Craig Jin

A new EEG recording system for passive dry electrodes

OBJECTIVE We present a new, low power EEG recording system with an ultra-high input impedance that enables the use of long-lasting, passive dry electrodes. It incorporates Bluetooth wireless connectivity and is designed to be suitable for long-term monitoring during daily activities. METHODS The new EEG system is compared to a standard and clinically available reference EEG system using wet electrodes in three separate sets of experiments. In the first two experiments, each dry electrode was surrounded by four standard wet electrodes and the alpha and mu-rhythms were recorded. In the third experiment, serial monopolar (referred to the left ear) recordings of flash visual evoked potential were performed using the new EEG system and a reference system. RESULTS These experiments showed that the signal recorded using the new EEG system is almost identical to that recorded with standard clinical EEG equipment; our measurements showed that the correlation coefficient between the dry electrode recordings and the average of the four standard electrodes surrounding each dry electrode is greater than 0.85. CONCLUSION We conclude that the new EEG system performs similarly to reference EEG systems, while providing the advantages of portability, ease of application and minimal scalp preparation. SIGNIFICANCE The proposed system using passive dry electrodes suitable for single use while performing as good as standard EEG equipment provides ease of application and minimal scalp preparation.

A mobile EEG system with dry electrodes

A new EEG recording device demonstrating an ultra-high input impedance is presented. Dry electrodes made of conductive rubber were employed for this study with careful shielding of the electrodes and cables. The device has a small form factor, so it is wearable, and has continuous Bluetooth connectivity. Tests were performed to assess features of the proposed device and to compare it with standard clinical devices. Simultaneous EEG recordings were measured from adjacent sites on the scalp using the new EEG device with dry electrodes and a reference EEG device with standard electrodes. The gain and bandwidth settings for the two devices were set similarly. Traditional closing eyes alpha-wave replacement and mu-rhythm were compared in both the time and frequency domains. Results from eight subjects show a high correlation coefficient (0.83 on average) between recordings of contiguous dry and standard electrodes. We conclude that the performance of the new device is comparable with standard EEG recording equipment, but offers a shorter set-up time, the possibility of long-term recording, and a wireless connection - all of which are advantages valuable in the field of brain computer interfaces and neurofeedback.

The role of high frequencies in speech localization

This study measured the accuracy with which human listeners can localize spoken words. A broadband (300 Hz-16 kHz) corpus of monosyllabic words was created and presented tolisteners using a virtual auditory environment. Localization was examined for 76 locations ona sphere surrounding the listener. Experiment 1 showed that low-pass filtering the speech sounds at 8 kHz degraded performance, causing an increase in polar angle errors associated with the cone of confusion. In experiment 2 it was found that performance in fact varied systematically with the level of the signal above 8 kHz. Although the lower frequencies (below 8 kHz) are known to be sufficient for accurate speech recognition in most situations, these results demonstrate that natural speech contains information between 8 and 16 kHz that is essential for accurate localization.

An Active 2-D Silicon Cochlea

In this paper, we present an analog integrated circuit design for an active 2-D cochlea and measurement results from a fabricated chip. The design includes a quality factor control loop that incorporates some of the nonlinear behavior exhibited in the real cochlea. This control loop varies the gain and the frequency selectivity of each cochlear resonator based on the amplitude of the input signal.

Benefit from spatial separation of multiple talkers in bilateral hearing-aid users: Effects of hearing loss, age, and cognition

Abstract To study the spatial hearing abilities of bilateral hearing-aid users in multi-talker situations, 20 subjects received fittings configured to preserve acoustic cues salient for spatial hearing. Following acclimatization, speech reception thresholds (SRTs) were measured for three competing talkers that were either co-located or spatially separated along the front-back or left-right dimension. In addition, the subjects’ working memory and attentional abilities were measured. Left-right SRTs varied over more than 14 dB, while front-back SRTs varied over more than 8 dB. Furthermore, significant correlations were observed between left-right SRTs, age, and low-frequency hearing loss, and also between front-back SRTs, age, and high-frequency aided thresholds. Concerning cognitive effects, left-right performance was most strongly related to attentional abilities, while front-back performance showed a relation to working memory abilities. Altogether, these results suggest that, due to raised hearing thresholds and aging, hearing-aid users have reduced access to interaural and monaural spatial cues as well as a diminished ability to ‘enhance’ a target signal by means of top-down processing. These deficits, in turn, lead to impaired functioning in complex listening environments. Sumario Para estudiar las habilidades auditivas espaciales de usuarios de audífonos bilaterales en situaciones de hablantes múltiples, 20 sujetos recibieron auxiliares configurados para preservar las más destacadas claves acústicas de la audición espacial. Después de un período de adaptación, se midieron los umbrales de recepción del habla (SRTs) con tres hablantes en competencia que fueron colocados cerca o espacialmente separados en las dimensiones frente-atrás o izquierda-derecha. Además, se midieron las habilidades de memoria activa y atención. Los SRTs izquierda-derecha variaron más de 14 dB mientras que los SRTs frente-atrás, variaron más de 8 dB. Más aún, se observaron correlaciones significativas entre SRTs frente-atrás, edad y pérdida auditiva en las frecuencias graves y también entre SRTs frente-atrás, edad y umbrales con auxiliares auditivos en las frecuencias agudas. En relación con los efectos cognitivos, el rendimiento izquierda-derecha se relacionó más firmemente con habilidades de atención, mientras que el rendimiento frente-atrás, mostró relación con habilidades de memoria activa. En general, estos resultados sugieren que, debido a la elevación de los umbrales auditivos y el envejecimiento, los usuarios de auxiliares auditivos tienen un acceso reducido a las claves espaciales interaurales y monoaurales así como una habilidad disminuida para “mejorar” una señal blanco por medio del procesamiento arriba-abajo. Estos déficits, a su vez, conducen a un funcionamiento disminuido en ambientes de escucha complejos.

