Low-frequency Tuning Research Articles

The Emergence of Tuning to Global Shape Properties of Radial Frequency Patterns in the Ventral Visual Pathway.

Radial frequency (RF) patterns, created by sinusoidal modulations of a circle's radius, are processed globally when RF is low. These closed shapes therefore offer a useful way to interrogate the human visual system for global processing of curvature. RF patterns elicit greater responses than those to radial gratings in V4 and more anterior face-selective regions of the ventral visual pathway. This is largely consistent with work on nonhuman primates showing curvature processing emerges in V4, but is evident also higher up the ventral visual stream. Rather than contrasting RF patterns with other stimuli, we presented them at varied frequencies in a regimen that allowed tunings to RF to be derived from 8 human participants (3 female). We found tuning to low RF in lateral occipital areas and to some extent in V4. In a control experiment, we added a high-frequency ripple to the stimuli disrupting the local contour. Low-frequency tuning to these stimuli remained in the ventral visual stream, underscoring its role in global processing of shape curvature. We then used representational similarity analysis to show that, in lateral occipital areas, the neural representation was related to stimulus similarity, when it was computed with a model that captured how stimuli are perceived. We therefore show that global processing of shape curvature emerges in the ventral visual stream as early as V4, but is found more strongly in lateral occipital regions, which exhibit responses and representations that relate well to perception.SIGNIFICANCE STATEMENT We show that tuning to low radial frequencies, known to engage global shape processing mechanisms, was localized to lateral occipital regions. When low-level stimulus properties were accounted for such tuning emerged in V4 and LO2 in addition to the object-selective region LO. We also documented representations of global shape properties in lateral occipital regions, and these representations were predicted well by a proxy of the perceptual difference between the stimuli.

Dendritic synapse geometry optimizes binaural computation in a sound localization circuit.

Clustering of synapses allows neurons to overcome attenuation of electrical signals at dendrites. However, we show in avian binaural coincidence detectors computing interaural time difference for sound localization that clustering of synapses rather promotes the dendritic attenuation but augments the intensity tolerance of the binaural computations. Using glutamate uncaging, we found in the neurons that synapses were clustered at distal dendritic branches. Modeling revealed that this strengthened sublinear integration within a dendritic tree but enabled the integration of signals from different trees when inputs grow stronger, preventing monoaural output and maintaining the dynamic range of binaural computation. The extent of this clustering differed according to dendritic length and frequency tuning of neurons, being most prominent for long dendrites and low-frequency tuning. This ensures binaural spatial hearing for wide intensity and frequency ranges, highlighting the importance of coupling of synapse geometry with dendritic morphology and input frequency in sensory signal processing.

Effect of different magnets and iron-platelets on the low frequency performance of membrane sound absorber

To achieve a compact design for low frequency tunable sound absorption, a membrane sound absorber (MSA) with nonlinear magnetic field is proposed in this paper. By employing a central iron platelet on the membrane, the MSA can be easily tuned by introducing a magnet at a distance from the platelet that can be adjusted. To investigate the low frequency properties of MSA with different magnets and iron-platelets, a series of impedance tube experiments are conducted in detail. The sample absorber has a rear cavity depth of 30 mm, three different magnets were used inside, tested results real that using a strong magnetic field can help broaden the frequency tuning range. Then, results from the MSA with five different sizes of iron plates tuned by one magnet show that the low-frequency tuning range moves to lower with the increase of the area of iron plates.

Quartz-enhanced photoacoustic spectroscopy exploiting low-frequency tuning forks as a tool to measure the vibrational relaxation rate in gas species

We demonstrated that quartz-enhanced photoacoustic spectroscopy (QEPAS) is an efficient tool to measure the vibrational relaxation rate of gas species, employing quartz tuning forks (QTFs) as sound detectors. Based on the dependence of the QTF resonance frequency on the resonator geometry, a wide range of acoustic frequencies with narrow detection bandwidth was probed. By measuring the QEPAS signal of the target analyte as well as the resonance properties of different QTFs as a function of the gas pressure, the relaxation time can be retrieved. This approach has been tested in the near infrared range by measuring the CH4 (nν4) vibrational relaxation rate in a mixture of 1% CH4, 0.15 % H2O in N2, and the H2O (ν1) relaxation rate in a mixture of 0.5 % H2O in N2. Relaxation times of 3.2 ms Torr and 0.25 ms Torr were estimated for CH4 and H2O, respectively, in excellent agreement with values reported in literature.

