Noise Carrier Research Articles

Processing deficits of motion of contrast-modulated gratings in anisometropic amblyopia.

Several studies have indicated substantial processing deficits for static second-order stimuli in amblyopia. However, less is known about the perception of second-order moving gratings. To investigate this issue, we measured the contrast sensitivity for second-order (contrast-modulated) moving gratings in seven anisometropic amblyopes and ten normal controls. The measurements were performed with non-equated carriers and a series of equated carriers. For comparison, the sensitivity for first-order motion and static second-order stimuli was also measured. Most of the amblyopic eyes (AEs) showed reduced sensitivity for second-order moving gratings relative to their non-amblyopic eyes (NAEs) and the dominant eyes (CEs) of normal control subjects, even when the detectability of the noise carriers was carefully controlled, suggesting substantial processing deficits of motion of contrast-modulated gratings in anisometropic amblyopia. In contrast, the non-amblyopic eyes of the anisometropic amblyopes were relatively spared. As a group, NAEs showed statistically comparable performance to CEs. We also found that contrast sensitivity for static second-order stimuli was strongly impaired in AEs and part of the NAEs of anisometropic amblyopes, consistent with previous studies. In addition, some amblyopes showed impaired performance in perception of static second-order stimuli but not in that of second-order moving gratings. These results may suggest a dissociation between the processing of static and moving second-order gratings in anisometropic amblyopia.

Inter-carrier Interference Reduction Scheme for SFBC-OFDM Systems

In this paper, we first analyze carrier-to-interference ratio performance of the space-frequency block coded orthogonal frequency-division multiplexing (SFBC-OFDM) system in the presence of phase noise (PHN) and residual carrier frequency offset (RCFO). From the analysis, we observe that conventional SFBC-OFDM systems suffer severely in the presence of PHN and RCFO. Therefore, we propose a new inter-carrier interference (ICI) self-cancellation method - namely, ISC - for SFBC-OFDM systems to reduce the ICI caused by PHN and RCFO. Through the simulation results, we show that the proposed scheme compensates the ICI caused by PHN and RCFO in Alamouti SFBC-OFDM systems and has a better performance than conventional schemes.

Intensity Noise of an Actively Mode-Locked Quantum Dot External Cavity Laser

We present the intensity noise characteristics of an actively mode-locked quantum-dot hybrid soliton pulse source (QD-HSPS) with a linearly chirped Gaussian-apodized fiber Bragg grating. The QD-HSPS is modeled by using an approximate solution for the propagation equation that governs the electric field and the rate equations, including spontaneous and carrier noise sources. Our results show that QD carrier noise is the most effective noise type, and the spontaneous coupling factor, carrier recombination time in the QD, and laser cavity length are the most important noise parameters. In addition we find that a QD-HSPS produces considerably shorter pulses, with or without noise, than a multi-quantum-well HSPS and has a larger mode-locking frequency range.

Linewidth and Noise Characterization for a Partially-Slotted, Single Mode Laser

We present an in-depth analysis of the linewidth of a partially slotted semiconductor laser utilized for single mode operation exhibiting integrability with other photonic devices. Theoretically, the reflection coefficients are calculated via the scattering matrix method and implemented within the multimode rate equations for a current-injected quantum well laser while including the effects of noise. The coupling between photon and carrier noise is included for completeness and explicitly derived in this case. The threshold current and linewidth as a function of injection current and cavity length are then calculated for an optimized slot size. Results show state-of-the-art capabilities for this laser to meet industrial requirements for linewidths well under 500 kHz. In addition, experimental data extracted via a heterodyne detection measurement of the electric field spectrum demonstrates similar trends with our theoretical calculations.

Spectrum Sensing Based on Time-frequency Dispersion Analysis

A novel spectrum sensing algorithm is proposed based on time-frequency dispersion analysis. Timefrequency ridge line is flrstly calculated of a received data’s mutual correlation to form a series of timefrequency dots. Time-frequency dispersion function is subsequently deflned to describe the dispersion level of the time-frequency dots according to the fact that signal energy gather around the carrier frequency and noise energy disperse evenly among all frequencies. And the dispersion threshold is set to make an existence decision of primary user’s signal. Simulations indicates: the time-frequency dispersion is robust to noise power uncertainty, receiver’s bandwidth and behaves stability with enough data length; the proposed algorithm is efiective both for normal and fading channel and maintains good detecting performance at lower SNRs.

Age-related changes in the relationship between auditory brainstem responses and envelope-following responses.

