Frequency Sensitivity Research Articles

Enhancing the Psychometric Properties of the Iowa Gambling Task Using Full Generative Modeling.

Poor psychometrics, particularly low test-retest reliability, pose a major challenge for using behavioral tasks in individual differences research. Here, we demonstrate that full generative modeling of the Iowa Gambling Task (IGT) substantially improves test-retest reliability and may also enhance the IGT's validity for use in characterizing internalizing pathology, compared to the traditional analytic approach. IGT data was collected across two sessions, one month apart. Our full generative model incorporated (1) the Outcome Representation Learning (ORL) computational model at the person-level and (2) a group-level model that explicitly modeled test-retest reliability, along with other group-level effects. Compared to the traditional 'summary score' (proportion good decks selected), the ORL model provides a theoretically rich set of performance metrics (Reward Learning Rate , Punishment Learning Rate , Win Frequency Sensitivity , Perseveration Tendency , Memory Decay ), capturing distinct psychological processes. While test-retest reliability for the traditional summary score was only moderate (, BCa 95% CI [.04, .63]), test-retest reliabilities for ORL performance metrics produced by the full generative model were substantially improved, with test-retest correlations ranging between for the five ORL parameters. Further, while summary scores showed no substantial associations with internalizing symptoms, ORL parameters were significantly associated with internalizing symptoms. Specifically, Punishment Learning Rate was associated with higher self-reported depression and Perseveration Tendency was associated with lower self-reported anhedonia. Generative modeling offers promise for advancing individual differences research using the IGT, and behavioral tasks more generally, through enhancing task psychometrics.

Diagnostic test accuracy for COVID-19: systematic review and meta-analysis protocol.

ObjectiveAccurate diagnosis of COVID-19 infection is paramount to initiating appropriate measures for reducing spread. We aim to conduct a systematic review and meta-analysis, augmented by linked electronic health records, to assess the diagnostic test accuracy for COVID-19. ApproachWe will search the following databases from November 2019 to February 2022: MEDLINE (PubMed), Embase, and Scopus, as well as reference lists of eligible studies and review articles. Keywords will relate to COVID-19 and diagnostic testing. Eligible studies will use an appropriate study design (e.g. prospective and retrospective cohort and case-control) to assess the accuracy of any COVID-19 diagnostic test (including thoracic imaging, mass spectrometry, and serological tests) in all healthcare and community settings. Studies of participants under 18 will be excluded. Data will be extracted using a piloted extraction form and bias will be assessed using the QUADAS-2 tool. ResultsMain outcomes will include frequency statistics, sensitivity and specificity, and positive and negative predictive value. Paired forest plots will be used to illustrate sensitivity and specificity across studies. We will pool data on sensitivity and specificity in a Bayesian framework using a bivariate random-effects logistic regression model, where appropriate. Uncertainty in the estimates will be represented using 95% credible intervals. A comparative framework will be developed to allow assessment of the comparative accuracy of diagnostic tests. Subgroup analyses will be undertaken for time since onset of symptoms, setting (including community and secondary care testing), and reference standard, where appropriate. ConclusionResults of this review will be combined with routinely collected electronic health records from the DECOVID database to inform relationships between tests and subgroups for healthcare decision-making. New methodology developed as part of this review will be generalizable to the evaluation of diagnostic test accuracy in other diseases.

Development of low frequency and high sensitivity fiber optic accelerometer based on multi-stage flexure hinges

In order to reduce the stiffness of the flexure hinges, a low-frequency fiber Bragg grating (FBG) accelerometer based on multi-stage flexure hinges is designed. According to the series–parallel connection theory of springs, the acceleration response and anti-interference characteristics of the accelerometer are experimentally studied. The experimental results shows that the accelerometer with multi-stage hinges has a wide flat frequency band and high sensitivity. The resonant frequency is 84.2 Hz, the response sensitivity of the external vibration signal is 927.21 pm/G in the range of 1–60 Hz and the lateral interference degree is 5.8 %. It shows that the acceleration sensing performance of the accelerometer is good. On this basis, changing the hinge radius, thickness or the size of the mass block can further expand the measurement range of the accelerometer, which is expected to be applied in the field of low-frequency oil and gas seismic exploration.

Comprehensive Engineering Frequency Domain Analysis and Vibration Suppression of Flexible Aircraft Based on Active Disturbance Rejection Controller.

