Masking Functions Research Articles

Cytotoxic Spiroepoxide Lactone and Its Putative Biosynthetic Precursor from Goniobranchus Splendidus.

Epoxygoniolide-1 (1), possessing spiroepoxide lactone, enal, and masked dialdehyde functionalities, has been characterized from the conspicuously patterned mollusc Goniobranchus splendidus. Its relative configuration was investigated by spectroscopic analyses, molecular modeling, and density functional theory calculations. The biosynthesis of 1 may involve rearrangement of a diterpene framework, providing a precursor to cometabolite gonioline (2), followed by C–C bond cleavage (via Grob or P450 mechanism). Moderate cytotoxicity to NCIH-460, SW60, or HepG2 cancer cells was observed for norditerpene 1.

Invisible noise obscures visible signal in insect motion detection

The motion energy model is the standard account of motion detection in animals from beetles to humans. Despite this common basis, we show here that a difference in the early stages of visual processing between mammals and insects leads this model to make radically different behavioural predictions. In insects, early filtering is spatially lowpass, which makes the surprising prediction that motion detection can be impaired by “invisible” noise, i.e. noise at a spatial frequency that elicits no response when presented on its own as a signal. We confirm this prediction using the optomotor response of praying mantis Sphodromantis lineola. This does not occur in mammals, where spatially bandpass early filtering means that linear systems techniques, such as deriving channel sensitivity from masking functions, remain approximately valid. Counter-intuitive effects such as masking by invisible noise may occur in neural circuits wherever a nonlinearity is followed by a difference operation.

Objective determination of backward masking

Backward Masking (BM) functions have been shown to relate to age, lead toxicity, and are differentiated in children with language disorders. These functions may be indicative of auditory processing deficits. This study investigated if Evoked Potentials (EP) could be utilized to obtain BM functions. A tonal stimulus, followed by an inter-stimulus interval (ISI) and a noise masker was the EP stimulus. All were studied individually in the appropriate temporal alignment. ISI”s of various durations to derive the BM function middle, and late auditory evoked potentials. This study randomly presented four different stimulus conditions, 1) tone alone, 2) noise alone, 3) tone and noise, and 4) silence. With a long inter-trial interval (1 sec) and high sample rate (31250 Hz) EP’s were obtained for 4000 trials. The stimuli were pure-tones (1000 Hz, 10 msec. duration with a Blackman function and noise bursts of varying intensity. Agreement was found for the behavioral and electrophysiological task. Results indicated t...

Revealing information by averaging.

We present a method for hiding images in synthetic videos and reveal them by temporal averaging. The main challenge is to develop a visual masking method that hides the input image both spatially and temporally. Our masking approach consists of temporal and spatial pixel by pixel variations of the frequency band coefficients representing the image to be hidden. These variations ensure that the target image remains invisible both in the spatial and the temporal domains. In addition, by applying a temporal masking function derived from a dither matrix, we allow the video to carry a visible message that is different from the hidden image. The image hidden in the video can be revealed by software averaging, or with a camera, by long-exposure photography. The presented work may find applications in the secure transmission of digital information.

Cloud detection algorithm comparison and validation for operational Landsat data products

Clouds are a pervasive and unavoidable issue in satellite-borne optical imagery. Accurate, well-documented, and automated cloud detection algorithms are necessary to effectively leverage large collections of remotely sensed data. The Landsat project is uniquely suited for comparative validation of cloud assessment algorithms because the modular architecture of the Landsat ground system allows for quick evaluation of new code, and because Landsat has the most comprehensive manual truth masks of any current satellite data archive. Currently, the Landsat Level-1 Product Generation System (LPGS) uses separate algorithms for determining clouds, cirrus clouds, and snow and/or ice probability on a per-pixel basis. With more bands onboard the Landsat 8 Operational Land Imager (OLI)/Thermal Infrared Sensor (TIRS) satellite, and a greater number of cloud masking algorithms, the U.S. Geological Survey (USGS) is replacing the current cloud masking workflow with a more robust algorithm that is capable of working across multiple Landsat sensors with minimal modification. Because of the inherent error from stray light and intermittent data availability of TIRS, these algorithms need to operate both with and without thermal data. In this study, we created a workflow to evaluate cloud and cloud shadow masking algorithms using cloud validation masks manually derived from both Landsat 7 Enhanced Thematic Mapper Plus (ETM+) and Landsat 8 OLI/TIRS data. We created a new validation dataset consisting of 96 Landsat 8 scenes, representing different biomes and proportions of cloud cover. We evaluated algorithm performance by overall accuracy, omission error, and commission error for both cloud and cloud shadow. We found that CFMask, C code based on the Function of Mask (Fmask) algorithm, and its confidence bands have the best overall accuracy among the many algorithms tested using our validation data. The Artificial Thermal-Automated Cloud Cover Algorithm (AT-ACCA) is the most accurate nonthermal-based algorithm. We give preference to CFMask for operational cloud and cloud shadow detection, as it is derived from a priori knowledge of physical phenomena and is operable without geographic restriction, making it useful for current and future land imaging missions without having to be retrained in a machine-learning environment.