Terahertz photonic integrated circuit for frequency tuning and power modulation

The quantum cascade laser is a powerful solid-state source of terahertz-frequency radiation. However, integrating multiple photonic functions into a monolithic platform in this frequency range is non-trivial due to the scaling of photonic structures for the long terahertz wavelengths and the low frequency tuning coefficients of the quantum cascade lasers. Here, we have designed a simple terahertz-frequency photonic integrated circuit by coupling a racetrack resonator with a ridge laser in the longitudinal direction to design a notch filter. The transmission properties of this filter structure are dependent on the phase matching and losses in the coupled racetrack and results in a comb of stopband frequencies. We have optimized the comb separation by carefully selecting the cavity dimensions of the racetrack resonator to suppress longitudinal modes in the ridge laser enabling single-mode emission. The emission frequencies and output power from laser are controlled through appropriate control of drive currents to the ridge and the racetrack resonator. The emission frequency is electrically tuned over ∼81 GHz exploiting Stark shift of the gain as a function of drive current at the ridge laser, coinciding with an output power variation of ∼27% of the peak power (at a heat sink temperature of 50 K). The output power from the ridge also varied by ∼30% and the frequency was tuned by a further 10 GHz when the driving conditions at the ridge laser are invariant and the current at the racetrack resonator was varied. To our best knowledge, this is the first report of a frequency engineering, tuning and power modulation of terahertz-frequency quantum cascade lasers using a photonic integrated circuit.

Command-shaping based on impulse response function for dynamic-mode control of internal and external cavities in external-cavity diode laser.

An external-cavity diode laser (ECDL) generally includes low-frequency tuning capability. As the tuning frequency increases, the mechanical vibration of the external-cavity inherent in the ECDL is enhanced, disrupting the mode-matching of the internal and external cavities and considerably reducing the mode-hop-free (MHF) tuning range. In order to implement a wide MHF range with high-frequency tuning, we present an active internal-cavity mode control method with an impulse response function (IRF) shaper for the dynamic mode-matching of the internal and external cavities. After introducing the IRF shaper, experimental results indicate significant improvement in the MHF range with high-frequency tuning. In addition, a maximum wavelength tuning rate of 7.56 THz/s is obtained using an uncoated laser diode with a central wavelength of 785 nm.

Dynamic mode matching of internal and external cavities for enhancing the mode-hop-free synchronous tuning characteristics of an external-cavity diode laser

This paper proposed an external-cavity diode laser (ECDL) that has low-frequency tuning (< 10 Hz) ability using the synchronous tuning principle. However, during high-frequency tuning, the mechanical vibration of the external-cavity system inherent in the ECDL is excited, which will break the mode matching of the internal and external cavities and greatly decrease the mode-hop-free (MHF) tuning range of the ECDL. To obtain a wide MHF range at high-frequency tuning, we used an active internal-cavity mode control method with an inductance–resistance–capacitance (LRC) filter to implement the dynamic mode matching of the internal and external cavities. After using the LRC filter, the experimental results indicated that the MHF tuning range at high-frequency tuning was significantly improved and a maximum wavelength tuning rate of 6.21 THz/s was obtained at tuning frequency of 30 Hz using an uncoated laser diode with a central wavelength of 785 nm.

The Study of Spatial Frequency Channels for Human Visual System

Similar to auditory perception of sound system, color perception of the human visual system also presents a multi-frequency channel property. In order to study the multi-frequency channel mechanism of how the human visual system processes color information, the paper proposed a psychophysical experiment to measure the contrast sensitivities based on 17 color samples of 16 spatial frequencies on CIELAB opponent color space. Correlation analysis was carried out on the psychophysical experiment data, and the results show obvious linear correlations of observations for different spatial frequencies of different observers, which indicates that a linear model can be used to model how human visual system processes spatial frequency information. The results of solving the model based on the experiment data of color samples show that 9 spatial frequency tuning curves can exist in human visual system with each lightness, R–G and Y–B color channel and each channel can be represented by 3 tuning curves, which reflect the “center-around” form of the human visual receptive field. It is concluded that there are 9 spatial frequency channels in human vision system. The low frequency tuning curve of a narrow-frequency bandwidth shows the characteristics of lower level receptive field for human vision system, the medium frequency tuning curve shows a low pass property of the change of medium frequent colors and the high frequency tuning curve of a width-frequency bandwidth, which has a feedback effect on the low and medium frequency channels and shows the characteristics of higher level receptive field for human vision system, which represents the discrimination of details.

