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Predictive-coding has justifiably become a highly influential theory in Neuroscience. However, the possibility of its unfalsifiability has been raised. We argue that if predictive-coding were unfalsifiable, it would be a problem, but there are patterns of behavioural and neuroimaging data that would stand against predictive-coding. Contra (vanilla) predictive patterns are those in which the more expected stimulus generates the largest evoked-response. However, basic formulations of predictive-coding mandate that an expected stimulus should generate little, if any, prediction error and thus little, if any, evoked-response. It has, though, been argued that contra (vanilla) predictive patterns can be obtained if precision is higher for expected stimuli. Certainly, using precision, one can increase the amplitude of an evoked-response, turning a predictive into a contra (vanilla) predictive pattern. We demonstrate that, while this is true, it does not present an absolute barrier to falsification. This is because increasing precision also reduces latency and increases the frequency of the response. These properties can be used to determine whether precision-weighting in predictive-coding justifiably explains a contra (vanilla) predictive pattern, ensuring that predictive-coding is falsifiable. • Assess falsifiability of predictive coding. • Review predictive coding and present a canonical model of it. • Identify data patterns that stand against predictive coding. • Outline competing theories to predictive coding. [ABSTRACT FROM AUTHOR]

In this study, a composite robust control approach with non‐singular terminal sliding mode control and fixed‐time disturbance observer (FxTDO) is proposed for a class of second‐order non‐linear systems in the presence of matched uncertain disturbances. A bi‐limit‐weighted homogeneous FxTDO is designed based on the efficient utilisation of power functions obtained by the differentiation error amplification strategy. The FxTDO enjoys a fast convergence rate and simple parameters tuning process. By introducing the disturbance estimation to directly compensate the total disturbance in the composite control law, only a particular small gain‐based discontinuous control term is needed to guarantee the existence of sliding mode, and chattering phenomenon can be attenuated. The simulation results revealed the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In some orthogonal frequency division multiplexing (OFDM) systems, a number of OFDM symbols form one subframe and consecutive subframes may be allocated to different users. The power estimation and the gain adjustment need to be carried out within the cyclic prefix (CP) of the first OFDM symbol in a subframe. After passing through the multipath channel, the CP of the first OFDM symbol in a subframe contains a portion of the power of the last OFDM symbol in the prior subframe. When these two subframes are allocated to distinct users with different received powers, the gain adjustment is inaccurate and the system performance is degraded. To combat the inter-user interference at the boundary of subframes, the CP of the first OFDM symbol in a subframe is proposed to include an adjustment portion (AP). The overhead of the AP is amortized over the OFDM symbols in a subframe and is negligible when the number of OFDM symbols in a subframe is large. A model is given to calculate the optimal length of the AP in this paper. The model uses an information theory to formulate the tradeoff between the accuracy of power measurement and the overhead of the AP. [ABSTRACT FROM AUTHOR]

Teleoperated robot systems are able to support humans to accomplish their tasks in many applications. However, the performance of teleoperation largely depends on motor functionality and human operator’s skill, especially when a human operator is short of skill training. In order to adapt to various unstructured environments for the robot system and the human operator, in this paper, a teleoperation scheme using integrated tremor attenuation with a variable gain control algorithm involving surface electromyogram is proposed to achieve personalized control performance and to reduce reliance on operator’s skill. For attenuating tremor, a filter based on support vector machine is developed to guarantee normal operation. This filter depends on the machine learning scheme and does not rely on a priori filter parameters. Semiphysical experiments have been performed to demonstrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

The neocortex is thought to employ a number of canonical computations, but little is known about whether these computations rely on shared mechanisms across different neural populations. In recent years, the mouse has emerged as a powerful model organism for the dissection of the circuits and mechanisms underlying various aspects of neural processing and therefore provides an important avenue for research into putative canonical computations. One such computation is contrast gain control, the systematic adjustment of neural gain in accordance with the contrast of sensory input, which helps to construct neural representations that are robust to the presence of background stimuli. Here, we characterized contrast gain control in the mouse auditory cortex. We performed laminar extracellular recordings in the auditory cortex of the anesthetized mouse while varying the contrast of the sensory input. We observed that an increase in stimulus contrast resulted in a compensatory reduction in the gain of neural responses, leading to representations in the mouse auditory cortex that are largely contrast invariant. Contrast gain control was present in all cortical layers but was found to be strongest in deep layers, indicating that intracortical mechanisms may contribute to these gain changes. These results lay a foundation for investigations into the mechanisms underlying contrast adaptation in the mouse auditory cortex. NEW & NOTEWORTHY We investigated whether contrast gain control, the systematic reduction in neural gain in response to an increase in sensory contrast, exists in the mouse auditory cortex. We performed extracellular recordings in the mouse auditory cortex while presenting sensory stimuli with varying contrasts and found this form of processing was widespread. This finding provides evidence that contrast gain control may represent a canonical cortical computation and lays a foundation for investigations into the underlying mechanisms. [ABSTRACT FROM AUTHOR]