Hearing thresholds and wave amplitudes measured using auditory brainstem responses (ABRs) to brief sounds are the predominantly used clinical measures to objectively assess auditory function. However, frequency-following responses (FFRs) to tonal carriers and to the modulation envelope (envelope-following responses or EFRs) to longer and spectro-temporally modulated stimuli are rapidly gaining prominence as a measure of complex sound processing in the brainstem and midbrain. In spite of numerous studies reporting changes in hearing thresholds, ABR wave amplitudes, and the FFRs and EFRs under neurodegenerative conditions, including aging, the relationships between these metrics are not clearly understood. In this study, the relationships between ABR thresholds, ABR wave amplitudes, and EFRs are explored in a rodent model of aging. ABRs to broadband click stimuli and EFRs to sinusoidally amplitude-modulated noise carriers were measured in young (3-6months) and aged (22-25months) Fischer-344 rats. ABR thresholds and amplitudes of the different waves as well as phase-locking amplitudes of EFRs were calculated. Age-related differences were observed in all these measures, primarily as increases in ABR thresholds and decreases in ABR wave amplitudes and EFR phase-locking capacity. There were no observed correlations between the ABR thresholds and the ABR wave amplitudes. Significant correlations between the EFR amplitudes and ABR wave amplitudes were observed across a range of modulation frequencies in the young. However, no such significant correlations were found in the aged. The aged click ABR amplitudes were found to be lower than would be predicted using a linear regression model of the young, suggesting altered gain mechanisms in the relationship between ABRs and FFRs with age. These results suggest that ABR thresholds, ABR wave amplitudes, and EFRs measure complementary aspects of overlapping neurophysiological processes and the relationships between these measurements changes asymmetrically with age. Hence, measuring all three metrics provides a more complete assessment of auditory function, especially under pathological conditions like aging.

Joint Iterative Carrier Synchronization and Signal Detection Employing Expectation Maximization

In this paper, joint estimation of carrier frequency, phase, signal means and noise variance, in a maximum likelihood sense, is performed iteratively by employing expectation maximization. The parameter estimation is soft decision driven and allows joint carrier synchronization and data detection. The algorithm is tested in a mixed line rate optical transmission scenario employing dual polarization 448 Gb/s 16-QAM signal surrounded by eight on-off keying channels in a 50 GHz grid. It is shown that joint carrier synchronization and data detection are more robust towards optical transmitter impairments and nonlinear phase noise, compared to digital phase-locked loop (PLL) followed by hard decisions. Additionally, soft decision driven joint carrier synchronization and detection offers an improvement of 0.5 dB in terms of input power compared to hard decision digital PLL based carrier synchronization and demodulation.

Low noise optical multi-carrier generation using optical-FIR filter for ASE noise suppression in re-circulating frequency shifter loop

In this paper, an improved multi-carrier generation scheme based on single-side-band recirculating frequency shifter with optical finite impulse response (FIR) filter for amplified spontaneous emission (ASE) noise suppression is proposed and experimentally demonstrated. The carrier-to-noise-ratio (CNR) instead of tone-to-noise-ratio (TNR) is introduced to more reasonably and exactly evaluate the signal-to-noise-ratio of a multi-carrier source with non-flat noise floor. We have experimentally attain the worst case CNR of 22.5dB and 19.1dB for generated 50 and 69 flat low noise carriers, which has shown significant improvement than the previous cited works based on recirculating frequency shifter.

Reduced object related negativity response indicates impaired auditory scene analysis in adults with autistic spectrum disorder

Auditory Scene Analysis provides a useful framework for understanding atypical auditory perception in autism. Specifically, a failure to segregate the incoming acoustic energy into distinct auditory objects might explain the aversive reaction autistic individuals have to certain auditory stimuli or environments. Previous research with non-autistic participants has demonstrated the presence of an Object Related Negativity (ORN) in the auditory event related potential that indexes pre-attentive processes associated with auditory scene analysis. Also evident is a later P400 component that is attention dependent and thought to be related to decision-making about auditory objects. We sought to determine whether there are differences between individuals with and without autism in the levels of processing indexed by these components. Electroencephalography (EEG) was used to measure brain responses from a group of 16 autistic adults, and 16 age- and verbal-IQ-matched typically-developing adults. Auditory responses were elicited using lateralized dichotic pitch stimuli in which inter-aural timing differences create the illusory perception of a pitch that is spatially separated from a carrier noise stimulus. As in previous studies, control participants produced an ORN in response to the pitch stimuli. However, this component was significantly reduced in the participants with autism. In contrast, processing differences were not observed between the groups at the attention-dependent level (P400). These findings suggest that autistic individuals have difficulty segregating auditory stimuli into distinct auditory objects, and that this difficulty arises at an early pre-attentive level of processing.