Auditory Time-Frequency Masking for Spectrally and Temporally Maximally-Compact Stimuli.

Many audio applications perform perception-based time-frequency (TF) analysis by decomposing sounds into a set of functions with good TF localization (i.e. with a small essential support in the TF domain) using TF transforms and applying psychoacoustic models of auditory masking to the transform coefficients. To accurately predict masking interactions between coefficients, the TF properties of the model should match those of the transform. This involves having masking data for stimuli with good TF localization. However, little is known about TF masking for mathematically well-localized signals. Most existing masking studies used stimuli that are broad in time and/or frequency and few studies involved TF conditions. Consequently, the present study had two goals. The first was to collect TF masking data for well-localized stimuli in humans. Masker and target were 10-ms Gaussian-shaped sinusoids with a bandwidth of approximately one critical band. The overall pattern of results is qualitatively similar to existing data for long maskers. To facilitate implementation in audio processing algorithms, a dataset provides the measured TF masking function. The second goal was to assess the potential effect of auditory efferents on TF masking using a modeling approach. The temporal window model of masking was used to predict present and existing data in two configurations: (1) with standard model parameters (i.e. without efferents), (2) with cochlear gain reduction to simulate the activation of efferents. The ability of the model to predict the present data was quite good with the standard configuration but highly degraded with gain reduction. Conversely, the ability of the model to predict existing data for long maskers was better with than without gain reduction. Overall, the model predictions suggest that TF masking can be affected by efferent (or other) effects that reduce cochlear gain. Such effects were avoided in the experiment of this study by using maximally-compact stimuli.

Extended reliability measures for the fast method of schroeder-phase masking

Introduction: Schroeder-phase masking test has been found to be highly useful in providing information on the cochlea phase response that was not previously discovered. Conventional Three Alternative Forced Choice (3AFC) method of conducting Schroeder phase masking takes a long testing time (around 45 minutes) and could possibly limit the valuable information that may be gathered from this test. A faster Schroeder-phase masking method which is able to cut down almost 80% of the testing time has been developed, and has been proven reliable for normal hearing population. This study aims to extend the reliability measures to hearing impaired population. Methods: This is an observational study involving 10 normal hearing and 6 sensorineural hearing loss subjects. Schroeder phase masking functions were measured at 500 Hz, 1 kHz and 2 kHz (75 dB A) using the conventional and fast methods to find the agreement between two methods. The fast method was measured in two sessions to find the test–retest reliability. Results: The fast method showed; i) good agreement with the conventional 3 AFC method-no significant difference of masked thresholds between two methods at majority of the tested conditions (p>0.05), ii) good test retest reliability- no significant difference of masked thresholds between two sessions (p>0.05). Conclusions: Proven to be a reliable method in both normal hearing and hearing impaired population, the faster method could potentially facilitate more Schroeder phase masking experiments in investigating the fundamental of sound processing and auditory perception.

Dichoptic Metacontrast Masking Functions to Infer Transmission Delay in Optic Neuritis.

Optic neuritis (ON) has detrimental effects on the transmission of neuronal signals generated at the earliest stages of visual information processing. The amount, as well as the speed of transmitted visual signals is impaired. Measurements of visual evoked potentials (VEP) are often implemented in clinical routine. However, the specificity of VEPs is limited because multiple cortical areas are involved in the generation of P1 potentials, including feedback signals from higher cortical areas. Here, we show that dichoptic metacontrast masking can be used to estimate the temporal delay caused by ON. A group of 15 patients with unilateral ON, nine of which had sufficient visual acuity and volunteered to participate, and a group of healthy control subjects (N = 8) were presented with flashes of gray disks to one eye and flashes of gray annuli to the corresponding retinal location of the other eye. By asking subjects to report the subjective visibility of the target (i.e. the disk) while varying the stimulus onset asynchrony (SOA) between disk and annulus, we obtained typical U-shaped masking functions. From these functions we inferred the critical SOAmax at which the mask (i.e. the annulus) optimally suppressed the visibility of the target. ON-associated transmission delay was estimated by comparing the SOAmax between conditions in which the disk had been presented to the affected and the mask to the other eye, and vice versa. SOAmax differed on average by 28 ms, suggesting a reduction in transmission speed in the affected eye. Compared to previously reported methods assessing perceptual consequences of altered neuronal transmission speed the presented method is more accurate as it is not limited by the observers’ ability to judge subtle variations in perceived synchrony.