When making decisions, humans are often distracted by irrelevant information. Distraction has a different impact on perceptual, cognitive, and value-guided choices, giving rise to well-described behavioral phenomena such as the tilt illusion, conflict adaptation, or economic decoy effects. However, a single, unified model that can account for all these phenomena has yet to emerge. Here, we offer one such account, based on adaptive gain control, and additionally show that it successfully predicts a range of counterintuitive new behavioral phenomena on variants of a classic cognitive paradigm, the Eriksen flanker task. We also report that blood oxygen level-dependent signals in a dorsal network prominently including the anterior cingulate cortex index a gainmodulated decision variable predicted by the model. This work unifies the study of distraction across perceptual, cognitive, and economic domains. [ABSTRACT FROM AUTHOR]

In practical applications, the signal-to-noise ratio (SNR), reliability, and the long-term stability of wavelength modulation spectroscopy (WMS) system is limited by the non-absorption transmission loss. In this investigation, we report on a signal recovery method to remove the impact of non-absorption transmission loss based on an automatic gain closed-loop control. The deviation of the WMS system with the introduced signal recovery method has been observed to be below 4.27% under the non-absorption transmission loss which varied from 0 dB to −6.02 dB, and is about 13 times lower than the ordinary system. The proposed method is suitable for promoting the reliability and stability of WMS system under rigorous circumstances. Besides, it has the potential value in the multi-point detection or to achieve a higher SNR. [ABSTRACT FROM AUTHOR]

This paper presents a subband-decomposed image-enhancement algorithm that can preserve the luminance and contrast levels in power-controllable thin-film-transistor liquid-crystal display devices. The proposed algorithm consists of three steps. First, an input image is decomposed to multiscale subbands via subband decomposition. Second, luminance compensation and contrast preservation are achieved simultaneously by adjusting the gain of each subband properly. Third, additional power consumption caused by excessive boosting, while coping with the local dimming through specific clipping, is prevented. The experimental results show that the proposed algorithm provides more natural details and contrast, while preserving more similarities with the original, than the existing methods. Even in terms of the peak signal-to-noise-ratio and the structural similarity index, the proposed algorithm has 27.8% and 3.8% higher values compared to a state-of-the-art method. The real-time operation of the proposed algorithm was verified through intensive optimization and the Compute Unified Device Architecture implementation. In addition, the power-reduction effect of the proposed algorithm on commercial monitors was investigated experimentally. [ABSTRACT FROM AUTHOR]

This brief presents a 5.8 GHz digitally controlled dedicated short range communications (DSRC) receiver for Chinese electronic toll collection systems. All RF, IF blocks and digital baseband for on-chip automatic gain control, are integrated on an RF system-on-chip (RF-SoC). The proposed digitally controlled low noise amplifier (LNA) and mixer circuits are elaborated. The test chip was realized in a 0.13- \mu \textm CMOS technology. The RF blocks in receiver occupy a chip area of 0.75 mm2. The receiver blocks consume 22 mA under a 1.5-V supply voltage. Measurement results show that the bit error rate maintains better than 10−6, while the input power level varies from −75 dBm to −8 dBm. This design results in a receiver sensitivity improvement of at least 25%, and a dynamic range enhancement of at least 12%. [ABSTRACT FROM PUBLISHER]

A neutral density filter placed before one eye will produce a dichoptic imbalance in luminance, which attenuates responses to visual stimuli and lags neural signals from retina to cortex in the filtered eye. When stimuli are presented to both the filtered and unfiltered eye (i.e., binocularly), neural responses show little attenuation and no lag compared with their baseline counterpart. This suggests that binocular visual mechanisms must suppress the attenuated and delayed input from the filtered eye; however, the mechanisms involved remain unclear. Here, we used a Steady-State Visual Evoked Potential (SSVEP) technique to measure neural responses to monocularly and binocularly presented stimuli while observers wore an ND filter in front of their dominant eye. These data were well-described by a binocular summation model, which received the sinusoidal contrast modulation of the stimulus as input. We incorporated the influence of the ND filter with an impulse response function, which adjusted the input magnitude and phase in a biophysically plausible manner. The model captured the increase in attenuation and lag of neural signals for stimuli presented to the filtered eye as a function of filter strength, while also generating the filter phase-invariant responses from binocular presentation for EEG and psychophysical data. These results clarify how binocular visual mechanisms—specifically interocular suppression—can suppress the delayed and attenuated signals from the filtered eye and maintain normal neural signals under imbalanced luminance conditions. [ABSTRACT FROM AUTHOR]

