energy loss of 0.30 eV. All designed molecules exhibit the improved aforementioned parameters, which shows that these molecules can be used to develop competent solar devices in future.
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ElectronesRESUMEN
This study focused on modeling and density functional theory (DFT) analysis of reference (AI1) and designed structures (AI11-AI15), based on the thieno-imidazole core, in order to create profitable candidates for solar cells. All the optoelectronic properties of the molecular geometries were computed using DFT and time dependent-DFT approaches. The influence of terminal acceptors on the bandgaps, absorption, hole and electron mobilities, charge transfer capabilities, fill factor, dipole moment, etc. Of the recently designed structures (AI11-AI15), as well as reference (AI1), were evaluated. Optoelectronics and chemical parameters of newly architecture geometries were shown to be superior to the cited molecule. The FMOs and DOS graphs also demonstrated that the linked acceptors remarkably improved the dispersion of charge density in the geometries under study, particularly in AI11 and AI14. Calculated values of binding energy and chemical potential confirmed the thermal stability of the molecules. All the derived geometries surpassed the AI1 (Reference) molecule in terms of maximum absorbance ranging from 492 to 532 nm (in chlorobenzene solvent) and a narrower bandgap ranging from 1.76 to 1.99eV. AI15 had the lowest exciton dissociation energy of 0.22eV as well as lowest electrons and hole dissociation energies, while AI11 and AI14 showed highest VOC, fill factor, power conversion efficiency (PCE), IP and EA (owing to presence of strong electron pulling cyano (CN) moieties at their acceptor portions and extended conjugation) than all the examined molecules, implying that they could be used to build elite solar cells with enhanced photovoltaic attributes.
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Electrones , Cloruro de Sodio , Teoría Funcional de la Densidad , SolventesRESUMEN
The competence of organic solar cells (OSCs) could be enhanced by improving the light absorption capabilities as well as the open-circuit voltage (Voc) of utilized molecules. To upgrade overall functionality of OSCs, seven new molecules were designed in this work using an end-cap alteration technique on Quinoxaline fused core-based non-fullerene acceptor (Qx-2) molecule. This technique is known to be quite advantageous in terms of improvement of the effectiveness and optoelectrical behavior of various OSCs. Critical parameters like the absorption maximum, frontier molecular orbitals, excitation energy, exciton binding energy, Voc, and fill factor of molecules were considered for the molecules thus designed. All newly designed molecules showed outstanding improvement in optoelectronic as well as performance-related properties. Out of all scrutinized molecules, Q1 exhibited highest wavelength of absorption peak (λmax = 779 nm) with the reduced band gap (1.90 eV), least excitation energy (Ex = 1.59 eV), along with the highest dipole moment (17.982950 D). Additionally, the newly designed compounds Q4, Q5, and Q6 exhibited significantly improved Vocs that were 1.55, 1.47, and 1.50 eV accordingly, as compared to the 1.37 eV of Qx-2 molecule. These molecules also showed remarkable improvement in fill factor attributed to direct correspondence of Voc with it. Inclusively, these results support the superiority of these newly developed molecules as prospective constituents of upgraded OSCs.
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Quinoxalinas , Estudios ProspectivosRESUMEN
Despite the substantial advancements in organic solar cells (OSCs), the best devices still have quite low efficiencies due to less focus on donor molecules. With the intention to present efficient donor materials, seven small donor molecules (T1-T7) were devised from DRTB-T molecule by using end-capped modeling. Newly designed molecules exhibited remarkable improved optoelectronic properties such as less band gap (from 2.00 to 2.23 eV) than DRTB-T having band gap of 2.57 eV. Similarly, a significant improvement in λmax values was noticed in designed molecules in gaseous medium (666 nm-738 nm) and solvent medium (691 nm-776 nm) than DRTB-T having λmax values at 568 nm and 588 nm in gas and solvent phase respectively. Among all molecules, T1 and T3 exhibited significant improvement in optoelectronic properties such as narrow band gap, lower excitation energy, higher λmax values and lower electron reorganization energy as compared to pre-existed DRTB-T molecule. The better functional ability of T1-T7 is also suggested by an improvement in open circuit voltage (Voc) of designed structures (1.62 eV-1.77 eV) as compared to R (1.49 eV) when PC61BM is used as an acceptor. So, all our newly derived donors can be employed in the active layer of organic solar cells to manufacture efficient OSCs.