Behavioral and electrophysiological evidence for backward masking

Backward Masking (BM) functions have been shown to relate to age, lead toxicity, and are differentiated in children with language disorders. These functions may be indicative of auditory processing deficits. This study compared BM functions obtained from Evoked Potentials (EP) to behaviorally obtained functions. A stimulus followed by an ISI and a noise masker were presented. All were studied individually in the appropriate temporal alignment. The design of this study allowed observation of the early, middle, and late auditory evoked potentials. For the behavioral task, stimuli were presented with a method of adjustment. This study randomly presented four different stimulus conditions: 1) stimulus alone, 2) noise alone, 3) stimulus and noise, and 4) silence. With a long inter-trial interval (1 s) and high sample rate (25,600 Hz) EP’s were obtained for 4000 trials. The stimuli were pure-tones (1000 Hz, 10 ms duration with a Blackman function and brief 100 microsecond clicks of varying intensity and varied ...

Blind image counterwatermarking \u2013 hidden data filter

Watermarking is a dynamically developing method of copyright protection used for media (sounds, images, films, or 3D objects) that employs signal processing in order to hide additional, invisible information about the owner or author. However, studies until now have not widely considered the problem of attempting to blind removal of hidden data in a manner that allows the watermarked signal to be returned to the original signal. Current considerations of authors of leading articles in the watemarking field focus on the robustness of the method – security system against intentional attacks of removal of the additional information, without taking into account the aspect of simultaneous degradation of the quality and form of the watermarked picture. As has been shown in the article, it is possible to design a perfect filter (same as reversible operations) that allows the removal of additional information from the watermarked picture in a way that makes it possible to return to the form of the host image. This paper describes an ideal filter used for removal of additional, invisible information in forms of an eliminating function and a signal masking function. Their effectiveness has been demonstrated for practical implementations of this type of eliminating and masking filters for watermarking methods in the cepstrum domain.

Unmasked chronic renal function deterioration after unilateral adrenalectomy in patients with primary aldosteronism

We report 2 cases of chronic estimated glomerular filtration rate (eGFR) decline after unilateral adrenalectomy due to primary aldosteronism. The patients were diagnosed with unilateral adrenal cortical adenoma releasing aldosterone. Two patients were examined for hypertension and hypokalemia. Unilateral laparoscopic adrenalectomy was performed in both cases, and pathology confirmed adrenal cortical adenoma. After adrenalectomy, hypertension and hypokalemia improved to within normal range. However, the eGFR decreased postoperatively, and abdominal computed tomography scan showed decreased kidney size compared to previous images. Kidney biopsy was performed to delineate the exact cause of renal function deterioration and revealed hypertensive changes with chronic interstitial changes, indicating that glomerular hyperfiltration with aldosterone excess masked renal function damage. Physicians have to consider the probability of postadrenalectomy eGFR decline related to chronic hypertensive change.

Nanoscopic characterization of immunogenic b-glucan exposure on Candida species pathogens

Abstract The cell walls of Candida spp. are composed largely of polysaccharides. Here we focus on β-glucan, an immunogenic cell wall polysaccharide whose surface exposure is masked from the innate immunoreceptor Dectin-1 to evade immunity. Previous research suggested that the physical presentation geometry of β-glucan may determine whether or not it can be recognized by Dectin-1. We used super resolution imaging to measure the fine structure of glucan exposure on C. albicans cell walls before and after glucan unmasking with the antimycotic drug caspofungin. Most exposed glucan on C. albicans yeast and hyphae exists as single Dectin-1 binding sites. Caspofungin-mediated glucan unmasking results in nanoscale remodeling of glucan exposures, resulting in increased density and size of glucan exposure sites. The less studied pathogen C. glabrata exhibits significantly greater glucan exposure than C. albicans in type strains, but recent clinical isolates of C. glabrata have lower exposure, suggesting that C. glabrata also masks its glucan. We used C. glabrata cell wall mutants to define the role of N-mannan structure in maintaining glucan masking. The less complex N-mannan structures of mutant strains provided poorer glucan masking, increasing the density of nanoscale glucan exposure sites. a-(1,6)-mannan backbone length was a major structural determinant of glucan masking, while a-(1,2;1,3)-mannan side chain density was less critical to masking function. This work provides the first characterization of changing glucan exposure nanostructure at the pathogenic cell wall surface that participates in host-Candida interaction. Further studies will examine the functional impact of glucan nanostructure on Dectin-1 activation.

