Multichannel Advantage Research Articles

A Spatial-Channel Collaborative Attention Network for Enhancement of Multiresolution Classification

Recently, with the popularity of space-borne earth satellites, the resolution of high-resolution panchromatic (PAN) and multispectral (MS) remote sensing images is also increasing year by year, multiresolution remote sensing classification has become a research hotspot. In this paper, from the perspective of deep learning, we design a dual-branch interactive spatial-channel collaborative attention enhancement network (SCCA-net) for multiresolution classification. It aims to combine sample enhancement and feature enhancement to improve classification accuracy. In the part of sample enhancement, we propose an adaptive neighbourhood transfer sampling strategy (ANTSS). Different from the traditional pixel-centric sampling strategy with orthogonal sampling angle, our algorithm allows each patch to adaptively transfer the neighbourhood range by finding the homogeneous region of the pixel to be classified. And it also adaptively adjust the sampling angle according to the texture distribution of the homogeneous region to capture neighbourhood information that is more conducive for classification. Moreover, in the part of feature enhancement part, we design a local spatial attention module (LSA-module) for PAN data to highlight the spatial resolution advantages and a global channel attention module (GCA-module) for MS data to improve the multi-channel representation. It not only highlights the spatial resolution advantage of PAN data and the multi-channel advantage of MS data, but also improves the difference between features through the interaction between the two modules. Quantitative and qualitative experimental results verify the robustness and effectiveness of the method.

Envelope Interactions in Multi-Channel Amplitude Modulation Frequency Discrimination by Cochlear Implant Users.

RationalePrevious cochlear implant (CI) studies have shown that single-channel amplitude modulation frequency discrimination (AMFD) can be improved when coherent modulation is delivered to additional channels. It is unclear whether the multi-channel advantage is due to increased loudness, multiple envelope representations, or to component channels with better temporal processing. Measuring envelope interference may shed light on how modulated channels can be combined.MethodsIn this study, multi-channel AMFD was measured in CI subjects using a 3-alternative forced-choice, non-adaptive procedure (“which interval is different?”). For the reference stimulus, the reference AM (100 Hz) was delivered to all 3 channels. For the probe stimulus, the target AM (101, 102, 104, 108, 116, 132, 164, 228, or 256 Hz) was delivered to 1 of 3 channels, and the reference AM (100 Hz) delivered to the other 2 channels. The spacing between electrodes was varied to be wide or narrow to test different degrees of channel interaction.ResultsResults showed that CI subjects were highly sensitive to interactions between the reference and target envelopes. However, performance was non-monotonic as a function of target AM frequency. For the wide spacing, there was significantly less envelope interaction when the target AM was delivered to the basal channel. For the narrow spacing, there was no effect of target AM channel. The present data were also compared to a related previous study in which the target AM was delivered to a single channel or to all 3 channels. AMFD was much better with multiple than with single channels whether the target AM was delivered to 1 of 3 or to all 3 channels. For very small differences between the reference and target AM frequencies (2–4 Hz), there was often greater sensitivity when the target AM was delivered to 1 of 3 channels versus all 3 channels, especially for narrowly spaced electrodes.ConclusionsBesides the increased loudness, the present results also suggest that multiple envelope representations may contribute to the multi-channel advantage observed in previous AMFD studies. The different patterns of results for the wide and narrow spacing suggest a peripheral contribution to multi-channel temporal processing. Because the effect of target AM frequency was non-monotonic in this study, adaptive procedures may not be suitable to measure AMFD thresholds with interfering envelopes. Envelope interactions among multiple channels may be quite complex, depending on the envelope information presented to each channel and the relative independence of the stimulated channels.

Modulation frequency discrimination with single and multiple channels in cochlear implant users

Temporal envelope cues convey important speech information for cochlear implant (CI) users. Many studies have explored CI users' single-channel temporal envelope processing. However, in clinical CI speech processors, temporal envelope information is processed by multiple channels. Previous studies have shown that amplitude modulation frequency discrimination (AMFD) thresholds are better when temporal envelopes are delivered to multiple rather than single channels. In clinical fitting, current levels on single channels must often be reduced to accommodate multi-channel loudness summation. As such, it is unclear whether the multi-channel advantage in AMFD observed in previous studies was due to coherent envelope information distributed across the cochlea or to greater loudness associated with multi-channel stimulation. In this study, single- and multi-channel AMFD thresholds were measured in CI users. Multi-channel component electrodes were either widely or narrowly spaced to vary the degree of overlap between neural populations. The reference amplitude modulation (AM) frequency was 100 Hz, and coherent modulation was applied to all channels. In Experiment 1, single- and multi-channel AMFD thresholds were measured at similar loudness. In this case, current levels on component channels were higher for single-than for multi-channel AM stimuli, and the modulation depth was approximately 100% of the perceptual dynamic range (i.e., between threshold and maximum acceptable loudness). Results showed no significant difference in AMFD thresholds between similarly loud single- and multi-channel modulated stimuli. In Experiment 2, single- and multi-channel AMFD thresholds were compared at substantially different loudness. In this case, current levels on component channels were the same for single- and multi-channel stimuli (“summation-adjusted” current levels) and the same range of modulation (in dB) was applied to the component channels for both single- and multi-channel testing. With the summation-adjusted current levels, loudness was lower with single than with multiple channels and the AM depth resulted in substantial stimulation below single-channel audibility, thereby reducing the perceptual range of AM. Results showed that AMFD thresholds were significantly better with multiple channels than with any of the single component channels. There was no significant effect of the distribution of electrodes on multi-channel AMFD thresholds. The results suggest that increased loudness due to multi-channel summation may contribute to the multi-channel advantage in AMFD, and that overall loudness may matter more than the distribution of envelope information in the cochlea.