The crash of an aircraft with an almost vertical attitude in Wuzhou, Guangxi, China, on 21 March 2022, has caused a robust discussion in the civil aviation community. We propose an active disturbance rejection controller (ADRC) for suppressing aeroelastic vibrations of a flexible aircraft at the simulation level. The ADRC has a relatively simple structure and it has been proved in several fields to provide better control than the classical proportional-integral-derivative (PID) control theory and is easier to translate from theory to practice compared with other modern control theories. In this paper, the vibration model of the flexible aircraft was built, based on the first elastic vibration mode of the aircraft. In addition, the principle of ADRC is explained in detail, a second-order ADRC was designed to control the vibration model, and the system’s closed-loop frequency domain characteristics, tracking effect and sensitivity were comprehensively analyzed. The estimation error of the extended state observer (ESO) and the anti-disturbance effect were analyzed, while the robustness of the closed-loop system was verified using the Monte Carlo method, which was used for the first time in this field. Simulation results showed that the ADRC suppressed aircraft elastic vibration better than PID controllers and that the closed-loop system was robust in the face of dynamic parameters.

Acoustic Radiation Study of a Box Girder Viaduct Considering the Frequency-Dependent Viscoelasticity of the Rail Pad

In order to investigate the mechanism of the frequency-dependent viscoelasticity of the rail pad on the acoustic radiation characteristics of a box girder viaduct, this study establishes a high-order model of its dynamic parameters to reveal the frequency-varying viscoelasticity of the rail pad, and establishes a vehicle–track–viaduct vertical coupling model. Finally, the acoustic radiation characteristics of a box girder viaduct are analyzed by combining the finite element method and the boundary element theory. The results show that the S-stiffness and D-stiffness of the rail pad increase with the increase in frequency, and the frequency sensitivity of the S-stiffness is greater than that of the D-stiffness. The high-order characterization model of the dynamic parameters of the rail pad has a good fitting effect. The main influence frequency band of the frequency variable viscoelasticity of the rail pad on the wheel–rail force and the equivalent discrete spring force of the sliding layer is 30–90 Hz, resulting in the shift of the dominant frequency to a high frequency by 4 Hz. We consider that the frequency-varying viscoelasticity of the rail pad will cause the dominant frequency of the acoustic pressure level of the field point to shift to a high frequency of 4–6 Hz, which has the greatest influence on the sound pressure level of each field point at the Peak Frequency Point of Insertion Loss (PFPIL), and the influence degree is consistent, resulting in the maximum value of the total sound pressure level of the surface field increasing by 4.1 dB. Without considering the frequency-varying viscoelasticity of the rail pad, the sound pressure level of each field point at 20–53 Hz will be overestimated and the sound pressure level of each field point in the 53–100 Hz frequency band will be underestimated. The panel sound power level contribution coefficient of the box girder is obviously different at different frequency points.

Doppler shift compensation performance in Hipposideros pratti across experimental paradigms

A central aim of neuroethological research is to discover the mechanisms of natural behaviors in controlled laboratory studies. This goal, however, comes with challenges, namely the selection of experimental paradigms that allow full expression of natural behaviors. Here, we explore this problem in echolocating bats that evolved Doppler shift compensation (DSC) of sonar vocalizations to yield close matching between echo frequency and hearing sensitivity. We ask if behavioral tasks influence the precision of DSC in Pratt’s roundleaf bat, Hipposideros pratti, in three classic laboratory paradigms evoking audio-vocal adjustments: Stationary bats listening to echo playbacks, bats transported on a moving pendulum, and bats flying freely. We found that experimental conditions had a strong influence on the expression of the audiovocal frequency adjustments in bats. H. pratti exhibited robust DSC in both free-flying and moving-pendulum experiments but did not exhibit consistent audiovocal adjustments in echo playback experiments. H. pratti featured a maximum compensation magnitude of 87% and a compensation precision of 0.27% in the free flight experiment. Interestingly, in the moving pendulum experiment H. pratti displayed surprisingly high-precision DSC, with an 84% maximum compensation magnitude and a 0.27% compensation precision. Such DSC performance places H. pratti among the bat species exhibiting the most precise audio-vocal control of echo frequency. These data support the emerging view that Hipposiderid bats have a high-precision DSC system and highlight the importance of selecting experimental paradigms that yield the expression of robust natural behaviors.