The Eng1 β-Glucanase Enhances Histoplasma Virulence by Reducing β-Glucan Exposure.

ABSTRACTThe fungal pathogen Histoplasma capsulatum parasitizes host phagocytes. To avoid antimicrobial immune responses, Histoplasma yeasts must minimize their detection by host receptors while simultaneously interacting with the phagocyte. Pathogenic Histoplasma yeast cells, but not avirulent mycelial cells, secrete the Eng1 protein, which is a member of the glycosylhydrolase 81 (GH81) family. We show that Histoplasma Eng1 is a glucanase that hydrolyzes β-(1,3)-glycosyl linkages but is not required for Histoplasma growth in vitro or for cell separation. However, Histoplasma yeasts lacking Eng1 function have attenuated virulence in vivo, particularly during the cell-mediated immunity stage. Histoplasma yeasts deficient for Eng1 show increased exposure of cell wall β-glucans, which results in enhanced binding to the Dectin-1 β-glucan receptor. Consistent with this, Eng1-deficient yeasts trigger increased tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) cytokine production from macrophages and dendritic cells. While not responsible for large-scale cell wall structure and function, the secreted Eng1 reduces levels of exposed β-glucans at the yeast cell wall, thereby diminishing potential recognition by Dectin-1 and proinflammatory cytokine production by phagocytes. In α-glucan-producing Histoplasma strains, Eng1 acts in concert with α-glucan to minimize β-glucan exposure: α-glucan provides a masking function by covering the β-glucan-rich cell wall, while Eng1 removes any remaining exposed β-glucans. Thus, Histoplasma Eng1 has evolved a specialized pathogenesis function to remove exposed β-glucans, thereby enhancing the ability of yeasts to escape detection by host phagocytes.

Backward masking determination with simultaneous early, middle, and late evoked potentials

Backward masking (BM) functions have been shown to relate to age, lead toxicity, and are differentiated in children with language disorders. These functions may be indicative of auditory processing deficits. This study investigated if evoked potentials (EP) could be utilized to obtain BM functions. A tonal stimulus, followed by an ISI and a noise masker was the EP stimulus. All were studied individually in the appropriate temporal alignment. The design of this study allowed observation of the early, middle, and late auditory evoked potentials. This study randomly presented four different stimulus conditions: (1) tone alone, (2) noise alone, (3) tone and noise, and (4) silence. With a long inter-trial interval (1 s) and high sample rate (25 600 Hz) EP’s were obtained for 4000 trials. The stimuli were pure-tones (1000 Hz, 10 ms duration with a Blackman function and noise bursts of varying intensity and varied ISI. Results indicated that EP’s could be arithmetically combined to observe the differential electrophysiological responses and neurologic loci of evoked potentials during the BM effect.

Comparison of Blackman, linear rise-fall, and linear rise-fall chirp signals in backward masking

Backward masking is finding applications in clinical testing and the diagnosis of auditory processing disorders. Masking of a tonal signal by a band-limited noise in a backward masking paradigm requires significant vigilance and produces fatigue. This study compared the backward masking functions of ten normal hearing young (18–30 years) subjects using tonal stimuli with different signatures in order to provide a better contrast to the noise masker. Subjects adaptively tracked the tonal threshold using 2 dB changes. The noise stimulus was 70 dB HL, and the inter-stimulus interval (ISI) varied from 2 ms to 64 ms. The results will be described in terms of fatigue, tracking efficiency, and latency.

Individually different weighting of multiple processes underlies effects of metacontrast masking.

Metacontrast masking occurs when a mask follows a target stimulus in close spatial proximity. Target visibility varies with stimulus onset asynchrony (SOA) between target and mask in individually different ways leading to different masking functions with corresponding phenomenological reports. We used individual differences to determine the processes that underlie metacontrast masking. We assessed individual masking functions in a masked target discrimination task using different masking conditions and applied factor-analytical techniques on measures of sensitivity. Results yielded two latent variables that (1) contribute to performance with short and long SOA, respectively, (2) relate to specific stimulus features, and (3) differentially correlate with specific subjective percepts. We propose that each latent variable reflects a specific process. Two additional processes may contribute to performance with short and long SOAs, respectively. Discrimination performance in metacontrast masking results from individually different weightings of two to four processes, each of which contributes to specific subjective percepts.