Single- and multi-channel modulation detection in cochlear implant users.

Single-channel modulation detection thresholds (MDTs) have been shown to predict cochlear implant (CI) users’ speech performance. However, little is known about multi-channel modulation sensitivity. Two factors likely contribute to multichannel modulation sensitivity: multichannel loudness summation and the across-site variance in single-channel MDTs. In this study, single- and multi-channel MDTs were measured in 9 CI users at relatively low and high presentation levels and modulation frequencies. Single-channel MDTs were measured at widely spaced electrode locations, and these same channels were used for the multichannel stimuli. Multichannel MDTs were measured twice, with and without adjustment for multichannel loudness summation (i.e., at the same loudness as for the single-channel MDTs or louder). Results showed that the effect of presentation level and modulation frequency were similar for single- and multi-channel MDTs. Multichannel MDTs were significantly poorer than single-channel MDTs when the current levels of the multichannel stimuli were reduced to match the loudness of the single-channel stimuli. This suggests that, at equal loudness, single-channel measures may over-estimate CI users’ multichannel modulation sensitivity. At equal loudness, there was no significant correlation between the amount of multichannel loudness summation and the deficit in multichannel MDTs, relative to the average single-channel MDT. With no loudness compensation, multichannel MDTs were significantly better than the best single-channel MDT. The across-site variance in single-channel MDTs varied substantially across subjects. However, the across-site variance was not correlated with the multichannel advantage over the best single channel. This suggests that CI listeners combined envelope information across channels instead of attending to the best channel.

Integral wide-field spectroscopy in astronomy: the Imaging FTS solution

Long-slit grating spectrometers in scanning mode and Fabry–Perot interferometers as tunable filters are commonly used to perform integral wide-field spectroscopy on extended astrophysical objects as HII regions and nearby galaxies. The goal of this paper is to demonstrate, by comparison, through a thorough review of the imaging Fourier transform spectrometer (IFTS) properties, that this instrument represents another interesting solution. After a brief recall of the performances, regarding FOV and spectral resolution, of the grating spectrometer, without and with integral field units (IFU), and of the imaging Fabry–Perot, it is demonstrated that for an IFTS the product of the maximum resolution R by the entrance beam etendue U is equal to $2.6\,N\times S_I$ with $N\,\times \,N$ the number of pixels of the detector array and S $_I$ the area of the interferometer beamsplitter. As a consequence, the IFTS offers the most flexible choice of field size and spectral resolution, up to high values for both parameters. It also presents on a wide field an important multichannel advantage in comparison to integral field grating spectrometers, even with multiple IFUs. To complete, the few astronomical IFTSs, built behind ground-based telescopes and in space, for the visible range up to the sub-millimetric domain, are presented. Through two wide-field IFTS projects, one in the visible, the other one in the mid-infrared, the question is addressed of the practical FOV and resolution limits, set by the optical design of the instrument, which can be achieved. Within the 0.3 to $\sim $ 2.5 $\upmu$ m domain, a Michelson interferometer with wide-field diopric collimators provides the easiest solution. This design is illustrated by a $11^{\prime}\times 11^{\prime}$ -field IFTS in the 0.35–0.90 $\upmu$ m range around an off-axis interferometer, called SITELLE, proposed for the 3.6-m CFH Telescope. At longer wavelengths, an all-mirror optics is required, as studied for a spaceborne IFTS, H2EX, for the 8–29 $\upmu$ m range, a $20^{\prime} \times 20^{\prime}$ field, and a high resolution of $\simeq 3\times 10^4$ at 10 $\upmu$ m. To comply with these characteristics, the interferometer is designed with cat’s eye retroreflectors. In the same domain and up to the far infrared, if the instrument aims only at a low spectral resolution (few thousands) and a smaller field (few arcmins $^2$ ), roof-top or corner cube mirrors, as for the IFTS SPIRE on the Herschel space telescope, are usable. At last, perspectives are opened, behind an ELT in the visible and the near infrared with the SITELLE optical combination, in the 2–5 $\upmu$ m on the Antarctic plateau or in space up to longer wavelengths, with the H2EX design, to provide the missing capability of global high spectral resolution studies of extended sources, from comets to distant galaxy clusters.