Time Interleaved RF Carrier Modulations and Demodulations

This paper proposes a time-interleaved RF carrier modulation and demodulation technique, suitable for high frequency mixer applications under a constraint of active device speed limitation. The presents are in essence mixer arrays where modulated outputs by a series of time-delayed carriers with a reduced frequency, compared with a carrier frequency in fundamental mixers, will be interleaved in the time domain to synthesize the final output. The mixer arrays inherit an FIR filtering function, and the time interleaving process is equivalent to the filtering process where the arrays select the fundamental tone or its harmonics of a carrier in a periodic manner. The carrier waveform and duty-cycle play important roles in the noise performance of the mixer arrays. A comprehensive noise analysis is presented in this paper for both cases of correlated-noise and uncorrelated-noise mixer arrays. To minimize output noise power, optimization of carrier duty-cycle and noise filtering technique have been proposed and analyzed extensively for various types of carrier pulse. Finally analytical mismatch models are provided and output SNR degradations under finite mismatches amongst mixer array elements have been discussed based on the mismatch models. All theoretical analyses are verified through behavioral mixer array simulations including Monte-Carlo statistical simulations.

INFORMATION TRANSMISSION METHODS WITH THROUGH THE USE OF STOCHASTIC SIGNALS

The paper provides an overview of information transmission methods through the use of the noise carrier proposed by researchers from the middle of the last century to the present day. It is shown that the main areas of application of autocorrelation systems with the noise carrier is the confidential communication system construction, where the protection of the transmitted information from intercepting and protection of the channel from the extraneous information injecting are of priority. Methods of information transfer, discussed in the paper, allow solving the problem of sustainable communication in difficult conditions of signal propagation with simple technical means, especially in multipath channels. The paper studies the most urgent theoretical and practical problems relating to communication systems with the noise carrier.

The effects of noise vocoding on speech quality perception

Speech perception depends on access to spectral and temporal acoustic cues. Temporal cues include slowly varying amplitude changes (i.e. temporal envelope, TE) and quickly varying amplitude changes associated with the center frequency of the auditory filter (i.e. temporal fine structure, TFS). This study quantifies the effects of TFS randomization through noise vocoding on the perception of speech quality by parametrically varying the amount of original TFS available above 1500Hz. The two research aims were: 1) to establish the role of TFS in quality perception, and 2) to determine if the role of TFS in quality perception differs between subjects with normal hearing and subjects with sensorineural hearing loss. Ratings were obtained from 20 subjects (10 with normal hearing and 10 with hearing loss) using an 11-point quality scale. Stimuli were processed in three different ways: 1) A 32-channel noise-excited vocoder with random envelope fluctuations in the noise carrier, 2) a 32-channel noise-excited vocoder with the noise-carrier envelope smoothed, and 3) removal of high-frequency bands. Stimuli were presented in quiet and in babble noise at 18dB and 12dB signal-to-noise ratios. TFS randomization had a measurable detrimental effect on quality ratings for speech in quiet and a smaller effect for speech in background babble. Subjects with normal hearing and subjects with sensorineural hearing loss provided similar quality ratings for noise-vocoded speech.

Temporal Resolution With a Prescriptive Fitting Formula

Authors of previous work using laboratory-based paradigms documented that wide dynamic range compression (WDRC) may improve gap detection compared to linear amplification. The purpose of this study was to measure temporal resolution using WDRC fit with compression ratios set for each listener’s hearing loss. Nineteen adults with mild-to-moderate hearing loss fitted with WDRC or linear amplification set to a prescriptive fitting method participated in this study. Subjects detected amplitude modulations and gaps. Two types of noise carrier were used: narrowband (1995–2005 Hz) and broadband (100–8000 Hz). Small differences between WDRC and linear amplification were observed in the measures of temporal resolution. Modulation detection thresholds worsened by a mean of 0.7 dB with WDRC compared to linear amplification. This reduction was observed for both carrier types. Gap detection thresholds did not differ between the 2 amplification conditions. WDRC set using a prescriptive fitting method with individualized compression ratios had a small but statistically significant effect on measures of modulation thresholds. Differences were not observed between the two amplification conditions for the measures of gap detection. These findings contrast with previous work using fixed compression ratios, suggesting that the effect of the fitting method on the compression ratio should be considered when attempting to generalize the effect of WDRC on temporal resolution to the clinical setting.