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Electrones , Gases , SolventesRESUMEN
To intensify the photovoltaic properties of organic solar cells, density functional theory (DFT) based computational techniques were implemented on six non-fullerene A-D-A type small molecules (N1-N6) modified from reference molecule (R) which consists of phenazine fused with 1,4- Dimethyl-4H-3,7-dithia-4-aza- cyclopenta [α] pentalene on both sides with one of its phenyl rings acting as the central donor unit, further attached with 2-(5,6-Difluoro-2-methylene-3-oxo-indan-1-ylidene)-malononitrile acceptor groups at terminal sites. All proposed compounds have a phenazine base modified with a variety of substituents at the terminals. Transition density matrix, density of states, frontier molecular orbitals, intramolecular charge transfer abilities and optoelectronic properties of these compounds were investigated using B3LYP/6-31G (d, p) and B3LYP/6-31G++ (d,p) level of theory. All six designed compounds exhibited a bathochromic sift in their λmax as compared to the R molecule. All designed molecules also have reduced band gap and smaller excitation energy than R. Among all, N6 exhibited highest λmax and lowest bandgap as compared to reference molecule indicating its promising photovoltaic properties. Decreased hole and electron reorganization energy in several of the suggested compounds is indicative of greater charge mobility in them. PTB7-Th donor was employed to calculate open circuit voltage of all investigated molecules. N1-N5 molecules had improved optoelectronic properties, significant probable power conversion efficiency as evident from their absorption aspects, high values of Voc, and fill factor, compared to R molecule. Designed A-D-A type NF based molecules make OSCs ideal for use in wearable devices, building-integrated photovoltaics and smart fabrics.
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Osteosclerosis , Fenazinas , Humanos , ElectronesRESUMEN
Modifying the central core is a very efficient strategy to boost the performance of non-fullerene acceptors. Herein five non-fullerene acceptors (M1-M5) of A-D-D'-D-A type were designed by substituting the central acceptor core of the reference (A-D-A'-D-A type) with different strongly conjugated and electron donating cores (D') to enhance the photovoltaic attributes of OSCs. All the newly designed molecules were analyzed through quantum mechanical simulations to compute their optoelectronic, geometrical, and photovoltaic parameters and compare them to the reference. Theoretical simulations of all the structures were carried out through different functionals with a carefully selected 6-31G(d,p) basis set. Absorption spectra, charge mobility, dynamics of excitons, distribution pattern of electron density, reorganization energies, transition density matrices, natural transition orbitals and frontier molecular orbitals, respectively of the studied molecules were evaluated at this functional. Among the designed structures in various functionals, M5 showed the most improved optoelectronic properties, such as the lowest band gap (2.18 e V), highest maximum absorption (720 nm), and lowest binding energy (0.46 eV) in chloroform solvent. Although the highest photovoltaic aptitude as acceptors at the interface was perceived to be of M1, its highest band gap and lowest absorption maxima lowered its candidature as the best molecule. Thus, M5 with its lowest electron reorganization energy, highest light harvesting efficiency, and promising open-circuit voltage (better than the reference), amongst other favorable features, outperformed the others. Conclusively, each evaluated property commends the aptness of designed structures to augment the power conversion efficiency (PCE) in the field of optoelectronics in one way or another, which reveals that a central un-fused core having an electron-donating capability with terminal groups being significantly electron withdrawing, is an effective configuration for the attainment of promising optoelectronic parameters, and thus the proposed molecules could be utilized in future NFAs.
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Among the blended components of a photoactive layer in organic photovoltaic (OPV) cells, the acceptor is of high importance. This importance is attributed to its increased ability to withdraw electrons toward itself for their effective transport toward the respective electrode. In this research work, seven new non-fullerene acceptors were designed for their possible utilization in the OPVs. These molecules were designed through side-chain engineering of the PTBTP-4F molecule, with its fused pyrrole ring-based donor core and different strongly electron-withdrawing acceptors. To elucidate their effectiveness, the band gaps, absorption characteristics, chemical reactivity indices, and photovoltaic parameters of all of the architecture molecules were compared with the reference. Through various computational software, transition density matrices, graphs of absorption, and density of states were also plotted for these molecules. From some chemical reactivity indices and electron mobility values, it was proposed that our newly designed molecules could be better electron-transporting materials than the reference. Among all, TP1, due to its most stabilized frontier molecular orbitals, lowest band gap and excitation energies, highest absorption maxima in both the solvent and gas medium, least hardness, highest ionization potential, superior electron affinity, lowest electron reorganization energy, as well as highest rate constant of charge hopping, seemed to be the best molecule in terms of its electron-withdrawing abilities in the photoactive layer blend. In addition, in terms of all of the photovoltaic parameters, TP4-TP7 was perceived to be better suited in comparison to TPR. Thus, all our suggested molecules could act as superior acceptors to TPR.