Performance of circularly masked planar arrays

In this paper, the two-dimensional planar array is designed to reduce the sidelobe levels without any extra processing for the feeding currents or changing the elements locations. The design will trim the elements at the four corners with a specific circular masking function which results in a redistribution of the sidelobes so that the two major planes of sidelobes at θ=0 and 90 degrees are reduced at the cost of increasing other negligible sidelobes. The new masked two-dimensional array has the advantage of easier manufacturing over the concentric circular arrays while maintaining almost the same sidelobe levels and patterns. The analysis of the proposed array design shows that the sidelobe levels will be reduced by 4dB at first sidelobe in the two major sidelobe planes and is more reduced by up to 10dB at other sidelobes without any processing or change in the feeding currents. In addition, the sidelobe levels can be further reduced by applying amplitude window functions such as the Hamming window in conjunction with the masking which will reduce greatly the sidelobes level to greater than 30dB below the main lobe level.

Thermotriggered Catalyst-Free Modification of a Glass Surface with an Orthogonal Agent Possessing Nitrile N-Oxide and Masked Ketene Functions.

The thermotriggered modification of surfaces was performed under catalyst-free conditions using an orthogonal agent possessing both nitrile N-oxide and Meldrum's acid moieties. The nitrile N-oxide moiety of the orthogonal agent successfully underwent catalyst-free 1,3-dipolar cycloaddition to unsaturated bonds of glass surfaces to produce Meldrum's acid-functionalized surfaces. The subsequent thermal decomposition of Meldrum's acid moiety in the presence of nucleophiles afforded versatile nucleophile-modified surfaces (e.g., wet, waterproof, and photoactive surfaces). Surface characteristics were investigated with the water contact angle, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS). In addition, the surface modification of silica nanoparticles using the orthogonal agent was also achieved to evaluate the density of the functional group concentration on the surface.

Selective Inner Hair Cell Dysfunction in Chinchillas Impairs Hearing-in-Noise in the Absence of Outer Hair Cell Loss.

Poorer hearing in the presence of background noise is a significant problem for the hearing impaired. Ototoxic drugs, ageing, and noise exposure can damage the sensory hair cells of the inner ear that are essential for normal hearing sensitivity. The relationship between outer hair cell (OHC) loss and progressively poorer hearing sensitivity in quiet or in competing background noise is supported by a number of human and animal studies. In contrast, the effect of moderate inner hair cell (IHC) loss or dysfunction shows almost no impact on behavioral measures of hearing sensitivity in quiet, when OHCs remain intact, but the relationship between selective IHC loss and hearing in noise remains relatively unknown. Here, a moderately high dose of carboplatin (75mg/kg) that produced IHC loss in chinchillas ranging from 40 to 80% had little effect on thresholds in quiet. However, when tested in the presence of competing broadband (BBN) or narrowband noise (NBN), thresholds increased significantly. IHC loss >60% increased signal-to-noise ratios (SNRs) for tones (500-11,300Hz) in competing BBN by 5-10dB and broadened the masking function under NBN. These data suggest that IHC loss or dysfunction may play a significant role in listening in noise independent of OHC integrity and that these deficits may be present even when thresholds in quiet are within normal limits.

Joint Optimization of Masks and Deep Recurrent Neural Networks for Monaural Source Separation

Monaural source separation is important for many real world applications. It is challenging because, with only a single channel of information available, without any constraints, an infinite number of solutions are possible. In this paper, we explore joint optimization of masking functions and deep recurrent neural networks for monaural source separation tasks, including monaural speech separation, monaural singing voice separation, and speech denoising. The joint optimization of the deep recurrent neural networks with an extra masking layer enforces a reconstruction constraint. Moreover, we explore a discriminative criterion for training neural networks to further enhance the separation performance. We evaluate the proposed system on the TSP, MIR-1K, and TIMIT datasets for speech separation, singing voice separation, and speech denoising tasks, respectively. Our approaches achieve 2.30--4.98 dB SDR gain compared to NMF models in the speech separation task, 2.30--2.48 dB GNSDR gain and 4.32--5.42 dB GSIR gain compared to existing models in the singing voice separation task, and outperform NMF and DNN baselines in the speech denoising task.