Effect of Boundary Conditions on Thermal Noise of Intrinsic Terminal Currents in Bipolar Transistors Pertinent to Quasi-Ballistic Transport

This paper examines the impact of quasi-ballistic transport (QBT) on bipolar transistor (BJT) intrinsic terminal current noise by analytically solving the general 3-D minority carrier noise transport equation using Hansen's nonhomogenous boundary conditions with extensions to include injection noise. Transistor noises are further expressed in Y-parameters, as was done in the widely used van Vliet model, with extra corrections accounting for QBT. For 10-nm base width of BJTs without base built-in field, while QBT is significant in affecting IC, Sic is shown to be less than but close to the classic 2qIC.

Revisiting the loudness of sounds with asymmetric attack and decay

Stecker and Hafter [J. Acoust. Soc. Am. 107, 3358–3368 (2000)] compared the loudness of sounds whose envelopes had a fast attack and a slow decay (designated F-S) and a slow attack and a fast decay (designated S-F). They found that, for sinusoidal and broadband noise carriers, S-F stimuli were louder than F-S stimuli of equal energy. They argued that this effect could not be explained by current models of loudness and that the loudness effect may be related to the parsing of auditory input into direct and reverberant sound. Subsequent work has shown that the differences in loudness between F-S and S-F stimuli can be partially accounted for by the loudness model of Glasberg and Moore [J. Audio Eng. Soc. 50, 331–342 (2002)], which incorporates a form of temporal averaging that is asymmetric in time. However, the model does not account for the context effect found by Stecker and Hafter. The largest differences in loudness between F- S and S-F stimuli occurred after pre-exposure to a F-S stimulus. This may happen because, when successive sounds have similarly slow decays, the decaying part is attributed to room reverberation and contributes less to loudness.

Form and motion processing of second-order stimuli in color vision

We investigate whether there are second-order form and motion mechanisms in human color vision. Second-order stimuli are contrast modulations of a noise carrier. The contrast envelopes are static Gabors of different spatial frequencies (0.125-1 cycles/°) or drifting Gabors of different temporal frequencies (0.25 cycles/°, 0.5-4 Hz). Stimuli are isoluminant red-green or achromatic. Second-order form processing is measured using a simultaneous 2IFC (two-interval forced-choice) detection and orientation identification task, and direction identification is used for second-order motion processing. We find that for simple detection thresholds, chromatic performance is as good or better than achromatic performance, whereas for both motion and form tasks, chromatic performance is poorer than achromatic. Chromatic second-order form perception is very poor across all spatial and temporal frequencies measured and has a lowpass contrast modulation sensitivity function with a spatial cutoff of 1 cycle/° and temporal cutoff of 4 Hz. Chromatic second-order motion sensitivity is even poorer than for form and typically is limited to 1-2 Hz. To determine whether this residual motion processing might be based on feature tracking, we used the pedestal paradigm of Lu and Sperling (1995). We find that adding a static pedestal of the same spatial frequency as the drifting Gabor envelope, with its contrast set to 1-2 times its detection threshold, impairs motion direction performance for the chromatic stimuli but not the achromatic. This suggests that the motion of second-order chromatic stimuli is not processed by a second-order system but by a third-order, feature-tracking system, although a genuine second-order motion system exists for achromatic stimuli.

Spectral Context Affects Temporal Processing in Awake Auditory Cortex

Amplitude modulation encoding is critical for human speech perception and complex sound processing in general. The modulation transfer function (MTF) is a staple of auditory psychophysics, and has been shown to predict speech intelligibility performance in a range of adverse listening conditions and hearing impairments, including cochlear implant-supported hearing. Although both tonal and broadband carriers have been used in psychophysical studies of modulation detection and discrimination, relatively little is known about differences in the cortical representation of such signals. We obtained MTFs in response to sinusoidal amplitude modulation (SAM) for both narrowband tonal carriers and two-octave bandwidth noise carriers in the auditory core of awake squirrel monkeys. MTFs spanning modulation frequencies from 4 to 512 Hz were obtained using 16 channel linear recording arrays sampling across all cortical laminae. Carrier frequency for tonal SAM and center frequency for noise SAM was set at the estimated BF for each penetration. Changes in carrier type affected both rate and temporal MTFs in many neurons. Using spike discrimination techniques, we found that discrimination of modulation frequency was significantly better for tonal SAM than for noise SAM, though the differences were modest at the population level. Moreover, spike trains elicited by tonal and noise SAM could be readily discriminated in most cases. Collectively, our results reveal remarkable sensitivity to the spectral content of modulated signals, and indicate substantial interdependence between temporal and spectral processing in neurons of the core auditory cortex.