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In the present research work, four novel triphenylamine (TPA)-based acceptor molecules have been architectured to step up the solar efficiency of organic solar cells. The four designed molecules abbreviated as T1-T4 have a common TPA donor core and different strong electron pulling peripheral acceptor groups connected through thiophene spacers. Computational simulations of T1-T4 were performed to compute and compare their optoelectronic properties with well-known reference molecule S(TPA-DPP) designated as R in the current project. For geometric optimizations of designed molecules, MPW1PW91 functional along with a basis set of 6-31G (d, p) was enforced. Assessment of the optoelectronic features of newly reported 3-D molecules (T1-T4) has been executed through density functional theory (DFT) and time-dependent density functional theory (TD-DFT) computations. Transition density matrix (TDM) and density of state (DOS) evaluations were performed for the investigation of exciton dynamics and electronic contribution between two states. All the derived molecules exhibited admirable photovoltaic features when compared to that of the reference molecule. Amidst all these newly modified molecules, T3 manifested itself as the finest candidate having the least energy band gap (1.84 eV) and the highest λmax (865 nm) in dichloromethane solvent. Also, T1 molecule has the lowest hole reorganization energy (0.0036 eV) value. These designed candidates (T1-T4) confirm that peripheral acceptor tempering is an effectual approach for the attainment of the desirable optoelectronic properties.
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Electrónica , Tiofenos , Teoría Funcional de la DensidadRESUMEN
With the aim of utilizing structural modeling techniques to design efficient organic solar cells, a quantum chemical density functional theory (DFT) and its time-dependent DFT (TD-DFT) study have been carried out for the examination of the photovoltaic properties of four BT-ClC-based novel non-fullerene acceptor (NFA) molecules. The designed entities (BT1-BT4) have an A-π-D-π-A configuration with seven fused ring-based BDT central core and newly substituted peripheral acceptor moieties. The optical parameters (absorption maxima, light-harvesting efficiency, first excitation energies, and dipole moments), electronic properties (frontier molecular orbitals, density of states, and molecular electrostatic potential), and charge transfer characteristics (open-circuit voltage, transition density matrix, and fill factor) of the investigated molecules were evaluated using the selected B3LYP/6-31G (d,p) level of theory. The systematic computational analysis reveals that under the influence of terminal acceptor groups, there is an augmentation in the absorption range, and reduction in the band gap values. The electron withdrawing effect of acceptor moieties is evident from the electronic density distribution on the HOMO-LUMO orbitals, along with the density of state (DOS) graphs. Transition density matrix (TDM) analyses reveal consistent charge transfer in the newly devised entities. Reorganization energies computed for electron and hole are significantly lower than the reference, making the transfer of charge carriers efficient. Open-circuit voltage (Voc) of reported acceptor entities, theoretically computed with PTB7-Th donor, revealed maximum output. Furthermore, the estimated fill factor (FF) of the investigated molecules predicted an increase in power conversion efficiencies. Consequently, all the computed parameters favor the applicability of our designed molecules in the field of organic photovoltaics by virtue of their excellent charge mobilities, increased absorption maximum values, and reduced band gaps.
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Electrones , Teoría Funcional de la Densidad , Electricidad EstáticaRESUMEN
Density functional theory, along with its time dependent computational approach were employed in order to fine tune the photovoltaic attributes along with the efficiency of the MO-IDIC-2F molecule. Thus, five new molecules were designed by substitution of the different notable acceptor fragments in the MO-IDIC-2F molecule, along with the addition of the "[1, 2, 5] thiadiazolo[3,4-d] pyridazine" spacer moieties between donor core and newly substituted acceptor groups. In this research work, various photovoltaic properties, which could affect the efficiency of an organic chromophores, such as bandgap, oscillator strength, dipole moment, binding energy, light-harvesting efficiency, etc. were studied. All the newly proposed molecules demonstrated significantly improved outcomes in comparison to that of the reference molecule, in their absorption spectrum, excitation, as well as binding energy values, etc. In order to confirm the results of optoelectronic properties, density of states, transition density matrix, and electrostatic potential analyses of molecules were also performed, which supported our computational findings. All of the results confirmed the high potential of all the newly proposed molecules for the development of improved OSCs.