Series Arc Fault Detection Sensor Based on an ABS Rogowski Coil in Medium Voltage

Three types of Rogowski coils were designed and constructed by utilising 3D printing technology: RC1, RC2, and RC3, with the sensors having the same geometrical dimensions but varying number of turns: 20, 50, and 100 respectively. To verify the feasibility and effectiveness of the proposed sensors, a series arc fault generator was set up and high voltage of up to 3-kV was injected. The analysis of the Fast Fourier Transform (FFT) was done by using MATLAB to determine frequency and voltage amplitude. From the analysis, it was determined that the higher the number of turns, the greater the sensitivity. The resonance frequency (MHz) dropped significantly as the number of turns increased. Furthermore, sensor features such as frequency bandwidth and sensitivity are affected by the number of turns, which was thoroughly investigated in this study. The Rogowski coil was created to detect the high frequency component of the series arc fault signal. All the designed sensors reliably detect the series arc fault signal, according to the experimental results.

Evaluation of Differential Sensitivity for Frequency, Intensity, and Duration in Individuals with Hypertension

Abstract Objective Hypertension is a condition in which the blood vessels have persistently raised pressure. The damage of the cochlea is due to the loss of sensitive hair cells in the inner ear or the damage to the eighth cranial nerve. When the cochlea is damaged, the functioning abilities such as coding, differentiation, and temporal processing abilities will be affected. Hence, there might be deficits in differential sensitivity in individuals with hypertension. The aim of this article was to study the effect of hypertension on differential sensitivity as there is limited literature in this area. Method Thirty participants were included in the study and classified into two groups: group I as individuals with hypertension and group II as individuals with normal blood pressure in the age range of 25 to 45 years. Psychophysical tests like frequency, intensity, and time discrimination tests were performed using the maximum likelihood procedure (MLP) toolbox, which implements a maximum likelihood procedure for threshold estimation in MATLAB. Results In all the three test conditions, the scores were significantly poorer in individuals with hypertension compared with individuals of the normal at all the frequencies such as 500 Hz, 1,000 Hz, 2,000 Hz, and 4,000 Hz. Conclusion This could be because of reduced frequency selectivity and poor temporal coding as well as due to difficulty responding to rapid change in the envelope of sound over time because of cochlear and neural damage in individuals with hypertension.

Tunable surface plasmon resonance sensor based on graphene-coated photonic crystal fiber in terahertz.

A terahertz surface plasmon resonance (SPR) sensor is designed based on photonic crystal fiber (PCF). Graphene is selectively coated in the cladding hole of the PCF and used as plasmonic material. The coupling mechanism, loss properties, tunability, and refractive index sensing performance of the designed SPR sensor are investigated using the finite element method. The peak of the loss spectrum corresponding to the SPR frequency can be dynamically tuned by adjusting graphene's chemical potential, and a tuning sensitivity of 767.5 GHz/eV is obtained. The SPR frequency red shifts linearly with an increase in the refractive index of analyte from 1.0 to 1.5. An average frequency sensitivity of 208.14 GHz/RIU is obtained. This research provides theoretical guidance for the design of terahertz in-fiber SPR sensors and filters.

Super Directional Antenna—3D Phased Array Antenna Based on Directional Elements

This paper describes an antenna design approach for achieving super directivity in an AESA (Active Electronic Scanned Array) radar using an unconventional 3D phased array (PA) antenna concept based on directional Yagi–Uda elements. The proposed scheme is shown to have a wider scanning feature, with higher directivity in comparison to the same geometry dipole array without increasing the element number. The antenna’s microwave design includes an antipodal Yagi–Uda antenna element that is implemented efficiently on a microstrip PCB using a balun (balance–unbalance)-fed network. This type of antenna is valuable in restricted aperture scans for achieving a narrow antenna beam that increases the angular resolution and measurement precision of tracked targets and also enlarges the detection range or, alternatively, achieves the same performance with a lower number of elements—meeting the goal of low-cost production. The notable result of the high antenna directivity was obtained by both the element and the array architecture, which allowed for improvements in the Array Factor (AF) directivity by increasing the element’s spacing and broadening the scan sector, achieved via the suppression of the element’s Grating Lobe (GL). Another important benefit of this antenna design is the superior coupling reduction caused by its enlarged element distances, which are very significant in electronic scans. An outstanding opportunity to exploit this low coupling can be found in separated MIMO radar architecture. Other benefits of this design’s architecture are the support of a combined module and antenna on a unified board thanks to the End-Fire radiation pattern, its low frequency sensitivity, and its low-cost manufacturing.