Erbium-doped fiber amplifiers are a promising solution for the signal amplification in long-haul mode-division multiplexed transmission systems. In order to minimize signal degradations by these amplifiers, low mode dependent gain and noise figures are desirable. We propose a scalable mode dependent gain equalization scheme for the 1480-nm pump wavelength. Contrary to the 980-nm pump wavelength, each signal mode has a maximum overlap with only one pump mode. Due to this, a scalable mode selective gain control is achievable by adjusting the pump modes. In this letter, we demonstrate the scalability of our approach with the number of signal modes by numerical simulation. Furthermore, we propose a two-stage amplifier setup in which the mode dependent gain of both stages is compensated in the second stage, pumped at a wavelength of 1480 nm. [ABSTRACT FROM AUTHOR]

Most of our knowledge about vision comes from experiments in which stimuli are presented to immobile human subjects or animals. In the case of human subjects, movement during psychophysical, electrophysiological, or neuroimaging experiments is considered to be a source of noise to be eliminated. Animals used in visual neuroscience experiments are typically restrained and, in many cases, anesthetized. In reality, however, vision is often used to guide the motion of awake, ambulating organisms. Recent work in mice has shown that locomotion elevates visual neuronal response amplitudes (Niell and Stryker, 2010; Erisken et al., 2014; Fu et al., 2014; kee et ak, 2014; Mineault et al., 2016) and reduces long-range gain control (Ayaz et al., 2013). Here, we used both psychophysics and steady-state electrophysiology to investigate whether similar effects of locomotion on early visual processing can be measured in humans. Our psychophysical results show that brisk walking has little effect on subjects' ability to detect briefly presented contrast changes and that co-oriented flankers are, if anything, more effective masks when subjects are walking. Our electrophysiological data were consistent with the psychophysics indicating no increase in stimulus-driven neuronal responses while walking and no reduction in surround suppression. In summary, we have found evidence that early contrast processing is altered by locomotion in humans but in a manner that differs from that reported in mice. The effects of locomotion on very low-level visual processing may differ on a species-by-species basis and may reflect important differences in the levels of arousal associated with locomotion. [ABSTRACT FROM AUTHOR]

The excitotoxic theory of Parkinson's disease (PD) hypothesizes that a pathophysiological degeneration of dopaminergic neurons stems from neural hyperactivity at early stages of disease, leading to mitochondrial stress and cell death. Recent research has harnessed the visual system of Drosophila PD models to probe this hypothesis. Here, we investigate whether abnormal visual sensitivity and excitotoxicity occur in early-onset PD (EOPD) Drosophila models DJ-1αΔ72, DJ-1βΔ 93, and PINK15. We used an electroretinogram to record steady-state visually evoked potentials driven by temporal contrast stimuli. At 1 day of age, all EOPD mutants had a twofold increase in response amplitudes compared with w̄ controls. Furthermore, we found that excitotoxicity occurs in older EOPD models after increased neural activity is triggered by visual stimulation. In an additional analysis, we used a linear discriminant analysis to test whether there were subtle variations in neural gain control that could be used to classify Drosophila into their correct age and genotype. The discriminant analysis was highly accurate, classifying Drosophila into their correct genotypic class at all age groups at 50-70% accuracy (20% chance baseline). Differences in cellular processes link to subtle alterations in neural network operation in young flies, all of which lead to the same pathogenic outcome. Our data are the first to quantify abnormal gain control and excitotoxicity in EOPD Drosophila mutants. We conclude that EOPD mutations may be linked to more sensitive neuronal signaling in prodromal animals that may cause the expression of PD symptomologies later in life. NEW & NOTEWORTHY Steady-state visually evoked potential response amplitudes to multivariate temporal contrast stimuli were recorded in early-onset PD Drosophila models. Our data indicate that abnormal gain control and a subsequent visual loss occur in these PD mutants, supporting a broader excitotoxicity hypothesis in genetic PD. Furthermore, linear discriminant analysis could accurately classify Drosophila into their correct genotype at different ages throughout their lifespan. Our results suggest increased neural signaling in prodromal PD patients. [ABSTRACT FROM AUTHOR]

This paper proposes a feedback time difference amplifier (FTDA) that achieves linear, controllable gain and changeable input range for different time difference gains. The proposed FTDA consists of two identical feedback output generators. The feedback output generator achieves a linear input–output transfer characteristic by employing two p-type keepers for time gain feedback control. Its validity was demonstrated using 0.13μm SiGe BiCMOS process. The power consumption is 91.54μW for the highest gain with input signals at 2MHz. The gain can be controlled from 25.06 to 734.9s/s within 40ps input time interval. [ABSTRACT FROM AUTHOR]