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Suministros de Energía EléctricaRESUMEN
Four acceptor-donor-acceptor (A-D-A) type cyclopentadithiophene core-based non-fullerene small acceptor molecules were designed with the objective to improve the proficiency of photovoltaic cells. A comprehensive density functional theory (DFT) analysis was done by employing B3LYP functional with 6-31G(d,p) basis set to study optoelectronic properties of R as well as M1-M4 molecules, while the time-dependent self-consistent field (TDSCF) was utilized to analyze their excited state calculations. Several essential characteristics must be refined in order to enhance the efficiency of small molecular acceptors, i.e., the density of states (DOS), HOMO-LUMO band gap, transition density matrix (TDM), dipole moment, reorganization energy, light-harvesting efficiency, and open-circuit voltage, etc. In comparison to the R molecule, all the derived molecules show better maximum absorption (in chloroform solvent) with a range of 886-951 nm and a smaller band gap with a range of 1.65-1.55 eV M2 retains the least exciton binding energy of 0.24 eV, and amongst all the investigated molecules M3 molecule has the least interaction coefficient values so, it possesses better charge transport probability. The reorganization energy values in eV for both electron (0.00579) and hole (0.00737) are the least for M3 molecule, so this molecule exhibits better charge mobility for electron and hole. VOC of R and M1-M4 molecule was calculated by theoretically computing the values of their complexes with PTB7-Th donor molecule.
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To investigate the consequence of different substitution positions of various π-linkers on the photovoltaic properties of an organic solar cell molecule, we have introduced two series of six three-donor molecules, by the substitution of some effective π-linkers on the A-π-D-π-A type reference molecule IECIO-4F (taken as IOR). In series "a" the thienyl or furyl bridge is directly linked between the donor and acceptor moieties, while in series "b" the phenyl ring of the same bridge is working as the direct point of attachment. The frontier molecular orbitals, density of states, transition density matrix, molecular electrostatic potential surfaces, exciton binding energy, excitation energy, wavelength of maximum absorption, open-circuit voltage, fill factor, and some other photovoltaic attributes of the proposed molecules were analyzed through density functional theory (DFT) and its time-dependent (TD) approach; the TD-DFT method. Though both series of newly derived molecules were a step up from the reference molecule in almost all of the studied characteristics, the "a" series (IO1a to IO3a) seemed to be better due to their desirable properties such as the highest maximum absorption wavelength (λ max), open-circuit voltage, and fill factor, along with the lowest excitation and exciton dissociation energy, etc. of its molecules. Also, the studied morphology, optical characteristics, and electronic attributes of this series of proposed molecules signified the fact that the molecules with thienyl or furyl ring working as the direct link between the acceptor and donor molecules showed enhanced charge transfer abilities, and could provide a maximum quantum yield of the solar energy supplied.
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In this research work, four new molecules from the π-A-π-D-π-A-π type reference molecule "DBS-2PP", were designed for their potential application in organic solar cells by adding peripheral A2 acceptors to the reference. Under density functional theory, a comprehensive theoretical investigation was conducted to examine the structural geometries, along with the optical and photovoltaic parameters; comprising frontier molecular orbitals, density of states, light-harvesting effectiveness, excitation, binding, and reorganizational energies, molar absorption coefficient, dipole moment, as well as transition density matrix of all the molecules under study. In addition, some photo-voltaic characteristics (open circuit photo-voltage and fill factor) were also studied for these molecules. Although all the developed compounds (D1-D4) surpassed the reference molecule in the attributes mentioned above, D4 proved to be the best. D4 possessed the narrowest band-gap, as well as the highest absorption maxima and dipole moment of all the molecules in both the evaluated phases. Moreover, with PC61BM as the acceptor, D4 showed the maximum V OC and FF values. Furthermore, while D3 had the greatest hole mobility owing to its lowest value of hole reorganization energy, D4 exhibited the maximum electron mobility due to its lowermost value of electron reorganization energy. Overall, all the chromophores proposed in this study showed outstanding structural, optical, and photovoltaic features. Considering this, organic solar cell fabrication can be improved by using these newly derived donors at the donor-acceptor interfaces.