Amplitude modulation detection by human listeners in reverberant sound fields: Effects of prior listening exposure

Previous work [Zahorik et al., POMA, 15, 050002 (2012)] has reported that for both broadband and narrowband noise carrier signals in a simulated reverberant sound field, human sensitivity to amplitude modulation (AM) is higher than would be predicted based on the acoustical modulation transfer function (MTF) of the listening environment. These results may be suggestive of mechanisms that functionally enhance modulation in reverberant listening, although many details of this enhancement effect are unknown. Given recent findings that demonstrate improvements in speech understanding with prior exposure to reverberant listening environments, it is of interest to determine whether listening exposure to a reverberant room might also influence AM detection in the room, and perhaps contribute to the AM enhancement effect. Here, AM detection thresholds were estimated (using an adaptive 2-alternative forced-choice procedure) in each of two listening conditions: one in which consistent listening exposure to a particular room was provided, and a second that intentionally disrupted listening exposure by varying the room from trial-to-trial. Results suggest that consistent prior listening exposure contributes to enhanced AM sensitivity in rooms, but that it is not the sole determinant of the enhancement. [Work supported by the NIH/NIDCD.]

Spectrotemporal Modulation Sensitivity as a Predictor of Speech Intelligibility for Hearing-Impaired Listeners

A model that can accurately predict speech intelligibility for a given hearing-impaired (HI) listener would be an important tool for hearing-aid fitting or hearing-aid algorithm development. Existing speech-intelligibility models do not incorporate variability in suprathreshold deficits that are not well predicted by classical audiometric measures. One possible approach to the incorporation of such deficits is to base intelligibility predictions on sensitivity to simultaneously spectrally and temporally modulated signals. The likelihood of success of this approach was evaluated by comparing estimates of spectrotemporal modulation (STM) sensitivity to speech intelligibility and to psychoacoustic estimates of frequency selectivity and temporal fine-structure (TFS) sensitivity across a group of HI listeners. The minimum modulation depth required to detect STM applied to an 86 dB SPL four-octave noise carrier was measured for combinations of temporal modulation rate (4, 12, or 32 Hz) and spectral modulation density (0.5, 1, 2, or 4 cycles/octave). STM sensitivity estimates for individual HI listeners were compared to estimates of frequency selectivity (measured using the notched-noise method at 500, 1000, 2000, and 4000 Hz), TFS processing ability (2 Hz frequency-modulation detection thresholds for 500, 1000, 2000, and 4000 Hz carriers) and sentence intelligibility in noise (at a 0 dB signal-to-noise ratio) that were measured for the same listeners in a separate study. Eight normal-hearing (NH) listeners and 12 listeners with a diagnosis of bilateral sensorineural hearing loss participated. STM sensitivity was compared between NH and HI listener groups using a repeated-measures analysis of variance. A stepwise regression analysis compared STM sensitivity for individual HI listeners to audiometric thresholds, age, and measures of frequency selectivity and TFS processing ability. A second stepwise regression analysis compared speech intelligibility to STM sensitivity and the audiogram-based Speech Intelligibility Index. STM detection thresholds were elevated for the HI listeners, but only for low rates and high densities. STM sensitivity for individual HI listeners was well predicted by a combination of estimates of frequency selectivity at 4000 Hz and TFS sensitivity at 500 Hz but was unrelated to audiometric thresholds. STM sensitivity accounted for an additional 40% of the variance in speech intelligibility beyond the 40% accounted for by the audibility-based Speech Intelligibility Index. Impaired STM sensitivity likely results from a combination of a reduced ability to resolve spectral peaks and a reduced ability to use TFS information to follow spectral-peak movements. Combining STM sensitivity estimates with audiometric threshold measures for individual HI listeners provided a more accurate prediction of speech intelligibility than audiometric measures alone. These results suggest a significant likelihood of success for an STM-based model of speech intelligibility for HI listeners.

Brief Report: Atypical Neuromagnetic Responses to Illusory Auditory Pitch in Children with Autism Spectrum Disorders

Atypical auditory perception is a widely recognised but poorly understood feature of autism. In the current study, we used magnetoencephalography to measure the brain responses of 10 autistic children as they listened passively to dichotic pitch stimuli, in which an illusory tone is generated by sub-millisecond inter-aural timing differences in white noise. Relative to control stimuli that contain no inter-aural timing differences, dichotic pitch stimuli typically elicit an object related negativity (ORN) response, associated with the perceptual segregation of the tone and the carrier noise into distinct auditory objects. Autistic children failed to demonstrate an ORN, suggesting a failure of segregation; however, comparison with the ORNs of age-matched typically developing controls narrowly failed to attain significance. More striking, the autistic children demonstrated a significant differential response to the pitch stimulus, peaking at around 50ms. This was not present in the control group, nor has it been found in other groups tested using similar stimuli. This response may be a neural signature of atypical processing of pitch in at least some autistic individuals.