In the mammalian retina, horizontal cells receive glutamatergic inputs from many rod and cone photoreceptors and return feedback signals to them, thereby changing photoreceptor glutamate release in a light-dependent manner. Horizontal cells also provide feedforward signals to bipolar cells. It is unclear, however,howhorizontal cell signals also affect the temporal, spatial,andcontrast tuning in retinal output neurons, the ganglion cells.Tostudy this,wegenerated a genetically modifiedmouseline inwhichweeliminated the lightdependencyof feedbackbydeleting glutamate receptors from mouse horizontal cells. This genetic modification allowed us to investigate the impact of horizontal cells on ganglion cell signaling independent of the actualmodeof feedback in the outer retina and without pharmacological manipulation of signal transmission. In control and genetically modified mice (both sexes), we recorded the light responses of transient OFF-+ retinal ganglion cells in the intact retina. Excitatory postsynaptic currents (EPSCs) were reduced and the cells were tuned to lower temporal frequencies and higher contrasts, presumably because photoreceptor output was attenuated. Moreover, receptive fields of recorded cells showed a significantly altered surround structure. Our data thus suggest that horizontal cells are responsible for adjusting the dynamic range of retinal ganglion cells and, together with amacrine cells, contribute to the center/surround organization of ganglion cell receptive fields in the mouse. [ABSTRACT FROM AUTHOR]

This paper presents the design and measurements of a 32-Gb/s differential-input differential-output transimpedance amplifier (TIA) employed in dual polarization integrated coherent receivers for 100-Gb Ethernet. A circuit technique is shown that uses a replica TIA to stabilize the operating point of the two shunt-feedback input stages as well as to cancel the dc part of the two complementary input currents and balances their offset. The TIA can be operated in two modes, an automatic gain control mode to retain a good total harmonic distortion (THD) over a wide dynamic range and a manual gain control mode. Electrical as well as optical-electrical characterization of the TIA are presented. It achieves a maximum differential transimpedance of 74 dB \Omega , 33 GHz of 3-dB bandwidth, 12.2 pA/ \sqrt {\text {Hz}} of average input-referred noise current density with the photodiode, 900 mVpp of maximum differential output swing, less than 1% of THD for 600 mVpp differential output swing, and 500 \mu \text{A}_{\text {pp}}$ differential input current. The linearity of the TIA is furthermore demonstrated with PAM4 measurements at 25 Gbaud. The dual TIA chip is fabricated in a 0.13- \mu \text{m} SiGe:C BiCMOS technology, dissipates 436 mW of power and occupies 2 mm2 of area. [ABSTRACT FROM PUBLISHER]

This study is concerned with the adaptive stabilisation problem for a class of large‐scale output‐constrained non‐linear time‐delay systems in strict‐feedback form. The investigative system satisfies a more general growth condition and the precise knowledge of the time delay is not required to be known a priori. Firstly, an observer is designed by the dynamic gain control design technique. Then, based on a novel Lyapunov–Krasovskii functional, the output constraints are satisfied and the stability of the closed‐loop control system is achieved. Finally, a numerical example is given to demonstrate the effectiveness of the proposed design procedure. [ABSTRACT FROM AUTHOR]

A programmable-gain amplifier with low power consumption is presented. The programmable gain function is achieved by varying the effective transconductance ratios of input and output stages, which is realized through innovative binary-weighted and triode-region transistor ladder. The proposed technique effectively overcomes the problems associated with the implementation of resistors ladder in these types of structures. The operational principle of this unique structure is discussed, its most important formulas are derived, and its outstanding performance is verified by post-layout simulations in TSMC 0.18- $\mu$ m N-well CMOS fabrication process. Owing to its unique construction, the proposed circuit combines the ever interesting constant bandwidth, linear-in-decibel, and fine-step programmable gain range merits all in a simple and low power structure. The core of proposed structure draws only 36.5 $\mu$ W from 1.8-V power supply. The circuit is capable of delivering a wide programmable range of about 37 dB and operating at frequencies up to 20 MHz. To approve the robustness of the structure, full process, voltage, and temperature variation analysis of the circuit is investigated through corner case and Monte Carlo simulations. Monte Carlo simulations show standard deviation values of less than 0.21 $\mu$ W and 0.5 dB in power consumption and voltage gain, respectively. These results indicate that the proposed structure would lend itself well for use in applications that demand high ratios of frequency over power consumption. [ABSTRACT FROM AUTHOR]