Hybrid electromagnetic shunt damper with Coulomb friction and negative impedance converter

Electromagnetic shunt damper (EMSD) offers flexible tunability of linear damping. The low damping force-to-mass ratio of the EMSD, however, hinders those applications which require large damping force. Adding a negative impedance shunt in EMSD circuit can increase its damping force and broaden its effective frequency range at the expense of causing possible instabilities in the control circuit. On the other hand, Coulomb friction damper (FD) can offer a higher damping force-to-mass ratio than EMSD but it is difficult to be precisely controlled due to its nonlinear characteristics and excessive frequency sensitivity. This paper examines, both theoretically and experimentally, two types of hybrid dampers: one combining an EMSD and a Coulomb friction damper (EMSD+FD), and the other EMSD with a voltage negative impedance converter (EMSD+VNIC). Through proper control of the additional damping arising from FD and VNIC, the problem of unstable ESMD+VNIC and the excessive frequency sensitivity of the FD are alleviated. A prototype of EMSD+VNIC+FD is built and tested. The damping force provided by the FD in the prototype is varied by adjusting the normal force applied by a compression spring, while that from the EMSD+VNIC is controlled by adjusting the shunt circuit impedance with a variable resistor. The maximized tunability of the two enhancement methods provides a ninefold increase of the tunable damping range and a sixfold increase of the damping force-to-mass ratio of the EMSD. The proposed EMSD+VNIC+FD is finally applied and tested experimentally to achieve H∞ optimization of a ground-hooked dynamic vibration absorber for the minimization of resonant vibration of a single-degree-of-freedom system.

Numerical study of in situ acoustic emission monitoring for small-scale hydraulic fracturing

Abstract Reservoir monitoring is necessary to achieve safe hydrocarbon extraction. It requires monitoring small acoustic emission (AE) events, assisting in determining the exact location, extension and direction of potential damage as early as possible. However, microcracks cannot be detected by the microseismic monitoring networks due to the limitations of frequency range and sensitivity. In contrast, the in situ AE monitoring system extends the detection range to higher frequencies and can detect very small deformation processes with high resolution and sensitivity. It provides detailed insights into ongoing deformation processes. However, the receivers of an in situ AE monitoring system need to be very close to hydraulic fracturing experiments due to the fast decay of high-frequency signals. In this work, by constructing four in situ AE monitoring models, the imaging effects of the interferometric imaging method for three different kHz-level frequency sources at different distances and orientations relative to the monitoring well are investigated. The numerical results show that: the higher the source frequency, the higher the imaging resolution; when the vertical orientation coverage of the source by the monitoring system is incomplete, the closer the source to the borehole axis, the worse the imaging resolution and location accuracy; when the vertical orientation coverage of the source by the monitoring system is complete, the imaging resolution and location accuracy are both improved, especially when the vertical azimuthal coverage angle is large. The integrity of the orientation coverage of the source by the monitoring system plays a critical role in improving source location accuracy.

Sound Induced Vibrations Deform the Organ of Corti Complex in the Low-Frequency Apical Region of the Gerbil Cochlea for Normal Hearing : Sound Induced Vibrations Deform the Organ of Corti Complex.

Human speech primarily contains low frequencies. It is well established that such frequencies maximally excite the cochlea near its apex. But, the micromechanics that precede and are involved in this transduction are not well understood. We measured vibrations from the low-frequency, second turn in intact gerbil cochleae using optical coherence tomography (OCT). The data were used to create spatial maps that detail the sound-evoked motions across the sensory organ of Corti complex (OCC). These maps were remarkably similar across animals and showed little variation with frequency or level. We identify four, anatomically distinct, response regions within the OCC: the basilar membrane (BM), the outer hair cells (OHC), the lateral compartment (lc), and the tectorial membrane (TM). Results provide evidence that active processes in the OHC play an important role in the mechanical interplay between different OCC structures which increases the amplitude and tuning sharpness of the traveling wave. The angle between the OCT beam and the OCC makes that we captured radial motions thought to be the effective stimulus to the mechano-sensitive hair bundles. We found that TM responses were relatively weak, arguing against a role in enhancing mechanical hair bundle deflection. Rather, BM responses were found to closely resemble the frequency selectivity and sensitivity found in auditory nerve fibers (ANF) that innervate the low-frequency cochlea.