A review on electrical impedance tomography for pulmonary perfusion imaging

Although electrical impedance tomography (EIT) for ventilation monitoring is on the verge of clinical trials, pulmonary perfusion imaging with EIT remains a challenge, especially in spontaneously breathing subjects. In anticipation of more research on this subject, we believe a thorough review is called for. In this paper, findings related to the physiological origins and electrical characteristics of this signal are summarized, highlighting properties that are particularly relevant to EIT. The perfusion impedance change signal is significantly smaller in amplitude compared with the changes due to ventilation. Therefore, the hardware used for this purpose must be more sensitive and more resilient to noise. In previous works, some signal- or image-processing methods have been required to separate these two signals. Three different techniques are reviewed in this paper, including the ECG-gating method, frequency-domain-filtering-based methods and a principal-component-analysis-based method. In addition, we review a number of experimental studies on both human and animal subjects that employed EIT for perfusion imaging, with promising results in the diagnosis of pulmonary embolism (PE) and pulmonary arterial hypertension as well as other potential applications. In our opinion, PE is most likely to become the main focus for perfusion EIT in the future, especially for heavily instrumented patients in the intensive care unit (ICU).

A log-domain implementation of the Izhikevich neuron model

We present an implementation of the Izhikevich neuron model which uses two first-order log-domain low-pass filters and two translinear multipliers. The neuron consists of a leaky-integrate-and-fire core, a slow adaptive state variable and quadratic positive feedback. Simulation results show that this neuron can emulate different spiking behaviours observed in biological neurons.

Upscaling Ambisonic sound scenes using compressed sensing techniques

This paper considers the application of compressed sensing to spherical acoustics in order to improve spatial sound field reconstruction. More specifically, we apply compressed sensing techniques to a set of Ambisonic sound signals to obtain a super-resolution plane-wave decomposition of the original sound field. That is to say, we investigate using the plane-wave decomposition to increase the spherical harmonic order of the Ambisonic sound scene. We refer to this as upscaling the Ambisonic sound scene. A focus of the paper is using sub-band analysis to make the plane-wave decomposition more robust. Results show that the sub-band analysis does indeed improve the robustness of the plane-wave decomposition when dominant overlapping sources are present or in noisy or diffuse sound conditions. Upscaling Ambisonic sound scenes allows more loudspeakers to be used for spatial sound field reconstruction, resulting in a larger sweet spot and improved sound quality.

An ultra-high input impedance ECG amplifier for long-term monitoring of athletes.

We present a new, low-power electrocardiogram (ECG) recording system with an ultra-high input impedance that enables the use of long-lasting, dry electrodes. The system incorporates a low-power Bluetooth module for wireless connectivity and is designed to be suitable for long-term monitoring during daily activities. The new system using dry electrodes was compared with a clinically approved ECG reference system using gelled Ag/AgCl electrodes and performance was found to be equivalent. In addition, the system was used to monitor an athlete during several physical tasks, and a good quality ECG was obtained in all cases, including when the athlete was totally submerged in fresh water.

Blind Image Watermarking Using a Sample Projection Approach

This paper presents a robust image watermarking scheme based on a sample projection approach. While we consider the human visual system in our watermarking algorithm, we use the low-frequency components of image blocks for data hiding to obtain high robustness against attacks. We use four samples of the approximation coefficients of the image blocks to construct a line segment in the 2-D space. The slope of this line segment, which is invariant to the gain factor, is employed for watermarking purpose. We embed the watermarking code by projecting the line segment on some specific lines according to message bits. To design a maximum likelihood decoder, we compute the distribution of the slope of the embedding line segment for Gaussian samples. The performance of the proposed technique is analytically investigated and verified via several simulations. Experimental results confirm the validity of our model and its high robustness against common attacks in comparison with similar watermarking techniques that are invariant to the gain attack.