An improved topology for the baseband super-regenerative sampling amplifier is proposed and analyzed, which employs a series-capacitors output load to realize positive feedback. As in the conventional circuit, the gain of the amplifier is continuously variable by controlling the length of the capacitor charging phase. It is shown that decreasing feedback enhances the linearity of the circuit while trading off with a lower sampling speed. Entirely removing the feedback yields the integrating amplifier circuit. This is a practical implementation in terms of linearity, power, noise, and gain in low-frequency applications, including biomedical signal amplification. The analysis is verified by measured results from an integrated circuit prototype in 180-nm CMOS technology. [ABSTRACT FROM AUTHOR]

Animals navigating in natural environments must handle vast changes in their sensory input. Visual systems, for example, handle changes in luminance at many timescales, from slow changes across the day to rapid changes during active behavior. To maintain luminance-invariant perception, visual systems must adapt their sensitivity to changing luminance at different timescales. We demonstrate that luminance gain control in photoreceptors alone is insufficient to explain luminance invariance at both fast and slow timescales and reveal the algorithms that adjust gain past photoreceptors in the fly eye. We combined imaging and behavioral experiments with computational modeling to show that downstream of photoreceptors, circuitry taking input from the single luminance-sensitive neuron type L3 implements gain control at fast and slow timescales. This computation is bidirectional in that it prevents the underestimation of contrasts in low luminance and overestimation in high luminance. An algorithmic model disentangles these multifaceted contributions and shows that the bidirectional gain control occurs at both timescales. The model implements a nonlinear interaction of luminance and contrast to achieve gain correction at fast timescales and a dark-sensitive channel to improve the detection of dim stimuli at slow timescales. Together, our work demonstrates how a single neuronal channel performs diverse computations to implement gain control at multiple timescales that are together important for navigation in natural environments. [Display omitted] • Luminance-invariant behavior uses fast and slow gain control beyond photoreceptors • Absolute luminance-sensitive L3 neurons mediate both gain increments and decrements • A computational model disentangles the L3-mediated gain correction by timescales • Gain control by the L3 pathway is bidirectional at both fast and slow timescales Combining fly behavior, in vivo imaging, and computational modeling, Ketkar and Shao et al. uncover distinct luminance gain control operations occurring downstream of the luminance-sensitive L3 neurons. This multifaceted gain control achieves luminance-invariant behavior at both fast and slow timescales and improves dim light vision. [ABSTRACT FROM AUTHOR]

Homeostatic plasticity is a stabilizing mechanism commonly observed in real neural systems that allows neurons to maintain their activity around a functional operating point. This phenomenon can be used in neuromorphic systems to compensate for slowly changing conditions or chronic shifts in the system configuration. However, to avoid interference with other adaptation or learning processes active in the neuromorphic system, it is important that the homeostatic plasticity mechanism operates on time scales that are much longer than conventional synaptic plasticity ones. In this paper we present an ultralow leakage circuit, integrated into an automatic gain control scheme, that can implement the synaptic scaling homeostatic process over extremely long time scales. Synaptic scaling consists in globally scaling the synaptic weights of all synapses impinging onto a neuron maintaining their relative differences, to preserve the effects of learning. The scheme we propose controls the global gain of analog log-domain synapse circuits to keep the neuron's average firing rate constant around a set operating point, over extremely long time scales. To validate the proposed scheme, we implemented the ultralow leakage synaptic scaling homeostatic plasticity circuit in a standard 0.18 $\mu$m complementary metal-oxide-semiconductor process, and integrated it in an array of dynamic synapses connected to an adaptive integrate and fire neuron. The circuit occupies a silicon area of 84  $\mu$m $\times$ 22 $\mu$m and consumes approximately 10.8 nW with a 1.8 V supply voltage. We present experimental results from the homeostatic circuit and demonstrate how it can be configured to exhibit time scales of up to 100 ks, thanks to a controllable leakage current that can be scaled down to 0.45 aA (2.8 electrons per second). [ABSTRACT FROM PUBLISHER]

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A differential variable gain amplifier (VGA) for wideband baseband signals has been designed, analyzed, and implemented in a 0.25- \rm \mu m InP double heterojunction bipolar transistor technology with f_{T}/f_{\mathrm{ max}} of 370/650 GHz. The 3-dB frequency bandwidth is measured to be 40 GHz with a maximum gain of 31 dB, resulting in a gain bandwidth product (GBP) of 1.4 THz, four times higher than previously reported GBP from a Gilbert cell-based VGAs. Furthermore, it measures a gain control range of 44 dB, a noise figure of 6.2 dB, an output third-order intercept point of 17 dBm, and a total power consumption of 350 mW from a single −7-V supply. With pseudorandom binary sequence test pattern signals, a clear open eye at 44 Gb/s was observed. The complete circuit, including on-chip integrated bias network and pads, measures 0.77 \rm mm^{2}$ . We analyze the VGA for the 3-dB bandwidth and GBP by the use of zero-value time constants method to analytically identify the maximum GBP with respect to the design parameters and current bias. [ABSTRACT FROM AUTHOR]

