Combining ultra-high-field fMRI adaptation and computational modelling to estimate neuronal frequency selectivity in human auditory cortex

Frequency selectivity is a ubiquitous property of auditory neurons. Measuring it in human auditory cortex may be crucial for understanding common auditory deficits, but current non-invasive neuroimaging techniques can only measure the aggregate response of large populations of cells, thereby overestimating tuning width. Here we attempted to estimate neuronal frequency tuning in human auditory cortex using a combination of fMRI-adaptation paradigm at 7T and computational modelling. We measured the BOLD response in the auditory cortex of eleven participants to a high frequency (3.8 kHz) probe presented alone or preceded by adaptors at different frequencies (0.5 to 3.8 kHz). From these data, we derived both the response tuning curves (the BOLD response to adaptors alone as a function of adaptor frequency) and adaptation tuning curves (the degree of response suppression to the probe as a function of adaptor frequency, assumed to reflect neuronal tuning) in primary and secondary auditory cortical areas, delineated in each participant. Results suggested the existence of both frequency-independent and frequency-specific adaptation components, with the latter being more frequency-tuned than response tuning curves. Using a computational model of neuronal adaptation and BOLD non-linearity in topographically-organized cortex, we demonstrate both that the frequency-specific adaptation component overestimates the underlying neuronal frequency tuning and that frequency-specific and frequency-independent adaptation component cannot easily be disentangled from the adaptation tuning curve. By fitting our model directly to the response and adaptation tuning curves, we derive a range of plausible values for neuronal frequency tuning. Our results suggest that fMRI adaptation is suitable for measuring neuronal frequency tuning properties in human auditory cortex, provided population effects and the non-linearity of BOLD response are taken into account.

Plasmon resonances management of meta-mirror for combining radar cross section (RCS) reduction and specular reflection with frequency selectivity

In this paper using Plasmon Resonances Management (PRM), a bi-functional meta-mirror is proposed in which, the meta-mirror can obtain two opposite properties in two different frequency ranges. In this method, an anisotropic unit cell with polarization conversion property is modified to have two plasmon resonances in both symmetric and anti-symmetric planes in a specific frequency. This allows the unit cell to have the property of unchanged polarization in that frequency. The meta-mirror is composed of this modified unit cell and its mirror as a chessboard arrangement and the incident wave on the meta-mirror is reflected as in-phase in that specific frequency i.e. specular reflection, while as out-of-phase in other frequencies i.e. RCS reduction. The designed meta-mirror in this paper demonstrates the RCS reduction in two side-bands from 4 to 9 GHz and 10.8 to 14.8 GHz while behaving as a specular reflection in the frequency around 10 GHz.

Implementation of Efficient Reconfigurable FIR Filter With Control Logic for 5G Applications

Filters are used to achieve frequency selectivity on the spectrum of input signal. Due to the stability of FIR filters, they are used in most of the applications. In the conventional FIR filters the frequency band is fixed and can‟t be changed once it is designed. Hence there is a necessity of an FIR filter with auto adjustment of band width. The design of FIR filter requires more number of filter coefficients to get the desired bandwidth specification. This results in a large slice for FPGA implementation. Here it is proposed a state machine to select different FIR filters with the designated set of coefficients. Each FIR filter is having different set of coefficients and based on the frequency of the clock signal the FIR filter is selected. Therefore frequency selectivity can be achieved. The Proposed method is to implement Reconfigurable FIR Filter with control logic for auto adjustment of fre-quency selections to achieve better band width requirements. The filter order is initially selected as 4 and presented the simulation results. The order of the filter(n) increased to 24 for verifying the bandwidth selection. The proposed architecture is compared with the existing architecture with 16bits and 11taps. Simulation results presented are verified using Xilinx ISE design suite 14.7. Total number of 4 input LUTs utilized are 630 for n=24. Power consumed by the overall design is 195mW.

Spatial and Temporal Selectivity of Translational Glass Patterns Assessed With the Tilt After-Effect

Glass patterns (GPs) have been widely employed to investigate the mechanisms underlying processing of global form from locally oriented cues. The current study aimed to psychophysically investigate the level at which global orientation is extracted from translational GPs using the tilt after-effect (TAE) and manipulating the spatiotemporal properties of the adapting pattern. We adapted participants to translational GPs and tested with sinewave gratings. In Experiment 1, we investigated whether orientation-selective units are sensitive to the temporal frequency of the adapting GP. We used static and dynamic translational GPs, with dynamic GPs refreshed at different temporal frequencies. In Experiment 2, we investigated the spatial frequency selectivity of orientation-selective units by manipulating the spatial frequency content of the adapting GPs. The results showed that the TAE peaked at a temporal frequency of ∼30 Hz, suggesting that orientation-selective units responding to translational GPs are sensitive to high temporal frequencies. In addition, TAE from translational GPs peaked at lower spatial frequencies than the dipoles’ spatial constant. These effects are consistent with form-motion integration at low and intermediate levels of visual processing.