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In the current study, with the objective to improve the overall performance of organic solar cells, seven new W-shaped small molecular acceptors - were developed theoretically by the end-group alteration of the reference (WR) molecule. The MPW1PW91 functional with the basis set 6-31G(d,p) was used to explore the optoelectronic properties of the WR and W1-W7 molecules and the time-dependent self-consistent filed (TD-SCF) simulation was used to investigate the solvent-state calculations. The several explored photovoltaic attributes were the absorption spectra, excitation energies, bandgap between the FMOs, oscillator strength, full width at half maximum, light-harvesting efficiency, transition density matrices, open-circuit voltage, fill factor, density of states, binding energy, interaction coefficient, etc. Overall, the results revealed a bathochromic shift in the absorption maxima (λ max), a reduced HOMO-LUMO gap (E gap), and smaller excitation energy (E x) of the altered molecules as compared to the WR molecule. Some of the optoelectronic aspects of a well-known fused ring based acceptor named Y6 are also compared with the studied W-shaped molecules. Additionally, the W1 molecule presented the smallest E gap, along with highest λ max and the lowest E x, amongst all, in both the evaluated media (gas and solvent). The open circuit voltage (V OC) of all the considered small molecular acceptors was calculated by pairing them with the PTB7-Th donor. Here, W6 and W7 displayed the best results for the V OC (1.48 eV and 1.51 eV), normalized V OC (57.25 and 58.41) and FF (0.9131 and 0.9144). Consequently, in light of the results of this research, the altered molecules could be considered for practical implementation in the manufacturing of OSCs with improved photovoltaic capabilities.
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Humans are able to identify and track a target speaker amid a cacophony of acoustic interference, an ability which is often referred to as the cocktail party phenomenon. Results from several decades of studying this phenomenon have culminated in recent years in various promising attempts to decode the attentional state of a listener in a competing-speaker environment from non-invasive neuroimaging recordings such as magnetoencephalography (MEG) and electroencephalography (EEG). To this end, most existing approaches compute correlation-based measures by either regressing the features of each speech stream to the M/EEG channels (the decoding approach) or vice versa (the encoding approach). To produce robust results, these procedures require multiple trials for training purposes. Also, their decoding accuracy drops significantly when operating at high temporal resolutions. Thus, they are not well-suited for emerging real-time applications such as smart hearing aid devices or brain-computer interface systems, where training data might be limited and high temporal resolutions are desired. In this paper, we close this gap by developing an algorithmic pipeline for real-time decoding of the attentional state. Our proposed framework consists of three main modules: (1) Real-time and robust estimation of encoding or decoding coefficients, achieved by sparse adaptive filtering, (2) Extracting reliable markers of the attentional state, and thereby generalizing the widely-used correlation-based measures thereof, and (3) Devising a near real-time state-space estimator that translates the noisy and variable attention markers to robust and statistically interpretable estimates of the attentional state with minimal delay. Our proposed algorithms integrate various techniques including forgetting factor-based adaptive filtering, â1-regularization, forward-backward splitting algorithms, fixed-lag smoothing, and Expectation Maximization. We validate the performance of our proposed framework using comprehensive simulations as well as application to experimentally acquired M/EEG data. Our results reveal that the proposed real-time algorithms perform nearly as accurately as the existing state-of-the-art offline techniques, while providing a significant degree of adaptivity, statistical robustness, and computational savings.
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In a complex auditory scene comprising multiple sound sources, humans are able to target and track a single speaker. Recent studies have provided promising algorithms to decode the attentional state of a listener in a competing-speaker environment from non-invasive brain recordings sun exhibit poor performance at temporal resolutions suitable for real-time implementation, which hinders their utilization in emerging applications such as smart hearich as electroencephalography (EEG). These algorithms require substantial training datasets and ofteng aids. In this work, we propose a real-time attention decoding framework by integrating techniques from Bayesian filtering, $\ell_{1}$-regularization, state-space modeling, and Expectation Maximization, which is capable of producing robust and statistically interpretable measures of auditory attention at high temporal resolution. Application of our proposed algorithm to synthetic and real EEG data yields a performance close to the state-of-the-art offline methods, while operating in near real-time with a minimal amount of training data.