A dual-mode radio frequency CMOS power amplifier (PA) for Internet of Things application is presented, which is integrated with the other circuits in a 55-nm bulk CMOS process. The low-power mode is achieved by reducing the number of turn-on power transistors, which are also used for linearization. The PA has a gain control scheme that functions by controlling the transconductance ( gm ) of the driver stage. A simple body network is introduced to common gate power transistors to improve the linearity of the PA. It is measured with 802.11n 64-quadrature-amplitude-modulation (MCS7) signal and shows a maximum average power of 16 dBm with a supply current of 222 mA under an error-vector-magnitude of −27 dB, which is packaged in a QFN 5 \times \,\, 5 mm. [ABSTRACT FROM PUBLISHER]

Light intensities (photons s-1 μm-2) in a natural scene vary over several orders of magnitude from shady woods to direct sunlight. A major challenge facing the visual system is how to map such a large dynamic input range into its limited output range, so that a signal is neither buried in noise in darkness nor saturated in brightness. A fly photoreceptor has achieved such a large dynamic range; it can encode intensity changes from single to billions of photons, outperforming man-made light sensors. This performance requires powerful light adaptation, the neural implementation of which has only become clear recently. A computational fly photoreceptor model, which mimics the real phototransduction processes, has elucidated how light adaptation happens dynamically through stochastic adaptive quantal information sampling. A Drosophila R1-R6 photoreceptor's light sensor, the rhabdomere, has 30,000 microvilli, each of which stochastically samples incoming photons. Each microvillus employs a full G-protein-coupled receptor signalling pathway to adaptively transduce photons into quantum bumps (QBs, or samples). QBs then sum the macroscopic photoreceptor responses, governed by four quantal sampling factors (limitations): (i) the number of photon sampling units in the cell structure (microvilli), (ii) sample size (QB waveform), (iii) latency distribution (time delay between photon arrival and emergence of a QB), and (iv) refractory period distribution (time for a microvillus to recover after a QB). Here, we review how these factors jointly orchestrate light adaptation over a large dynamic range. [ABSTRACT FROM AUTHOR]

Bayesian inference provides a cogent account of how the brain combines sensory information with “priors” based on past experience to guide many behaviors, including smooth pursuit eye movements. We now demonstrate very rapid adaptation of the pursuit system’s priors for target direction and speed. We go on to leverage that adaptation to outline possible neural mechanisms that could cause pursuit to show features consistent with Bayesian inference. Adaptation of the prior causes changes in the eye speed and direction at the initiation of pursuit. The adaptation appears after a single trial and accumulates over repeated exposure to a given history of target speeds and directions. The influence of the priors depends on the reliability of visual motion signals: priors are more effective against the visual motion signals provided by low-contrast vs. high-contrast targets. Adaptation of the direction prior generalizes to eye speed and vice versa, suggesting that both priors could be controlled by a single neural mechanism. We conclude that the pursuit system can learn the statistics of visual motion rapidly and use those statistics to guide future behavior. Furthermore, a model that adjusts the gain of visual-motor transmission predicts the effects of recent experience on pursuit direction and speed, as well as the specifics of the generalization between the priors for speed and direction. We suggest that Bayesian inference in pursuit behavior is implemented by distinctly non-Bayesian internal mechanisms that use the smooth eye movement region of the frontal eye fields to control of the gain of visual-motor transmission. NEW & NOTEWORTHY Bayesian inference can account for the interaction between sensory data and past experience in many behaviors. Here, we show, using smooth pursuit eye movements, that the priors based on past experience can be adapted over a very short time frame. We also show that a single model based on direction-specific adaptation of the strength of visual-motor transmission can explain the implementation and adaptation of priors for both target direction and target speed. [ABSTRACT FROM AUTHOR]