Variable-weighted PLS

In multivariate calibration methods like partial least squares (PLS), especially when the spectra data consists of measurements at hundreds and even thousands of analytical channels, it is widely accepted that before a multivariate regression model is built, a well-performed variable selection can be helpful to improve the predictive ability of the model. In the present paper, the idea of variable selection is extended. Unlike in traditional variable selection methods, where the deleted variables and the variables included in the regression model are essentially weighted with discrete values 0 and 1, respectively, the strategy adopted in this paper is to weight the variables with continuous non-negative values. A recently proposed global optimization method, particle swarm optimization (PSO) algorithm is used to search for the weights of variables optimizing the training of a calibration set and the prediction of an independent validation set. Since variable selection is just a special case of variable weighting, the latter is expected to be more rational and flexible. Variable weighting would reduce the negative influence of wavelengths with undesirable qualities while retaining the useful information carried by them. Variable weighting would also prevent the possible spoiling of the multi-channel advantage of the model by variable selection, which would happen when the number of selected wavelengths is small. Two real data sets are investigated and the results of variable-weighted PLS and those of PLS are compared to demonstrate the advantages of the proposed method.

Enhanced Time-Resolved Fourier Transform Infrared Spectroscopic Imaging for Reversible Dynamics

Time-resolved (TR) Fourier transform infrared (FTIR) spectroscopic imaging provides noninvasively spatial and spectral observations of molecular dynamic processes in heterogeneous environments. The technique, however, is limited by the readout time of the imaging focal plane array detector due to a tradeoff between the multichannel detection advantage and the achievable temporal resolution. We describe a generalized implementation of TR-FTIR spectroscopic imaging that, without affecting data quality, allows potential measurements of up to 2 orders of magnitude greater in time resolution than previously reported; that is, time resolutions of milliseconds to tenths of milliseconds are achievable for reversible dynamic processes. As an example, molecular rotations occurring in embedded liquid crystalline microdomains are monitored with a 2.5 ms time resolution allowing an accurate determination of events inherent in the reorientation and relaxation processes.

Precision and Noise in Inductively Coupled Plasma Atomic Emission Spectroscopy with Charge-Injection Device Detection

An inductively coupled plasma (ICP)-echelle optical system coupled with a charge-injection device (CID) detector was evaluated for precision and noise. Simultaneous collection of analyte wavelengths and simultaneous background correction have invalidated underlying assumptions in some traditional models. Signal flicker noise, a major limitation in single-channel detection, was eliminated by the time correlation of analyte and internal standard wavelengths. Once flicker noise was eliminated, most fluctuation was found to be caused by slight wavelength shifts along the axis of the detector, rather than by the theoretically predicted signal shot noise. This fluctuation can be corrected by increasing center subarray sizes or by employing well-matched internal standard lines. In either case, precision of 0.3 to 0.18% relative standard deviation (RSD) was achieved over a time span of 7 h. Background flicker noise was also eliminated by simultaneous background correction, demonstrating a multichannel advantage of ICP detection using charge-transfer devices. In this work, theoretical expressions were developed to incorporate major sources of noise based on the specific readout characteristics of an array detector. These expressions match experimental data extremely well for measurement of relative standard deviation in background (RSDB) and detection limits. These data have then been compared to the single-channel case, which describes photomultiplier tube (PMT) detection, as well as the theoretical limit dictated by background shot noise.

Construction of Electric-Field-Modulated Picosecond Time-Resolved Fluorescence Spectrometer

We have developed a new electric-field-modulated picosecond time-resolved fluorescence spectrometer using a streak scope. We can obtain an electric-field-induced change of a fluorescence lifetime and that of an amplitude as low as 1% without losing the two-dimensional multichannel advantage of the streak scope. The spectrometer enabled us to observe electric-field-induced fluorescence quenching of titanyl phthalocyanine and obtain valuable information on the mechanism of photocarrier generation.

FT-IR Spectroscopic Imaging in the Infrared “Fingerprint”Region Using an Mct Array Detector

Abstract A new infrared spectroscopic imaging technique has been described, combining step-scan Fourier transform (FT) Michelson interferometry with indium antimonide (InSb) focal-plane array (FPA) image detection [1-3], for use in the range 3950-1975 cm−1. The coupling of such detector to an interferometer provides an optimized method for infrared spectroscopic imaging by simultaneously realizing both a multiplex and multichannel advantage. Specifically, the multiple detector elements enable spectra at all pixels to be collected simultaneously, while the interferometer allows all the spectral frequencies to be measured concurrently. This technique can rapidly generate very high quality, chemically specific images from a wide variety of samples. Preliminary results from the use of a mid-infrared liquid-helium-cooled arsenic-doped-silicon array have also been reported recently [4]. Focal-plane arrays using mercury-cadmium-telluride (MCT) are now commercially available, giving access to the range 3950-800 cm−1, and greatly broadening the applicability of this technique [5]. FT-IR microscopy does not require exotic sample preparation -- samples can be examined in transmission and reflectance, do not need to be stained or coated, and a vacuum is not required.

