Cortical transformation of spatial processing for solving the cocktail party problem: a computational model(1,2,3).

In multisource, "cocktail party" sound environments, human and animal auditory systems can use spatial cues to effectively separate and follow one source of sound over competing sources. While mechanisms to extract spatial cues such as interaural time differences (ITDs) are well understood in precortical areas, how such information is reused and transformed in higher cortical regions to represent segregated sound sources is not clear. We present a computational model describing a hypothesized neural network that spans spatial cue detection areas and the cortex. This network is based on recent physiological findings that cortical neurons selectively encode target stimuli in the presence of competing maskers based on source locations (Maddox et al., 2012). We demonstrate that key features of cortical responses can be generated by the model network, which exploits spatial interactions between inputs via lateral inhibition, enabling the spatial separation of target and interfering sources while allowing monitoring of a broader acoustic space when there is no competition. We present the model network along with testable experimental paradigms as a starting point for understanding the transformation and organization of spatial information from midbrain to cortex. This network is then extended to suggest engineering solutions that may be useful for hearing-assistive devices in solving the cocktail party problem.R01 DC000100 - NIDCD NIH HHSPublished versio

A physiologically inspired model for solving the cocktail party problem.

At a cocktail party, we can broadly monitor the entire acoustic scene to detect important cues (e.g., our names being called, or the fire alarm going off), or selectively listen to a target sound source (e.g., a conversation partner). It has recently been observed that individual neurons in the avian field L (analog to the mammalian auditory cortex) can display broad spatial tuning to single targets and selective tuning to a target embedded in spatially distributed sound mixtures. Here, we describe a model inspired by these experimental observations and apply it to process mixtures of human speech sentences. This processing is realized in the neural spiking domain. It converts binaural acoustic inputs into cortical spike trains using a multi-stage model composed of a cochlear filter-bank, a midbrain spatial-localization network, and a cortical network. The output spike trains of the cortical network are then converted back into an acoustic waveform, using a stimulus reconstruction technique. The intelligibility of the reconstructed output is quantified using an objective measure of speech intelligibility. We apply the algorithm to single and multi-talker speech to demonstrate that the physiologically inspired algorithm is able to achieve intelligible reconstruction of an "attended" target sentence embedded in two other non-attended masker sentences. The algorithm is also robust to masker level and displays performance trends comparable to humans. The ideas from this work may help improve the performance of hearing assistive devices (e.g., hearing aids and cochlear implants), speech-recognition technology, and computational algorithms for processing natural scenes cluttered with spatially distributed acoustic objects.R01 DC000100 - NIDCD NIH HHSPublished versio

D-Brane Dynamics in Dp-Brane Background

By using Dirac-Born-Infeld action we study the real time dynamics of D-branes in the vicinity of a stack of Dp-branes where the role of the tachyon of the open string models is played by the radial mode on the D-branes. We examine the behaviour of the tachyon potential and study the hamiltonian formulation and classical solutions of such systems. We also study the homogeneous solutions of the classical equations of motion in these cases.Comment: 14 pages, minor modifications, to appear in Phys. Lett.

D-brane Bound States from Charged Macroscopic Strings

We construct new D-brane bound states using charged macroscopic type IIB string solutions.A generic bound state solution, when dimensionally reduced, carries multiple gauge charges. Starting with D=9 charged macroscopic strings, we obtain solutions in D=10, which are interpreted as carrying (F, D0, D2) charges as well as nonzero momenta. The masses and charges are also explicitly shown to satisfy the non-threshold bound of 1/2 BPS objects. Our solutions reduce to the known D-brane bound state solutions with appropriate restrictions in the parameter space. We further generalize the results to (Dp- D(p+2)) bound state in IIA/B theories, giving an explicit example with p=1.Comment: 21 pages, latex, few references added: minor modification