Toothed whales have evolved to live in extremely different habitats and yet they all rely strongly on echolocation for finding and catching prey. Such biosonar-based foraging involves distinct phases of searching for, approaching and capturing prey, where echolocating animals gradually adjust sonar output to actively shape the flow of sensory information. Measuring those outputs in absolute levels requires hydrophone arrays centred on the biosonar beam axis, but this has never been done for wild toothed whales approaching and capturing prey. Rather, field studies make the assumption that toothed whales will adjust their biosonar in the same manner to arrays as they will when approaching prey. To test this assumption, we recorded wild botos (Inia geoffrensis) as they approached and captured dead fish tethered to a hydrophone in front of a star-shaped seven-hydrophone array. We demonstrate that botos gradually decrease interclick intervals and output levels during prey approaches, using stronger adjustment magnitudes than predicted from previous boto array data. Prey interceptions are characterised by high click rates, but although botos buzz during prey capture, they do so at lower click rates than marine toothed whales, resulting in a much more gradual transition from approach phase to buzzing. We also demonstrate for the first time that wild toothed whales broaden biosonar beamwidth when closing in on prey, as is also seen in captive toothed whales and bats, thus resulting in a larger ensonified volume around the prey, probably aiding prey tracking by decreasing the risk of prey evading ensonification. [ABSTRACT FROM AUTHOR]

This paper presents a flexible-reach 0.5–16.3 Gb/s serial transceiver which is integrated into a field-programmable gate array (FPGA) and fabricated in 16-nm FinFET CMOS. The transceiver is fully adaptive to cover the FPGA requirement to support a multitude of combinations of data-rates and standards such as 10 G-KR, PCIe Gen3/4, and SFP+ across a wide range of channel loss profiles. High-performance techniques employed include a fully adaptive continuous-time linear equalizer, automatic gain control, an 11-tap decision feedback equalizer, wideband LC phase-locked loops, and a high-tracking-bandwidth clock and data recovery loop with low latency. Low-power techniques such as half-rate clocking, active inductors and data-rate programmability are employed to meet stringent power budgets at the different rates. At 16.3 Gb/s, the receiver has a jitter tolerance of >0.3UI at 100 MHz. The transceiver achieves a bit error rate < 10e − 15 with up to 28-dB loss at Nyquist. It consumes 219 mW/channel at 16.3 Gb/s. The design has robust performance across process, voltage, and temperature, and the architecture allows for a high degree of tuning to handle different system environments in deployment. [ABSTRACT FROM AUTHOR]

An assessment of non-geophysical effects in spaceborne global navigation satellite system reflectometry (GNSS-R) data from the UK TechDemoSat-1 (TDS-1) mission is presented. TDS-1 was launched in July 2014 and provides the first new spaceborne GNSS-R data since the pioneering UK-disaster monitoring constellation experiment in 2003. Non-geophysical factors evaluated include ambient L-band noise, instrument operating mode, and platform-related parameters. The findings are particularly relevant to users of uncalibrated GNSS-R signals for the retrieval of geophysical properties of the Earth surface. Substantial attitude adjustments of the TDS-1 platform are occasionally found to occur that introduce large uncertainties in parts of the TDS-1 GNSS-R dataset, particularly for specular points located outside the main beam of the nadir antenna where even small attitude errors can lead to large inaccuracies in the geophysical inversion. Out of eclipse however, attitude adjustments typically remain smaller than 1.5°, with larger deviations of up to 10° affecting less than 5% of the overall sun-lit data. Global maps of L1 ambient noise are presented for both automatic and programmed gain modes of the receiver, revealing persistent L-band noise hotspots along the Equator that can reach up to 2.5 dB, most likely associated with surface reflection of signals from other GNSS transmitters and constellations. Sporadic high-power noise events observed in certain regions point to sources of human origin. Relevant conclusions of this study are that platform attitude knowledge is essential and that radiometric calibration of GNSS-R signals should be used whenever possible. Care should be taken when considering using noise measurements over the equatorial oceans for calibration purposes, as ambient noise and correlated noise in delay–Doppler maps both show more variation than might be expected over these regions. [ABSTRACT FROM PUBLISHER]

Multipath effects in airborne analogue voice amplitude modulation communications have been characterized using air-to-air communications radiofrequency recordings for the first time. The different paths followed by the direct wave and reflected waves give rise to a Doppler shift difference, which produces a characteristic noise or voice modulation depending on the fading depth, Doppler shift, and the speed of the automatic gain control of the receiver. Scattered reflected waves would also increase the perceived noise at reception. [ABSTRACT FROM PUBLISHER]