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Atención , Teorema de Bayes , Electroencefalografía , Algoritmos , Percepción Auditiva , Encéfalo , Electroencefalografía/métodos , HumanosRESUMEN
OBJECTIVE: A central problem in computational neuroscience is to characterize brain function using neural activity recorded from the brain in response to sensory inputs with statistical confidence. Most of existing estimation techniques, such as those based on reverse correlation, exhibit two main limitations: first, they are unable to produce dynamic estimates of the neural activity at a resolution comparable with that of the recorded data, and second, they often require heavy averaging across time as well as multiple trials in order to construct statistical confidence intervals for a precise interpretation of data. In this paper, we address the above-mentioned issues for estimating auditory temporal response function (TRF) as a parametric computational model for selective auditory attention in competing-speaker environments. METHODS: The TRF is a sparse kernel which regresses auditory MEG data with respect to the envelopes of the speech streams. We develop an efficient estimation technique by exploiting the sparsity of the TRF and adopting an â1-regularized least squares estimator which is capable of producing dynamic TRF estimates as well as confidence intervals at sampling resolution from single-trial MEG data. RESULTS: We evaluate the performance of our proposed estimator using evoked MEG responses from the human brain in an auditory attention experiment with two competing speakers. The TRFs are estimated dynamically over time using the proposed technique with multisecond resolution, which is a significant improvement over previous results with a temporal resolution of the order of a minute. CONCLUSION: Application of our method to MEG data reveals a precise characterization of the modulation of M50 and M100 evoked responses with respect to the attentional state of the subject at multisecond resolution. SIGNIFICANCE: Our proposed estimation technique provides a high resolution real-time attention decoding framework in multispeaker environments with potential application in smart hearing aid technology.
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Atención/fisiología , Corteza Auditiva/fisiología , Mapeo Encefálico/métodos , Potenciales Evocados Auditivos/fisiología , Magnetoencefalografía/métodos , Percepción del Habla/fisiología , Adulto , Identificación Biométrica/métodos , Femenino , Humanos , Masculino , Reconocimiento de Normas Patrones Automatizadas/métodos , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Adulto JovenRESUMEN
A perceptual phenomenon is reported, whereby prior acoustic context has a large, rapid and long-lasting effect on a basic auditory judgement. Pairs of tones were devised to include ambiguous transitions between frequency components, such that listeners were equally likely to report an upward or downward 'pitch' shift between tones. We show that presenting context tones before the ambiguous pair almost fully determines the perceived direction of shift. The context effect generalizes to a wide range of temporal and spectral scales, encompassing the characteristics of most realistic auditory scenes. Magnetoencephalographic recordings show that a relative reduction in neural responsivity is correlated to the behavioural effect. Finally, a computational model reproduces behavioural results, by implementing a simple constraint of continuity for binding successive sounds in a probabilistic manner. Contextual processing, mediated by ubiquitous neural mechanisms such as adaptation, may be crucial to track complex sound sources over time.
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Corteza Auditiva/fisiología , Percepción Auditiva/fisiología , Audición/fisiología , Sonido , Estimulación Acústica , Algoritmos , Humanos , Juicio , Magnetoencefalografía , Modelos Teóricos , Percepción de la Altura Tonal/fisiología , Adulto JovenRESUMEN
Humans routinely segregate a complex acoustic scene into different auditory streams, through the extraction of bottom-up perceptual cues and the use of top-down selective attention. To determine the neural mechanisms underlying this process, neural responses obtained through magnetoencephalography (MEG) were correlated with behavioral performance in the context of an informational masking paradigm. In half the trials, subjects were asked to detect frequency deviants in a target stream, consisting of a rhythmic tone sequence, embedded in a separate masker stream composed of a random cloud of tones. In the other half of the trials, subjects were exposed to identical stimuli but asked to perform a different taskto detect tone-length changes in the random cloud of tones. In order to verify that the normalized neural response to the target sequence served as an indicator of streaming, we correlated neural responses with behavioral performance under a variety of stimulus parameters (target tone rate, target tone frequency, and the "protection zone", that is, the spectral area with no tones around the target frequency) and attentional states (changing task objective while maintaining the same stimuli). In all conditions that facilitated target/masker streaming behaviorally, MEG normalized neural responses also changed in a manner consistent with the behavior. Thus, attending to the target stream caused a significant increase in power and phase coherence of the responses in recording channels correlated with an increase in the behavioral performance of the listeners. Normalized neural target responses also increased as the protection zone widened and as the frequency of the target tones increased. Finally, when the target sequence rate increased, the buildup of the normalized neural responses was significantly faster, mirroring the accelerated buildup of the streaming percepts. Our data thus support close links between the perceptual and neural consequences of the auditory stream segregation.