Optimization Configuration of Grid-Connected Inverters to Suppress Harmonic Amplification in a Microgrid

This paper provides insight into the optimal configuration scheme of the grid-connected inverters based on harmonic amplification suppression. The connection of the inverters changes the natural resonance frequencies of the grid. Hence, a reasonable configuration of grid-connected inverters can optimize the impedance distribution and shift the natural resonance frequencies to frequency bands farther away from the harmonic sources. We proposed a scheme of site selection and determination of the number of inverters to suppress harmonic amplification. The resonance frequencies and modal frequency sensitivities (MFSs) were obtained by the resonance modal analysis (RMA). Moreover, the concepts of security region and insecurity region of resonance frequency were illustrated. The grid-connected sites can be obtained by calculating the participation factors (PFs) of the resonance frequencies in the insecurity region. Furthermore, the optimal number was determined by building the Norton equivalent circuit of the inverter and evaluating the output impedance at each frequency. Finally, simulations in Matlab/Simulink based on a modified IEEE-9 bus microgrid were utilized to verify the effectiveness of the proposed scheme.

High-Sensitive Parity-Time Symmetric Oscillator in Coupled Transmission Lines With Nonlinear Gain

A scheme for generating oscillations based on an exceptional point of degeneracy (EPD) is proposed in two-coupled resonators made of two coupled transmission lines terminated on balanced gain and loss, exhibiting a double pole. The EPD is a point in the parameter space of the system at which two or more eigenmodes coalesce in both their eigenvalues (here, resonance frequencies) and eigenvectors. We show that a finite-length single transmission line terminated with gain and loss possesses no degeneracy point, whereas second-order EPDs are enabled in two finite-length coupled transmission lines (CTLs) terminated with balanced gain and loss. We demonstrate the conditions for EPDs to exist for three different termination configurations with balanced gain and loss, and show the eigenfrequency bifurcation at the EPD following the fractional power expansion series related to the Puiseux series. We study the oscillatory regime of operation assuming the gain element is nonlinear, and the extreme sensitivity of the degenerate self-oscillation frequency to perturbations and how it compares with the sensitivity of the linear-gain case. Finally, we show that the sensitivity of the EPD-CTL resonator is much higher than the one of a single-TL resonator. The very sensitive EPD based oscillator can be used as sensors when very small variations in a system shall be detected.

PD Flexible Built-In High-Sensitivity Elliptical Monopole Antenna Sensor.

In view of the insufficient signal detection sensitivity of Gas Insulated Switchgear (GIS), partial discharge (PD), ultra-high frequency (UHF), and failure to conform with GIS surface structure when the existing rigid stereo structure UHF sensor is built in, this paper, using rectangular patch antenna equivalent technique, trapezoidal ground plane technique, and coplanar waveguide (CPW) feed line index asymptotic linearization technique, conducts research on a flexible built-in high-sensitivity elliptic monopole antenna. The flexible antenna, with a thickness of only 0.28 mm, can be kept at a voltage standing wave ratio (VSWR) of less than three in the 300 MHz to 3 GHz band under the curvature radius of 0, 100, 300, and 500 mm, and at less than two in the 650 MHz to 3 GHz band. Through the true 220 kV-GIS partial discharge experimental platform built to analyze the high frequency electromagnetic wave detection performance of the built-in flexible antenna, it is shown that the flexible built-in high-sensitivity elliptical monopole antenna designed in this paper can effectively detect the characteristic signals of high-frequency electromagnetic waves emitted by partial discharges with an average discharge amount below 10 pC.

A mechanically coupled three degree-of-freedom resonator with tunable stiffness sensitivity

This paper reports a novel three degree-of-freedom (DoF) mechanical-coupled resonator whose mechanical system is a combination of a normal dual mass resonator (DMR) and an amplified dual mass resonator (ADMR). The mode localization phenomenon is firstly observed between the DMR mode (the anti-phase mode of DMR) and the ADMR mode (the anti-phase mode of ADMR). The resonant frequencies of the DMR and ADMR modes can be tuned to an identical value thanks to the unique structure design so that the amplitude ratio can be highly sensitive to the structural perturbation. The ADMR mode can approach the DMR mode and the amplitude ratio sensitivity can be enhanced by adjusting the inner stiffness, which largely affects the ADMR mode frequency while slightly influences the DMR mode frequency. Using the proposed triple-mass resonator scheme, it is not necessary to use an extremely weak coupling spring, which is advantageous for practical uses. The measurement results showed the as-fabricated frequency difference and sensitivity was 110 Hz and 210, respectively. The frequency difference could be effectively minimized to less than 0.2 Hz, and the sensitivity could be significantly enhanced to be 59922 by electrostatically softening the inner stiffness.