Summary In senses as diverse as vision, hearing, touch, and the electrosense, sensory neurons receive bottom-up input from the environment, as well as top-down input from feedback loops involving higher brain regions [ 1–4 ]. Through connectivity with local inhibitory interneurons, these feedback loops can exert both positive and negative control over fundamental aspects of neural coding, including bursting [ 5, 6 ] and synchronous population activity [ 7, 8 ]. Here we show that a prominent midbrain feedback loop synthesizes a neural code for motion reversal in the hindbrain electrosensory ON- and OFF-type pyramidal cells. This top-down mechanism generates an accurate bidirectional encoding of object position, despite the inability of the electrosensory afferents to generate a consistent bottom-up representation [ 9, 10 ]. The net positive activity of this midbrain feedback is additionally regulated through a hindbrain feedback loop, which reduces stimulus-induced bursting and also dampens the ON and OFF cell responses to interfering sensory input [ 11 ]. We demonstrate that synthesis of motion representations and cancellation of distracting signals are mediated simultaneously by feedback, satisfying an accepted definition of spatial attention [ 12 ]. The balance of excitatory and inhibitory feedback establishes a “focal” distance for optimized neural coding, whose connection to a classic motion-tracking behavior provides new insight into the computational roles of feedback and active dendrites in spatial localization [ 13, 14 ]. [ABSTRACT FROM AUTHOR]

In this paper, we present a method to implement concurrent dual-band digital predistortion (DPD) models using 2-D lookup tables (LUTs) with bilinear interpolation and extrapolation. We introduce the required set of basis functions to describe this model. The DPD output is expressed as a linear combination of these basis functions and we show how to directly estimate the coefficients using least squares. We introduce a flexible 2-D bilinear extrapolation scheme that is ideally suited to dual-band signals with high peak-to-average power ratio. We show how these are needed when digital predistortion is implemented in conjunction with automatic gain control. We also introduce example dual-band polynomial models with memory and show how to create a similar memory model based on 2-D lookup tables with bilinear interpolation. One such model is the dual-band generalized memory polynomial model. Laboratory experiments are performed using such a 2-D LUT with bilinear interpolation model. [ABSTRACT FROM PUBLISHER]

Silicon Photo-Multipliers (SiPM) are regarded as novel photo-detectors to replace conventional Photo-Multiplier Tubes (PMTs). However, the breakdown voltage dependence on the ambient temperature results in a gain variation of ∼3%/°C. This severely limits the application of this device in experiments with wide range of operating temperature, especially in space missions. An experimental setup was established to investigate the temperature and bias voltage dependence of gain for the Multi-Pixel Photon Counter (MPPC). The gain and breakdown voltage dependence on operating temperature of an MPPC can be approximated by a linear function, which is similar to the behavior of a zener diode. The measured temperature coefficient of the breakdown voltage is (59.4±0.4 mV)/°C. According to this fact, an analog power supply based on two zener diodes and an operational amplifier was designed with a positive temperature coefficient. The measured temperature dependence for the designed power supply is between 63.65–64.61 mV/°C at different output voltages. The designed power supply can bias the MPPC at an over-voltage with a temperature variation of ∼5 mV/°C. The gain variation of the MPPC biased at over-voltage of 2 V was reduced from 2.8 % / ° C to 0.3 % / ° C when biased the MPPC with the designed power supply for gain control. Detailed design and performance of the analog power supply in the temperature range from − 42.7 ° C to 20.9 ° C will be discussed in this paper. [ABSTRACT FROM AUTHOR]

Contrast sensitivity is regulated by neural mechanisms that flexibly adjust responsiveness to optimize stimulus encoding across different environments. Here we studied the developmental status of gain control mechanisms in school-age children (5-17years) and adults using a visual masking paradigm. A variable contrast, spatially random 2-D noise test pattern was masked by the presence of a superimposed independent noise pattern presented at 0, 12 and 40% contrast. Frequency-tagged steady state visual evoked potentials were used to separately record responses to the test (5.14Hz) and the mask (7.2Hz). By incrementally increasing the test contrast we measured contrast response functions for each mask contrast. The unmasked contrast response functions were largely similar in shape across age, but peak amplitude was higher in the children. Masking shifted the contrast response function rightward on the contrast axis in both the adults and older children, elevating contrast thresholds by a similar factor across age. However, in younger children, masking resulted in a change in the slope of the contrast response function. These findings suggest that immaturity in the contrast normalization process persists until approximately 11years of age. [ABSTRACT FROM AUTHOR]

In this paper, we present a method to implement digital predistortion (DPD) memory models using lookup tables (LUTs) with linear interpolation and extrapolation. We introduce the required set of basis functions to describe this model. The DPD output is expressed as a linear combination of these basis functions and we show how to directly estimate the LUT entries using least squares. We show how this model achieves lower complexity at similar or better performance compared to polynomial models translated to LUTs with interpolation or models based on LUTs without interpolation whose coefficients are adapted directly. We refer to this model as the direct adaptation of LUTs with interpolation/extrapolation (DLUTI). In this paper we also introduce the composite memory polynomial model: a new polynomial model which is a hybrid between the generalized memory polynomial and the dynamic deviation reduction models. This model is used as a starting point to generate the final LUT-based model. [ABSTRACT FROM PUBLISHER]