A biologically orientated algorithm for spatial sound segregation

Listening in an acoustically cluttered scene remains a difficult task for both machines and hearing-impaired listeners. Normal-hearing listeners accomplish this task with relative ease by segregating the scene into its constituent sound sources, then selecting and attending to a target source. An assistive listening device that mimics the biological mechanisms underlying this behavior may provide an effective solution for those with difficulty listening in acoustically cluttered environments (e.g., a cocktail party). Here, we present a binaural sound segregation algorithm based on a hierarchical network model of the auditory system. In the algorithm, binaural sound inputs first drive populations of neurons tuned to specific spatial locations and frequencies. The spiking response of neurons in the output layer are then reconstructed into audible waveforms via a novel reconstruction method. We evaluate the performance of the algorithm with a speech-on-speech intelligibility task in normal-hearing listeners. This two-microphone-input algorithm is shown to provide listeners with perceptual benefit similar to that of a 16-microphone acoustic beamformer. These results demonstrate the promise of this biologically inspired algorithm for enhancing selective listening in challenging multi-talker scenes.NIHPublished versio

A PHM System Approach: Application to a Simplified Aircraft Bleed System

Regarding Prognostics and Health Management (PHM), the stakes lie in system-level prognostics or even the prognostics of systems of systems, as decisions are usually made at system or platform level. In this paper, a method, which takes into account both the system redundancy and the adaptation of operational modes in degraded functioning, is proposed and formalized. This method makes the system-level prognostics more relevant. The main feature of the method is to re-compute the components Remaining Useful Life (RUL) using the degradation rate associated to the future operating mode(s) due to system reconfiguration. This results in an improvement of both the System (SRUL) and the components . The proposed method is applied on a simplified aircraft bleed valve system to illustrate its effectiveness. This method is primarily destined to aeronautic systems, which are usually resilient. It has not been tested whether or not it could be useful in other fields

Magnetic Resonance Cholangiopancreatography in 3 Tesla: 2D MRCP versus 3D MRCP in Diagnostic Evaluation with Special Reference to Different Acquisition and Reconstruction Planes

Purpose: Magnetic resonance cholangiopancreatography (MRCP) is an established technique for the evaluation of intra- and extrahepatic bile ducts in patients with known or suspected hepatobiliary disease. However, the ideal acquisition and reconstruction plane for optimal bile duct evaluation with 3D technique has not been evaluated.The purpose of our study was to compare different acquisition and reconstruction planes of 3D MRCP for bile duct assessment. Methods: 51 consecutive adult patients suspected to have pancreatico-biliary disease were examined with 3 Tesla (Philips 3 T Ingenia) system both a multi thin slice (3D) and a breath-hold (Single Shot) MRCP technique were performed. In the multi thin slice technique both source images and maximum intensity projections were examined. Two radiologists blinded to clinical information viewed both MRCP techniques independantly. Measure of correlation between each of the techniques and the inter observer agreement were computed. Coronal and axial MIP were reconstructed based on each dataset (resulting in two coronal and two axial MIP, respectively) and assessed the MIP, regarding visualization of bile ducts and image quality.Results were compared (Wilcoxon test). Intra- and interobserver variability were calculated (kappa-statistic). Results: In case of coronal data acquisition, visualization of bile duct segments was significantly better on coronal reconstructed MIP images as compared to axial reconstructed MIP (p \u3c 0.05). Regarding visualization, coronal MIP of the coronal acquisition were equal to coronal MIP of the axial acquisition (p \u3e 0.05). Image quality of coronal and axial datasets did not differ significantly. Obstruction due to tumor was shown in 30% of patients, and calculi in the common bile duct were shown also in 30% of patients employing the 3D MRCP technique. Obstruction due to tumor and calculi were shown in 30% and 21% of patients, respectively, using the SS 2D MRCP technique. Sensitivity and specificity in distinguishing calculi in the common bile duct by 3D MRCP and SS MRCP were 100%, 100%, 70% and 100% respectively. Conclusions: Although the 3D MRCP multislice technique is more time consuming than the SS MRCP breath-hold technique at a 3 Tesla (Philips 3 T Ingenia) system it is advisable to use thin slice 3D MRCP in order not to misdiagnose calculi in the common bile duct.The results of our study suggest that for visualization and evaluation of intra- and extrahepatic bile duct segments reconstructed images in coronal orientation are preferable

Cyclic Correlation of Diffuse Reflected Signal with Glucose Concentration and scatterer size

The utility of optical coherence tomography signal intensity for measurement of glucose concentration has been analysed in tissue phantom and blood samples from human subjects. The diffusion equation based calculations as well as in-vivo OCT signal measurements confirms the cyclic correlation of signal intensity with glucose concentration and scatterer size.Comment: Four figures, Five page