Unbalanced bidirectional radial stiffness gradients within the organ of Corti promoted by TRIOBP

Hearing depends on intricate morphologies and mechanical properties of diverse inner ear cell types. The individual contributions of various inner ear cell types into mechanical properties of the organ of Corti and the mechanisms of their integration are yet largely unknown. Using sub-100-nm spatial resolution atomic force microscopy (AFM), we mapped the Young's modulus (stiffness) of the apical surface of the different cells of the freshly dissected P5-P6 cochlear epithelium from wild-type and mice lacking either Trio and F-actin binding protein (TRIOBP) isoforms 4 and 5 or isoform 5 only. Variants of TRIOBP are associated with deafness in human and in Triobp mutant mouse models. Remarkably, nanoscale AFM mapping revealed unrecognized bidirectional radial stiffness gradients of different magnitudes and opposite orientations between rows of wild-type supporting cells and sensory hair cells. Moreover, the observed bidirectional radial stiffness gradients are unbalanced, with sensory cells being stiffer overall compared to neighboring supporting cells. Deafness-associated TRIOBP deficiencies significantly disrupted the magnitude and orientation of these bidirectional radial stiffness gradients. In addition, serial sectioning with focused ion beam and backscatter scanning electron microscopy shows that a TRIOBP deficiency results in ultrastructural changes of supporting cell apical phalangeal microfilaments and bundled cortical F-actin of hair cell cuticular plates, correlating with messenger RNA and protein expression levels and AFM stiffness measurements that exposed a softening of the apical surface of the sensory epithelium in mutant mice. Altogether, this additional complexity in the mechanical properties of the sensory epithelium is hypothesized to be an essential contributor to frequency selectivity and sensitivity of mammalian hearing.

Low-Phase-Noise CMOS Relaxation Oscillators for On-Chip Timing of IoT Sensing Platforms

The design of low-phase-noise fully integrated frequency references is often a critical aspect in the development of low-cost integrated circuits for communication interfaces, sensing platforms, and biomedical applications. This work first discusses relaxation oscillator topologies and design approaches aimed at minimizing the phase noise; then, a single-comparator low-phase-noise RC relaxation oscillator is proposed, featuring a novel comparator self-threshold-adjustment technique. The oscillator was designed for a 10 MHz oscillation frequency. Electrical simulations performed on a 0.18 μm CMOS design confirmed that the proposed technique effectively rejects the flicker component of the comparator noise, allowing for a 152 dBc/Hz figure of merit at a 1 kHz offset frequency. The standard deviation of the jitter accumulated across 10k oscillation cycles is lower than 4 ns. The simulated current consumption of the circuit is equal to 50.8 μA with a 1.8 V supply voltage. The temperature sensitivity of the oscillation frequency is also notably low, as its worst-case value across process corners is equal to −20.8 ppm/°C from −55 °C to 125 °C.

Melanopsin photoreception differentially modulates rod-mediated and cone-mediated human temporal vision

SummaryTo evaluate the nature of interactions between visual pathways transmitting the slower melanopsin and faster rod and cone signals, we implement a temporal phase summation paradigm in human observers using photoreceptor-directed stimuli. We show that melanopsin stimulation interacts with and alters both rod-mediated and cone-mediated vision regardless of whether it is perceptually visible or not. Melanopsin-rod interactions result in either inhibitory or facilitatory summation depending on the temporal frequency and photoreceptor pathway contrast sensitivity. Moreover, by isolating rod vision, we reveal a bipartite intensity response property of the rod pathway in photopic lighting that extends its operational range at lower frequencies to beyond its classic saturation limits but at the expense of attenuating sensitivity at higher frequencies. In comparison, melanopsin-cone interactions always lead to facilitation. These interactions can be described by linear or probability summations and potentially involve multiple intraretinal and visual cortical pathways to set human visual contrast sensitivity.