Si: As Focal-Plane Array Detection for Fourier Transform Spectroscopic Imaging in the Infrared Fingerprint Region

An instrument is described that simultaneously records images and spectra of materials in the infrared fingerprint region using a long-wavelength infrared focal-plane array detector, a step-scan Michelson interferometer, and an infrared microscope. With the combination of step-scan Fourier transform (FT) Michelson interferometry and arsenic-doped silicon (Si: As) focal-plane array image detection, an infrared spectroscopic imaging system has been constructed that maintains both an instrumental multiplex and multichannel advantage and operates from approximately 4000 to 400 cm−1. With this method of mid-infrared spectroscopic imaging, the fidelity of the generated spectral images recorded through the microscope is solely determined by the number of pixels on the focal-plane array detector, and only a few seconds of data acquisition time are required for spectral image acquisition. This seamless combination of spectroscopy for molecular analysis and the power of visualization represents the future of infrared microscopy. Step-scan imaging principles, the operation and characteristics of long-wavelength array detectors, and instrument design details are outlined, and infrared chemical imaging results are presented. The results are discussed with respect to their implications for the chemical analysis of a variety of solid-state materials.

High-Fidelity Raman Imaging Spectrometry: A Rapid Method Using an Acousto-Optic Tunable Filter

In this communication, we describe a technique for obtaining high-fidelity Raman images and Raman spectra. The instrumentation provides the ability to rapidly collect large-format images with the number of image pixels limited only by the number of detector elements in the silicon charge-coupled device (CCD). Wavelength selection is achieved with an acousto-optic tunable filter (AOTF), which maintains image fidelity while providing spectral selectivity. Under computer control the AOTF is capable of µs tuning speeds within the operating range of the filter (400–1900 nm). The AOTF is integrated with the CCD and holographic Raman filters to comprise an entirely solid-state Raman imager containing no moving parts. In operation, the AOTF is placed in front of the CCD and tuned over the desired spectral interval. The two-dimensional CCD detector is employed as a true imaging camera, providing a full multichannel advantage over competitive Raman imaging techniques. Images and spectra are presented of a mixture of dipalmitoylphosphatidylcholine (DPPC) and L-asparagine, which serves as a model system for the study of both lipid/peptide and lipid/protein interactions in intact biological materials. The Raman images are collected in only several seconds and indicate the efficacy of this rapid technique for discriminating between multiple components in complex matrices. Additionally, high-quality Raman spectra of the spatially resolved microscopic regions are easily obtained.

Theoretical signal-to-noise ratio and resolution for the rapid scan technique in ion cyclotron resonance spectroscopy

Analytical expressions are derived for the signal-to-noise ratio and resolution for the rapid scan technique in ion cyclotron resonance spectroscopy. The expressions show essentially the same features as those in the pulsed Fourier transform technique. Both techniques have the multichannel advantage and exhibit a trade-off of signal-to-noise ratio vs. resolution in selecting the observation period; the signal-to-noise ratio increases at short observation periods, while the resolution does so at long observation periods. Another expression is also derived for the error arising from the truncation of the excitation. Finally, a comparison is made of some features in the conventional continuous wave, the pulsed Fourier transform, and the present rapid scan technique.

Fourier transform mass spectrometry.

Fourier transform mass spectrometry will play an important role in the future because of its unique combination of high mass resolution, high upper mass limit, and multichannel advantage. These features have already found application in gas chromatography-mass spectrometry, multiphoton ionization, laser desorption, and secondary ion mass spectrometry. However, its most notable feature is the ability to store ions. This characteristic, when combined with the others, will allow expeditious study of the interaction of gas-phase ions with both photons (photodissociation) and neutral molecules, and the convenient application of this fundamental information for chemical analysis.

Convolution Fourier transform ion cyclotron resonance spectroscopy

This paper reports first use of a numerical deconvolution procedure for producing amplitude-corrected, phase-corrected absorption-mode Fourier transform ion cyclotron resonance (FT ICR) spectra. Compared to magnitude-mode FT ICR spectral display, the new method can enhance mass resolution by a factor of 2, eliminate irregularity in peak heights at different m/e, reduce baseline noise, and eliminate line shape distortions for closely-spaced peaks, while retaining the multichannel advantage of Fourier data reduction.