Evolutionarily conserved coding properties favour the neuronal representation of heterospecific signals of a sympatric katydid species

To function as a mechanism in premating isolation, the divergent and species-specific calling songs of acoustic insects must be reliably processed by the afferent auditory pathway of receivers. Here, we analysed the responses of interneurons in a katydid species that uses long-lasting acoustic trills and compared these with previously reported data for homologous interneurons of a sympatric species that uses short chirps as acoustic signals. Some interneurons of the trilling species respond exclusively to the heterospecific chirp due to selective, low-frequency tuning and “novelty detection”. These properties have been considered as evolutionary adaptations in the sensory system of the chirper, which allow it to detect signals effectively during the simultaneous calling of the sympatric sibling species. We propose that these two mechanisms, shared by the interneurons of both species, did not evolve in the chirper to guarantee its ability to detect the chirp under masking conditions. Instead we suggest that chirpers evolved an additional, 2-kHz component in their song and exploited pre-existing neuronal properties for detecting their song under masking noise. The failure of some interneurons to respond to the conspecific song in trillers does not prevent intraspecific communication, as other interneurons respond to the trill.

Dual-Band Waveform Generator With Ultra-Wide Low-Frequency Tuning-Range

This paper presents a novel mixed-signal low-power dual-band square/triangular waveform generator (WFG) chip with a wide low-frequency tuning range for medical bio-electric stimulation therapy. It consists of a relaxation oscillator comprising a hysteresis Schmitt trigger and a timing integrator, along with frequency divider (FD) stages and path selector output for driving an electrode from 16 selectable channels. It was fabricated using Global Foundries 8RF-DM 130-nm CMOS process with a supply voltage of ±1 V for the oscillator and +1 V for logic circuits. The WFG provides an output of around 1.5 $\text{V}_{\textrm {p-p}}$ at a nominal low oscillation frequency of 17 kHz using small-size on-chip passive components of values 10 $\text{k}\Omega $ and 10 pF. The WFG core (band I) can be tuned in the range 6.44–1003 kHz through bias current adjustment, while a lower frequency (band II) in the range 0.1 Hz–502 kHz can be provided digitally through a $\div 2$ stage. The power consumption was only 0.457 mW for the WFG and 2.1 mW for the FD circuit while occupying a total silicon area of only 18 $426~\mu \text{m}^{2}$ .

Speech training alters consonant and vowel responses in multiple auditory cortex fields

Speech sounds evoke unique neural activity patterns in primary auditory cortex (A1). Extensive speech sound discrimination training alters A1 responses. While the neighboring auditory cortical fields each contain information about speech sound identity, each field processes speech sounds differently. We hypothesized that while all fields would exhibit training-induced plasticity following speech training, there would be unique differences in how each field changes. In this study, rats were trained to discriminate speech sounds by consonant or vowel in quiet and in varying levels of background speech-shaped noise. Local field potential and multiunit responses were recorded from four auditory cortex fields in rats that had received 10 weeks of speech discrimination training. Our results reveal that training alters speech evoked responses in each of the auditory fields tested. The neural response to consonants was significantly stronger in anterior auditory field (AAF) and A1 following speech training. The neural response to vowels following speech training was significantly weaker in ventral auditory field (VAF) and posterior auditory field (PAF). This differential plasticity of consonant and vowel sound responses may result from the greater paired pulse depression, expanded low frequency tuning, reduced frequency selectivity, and lower tone thresholds, which occurred across the four auditory fields. These findings suggest that alterations in the distributed processing of behaviorally relevant sounds may contribute to robust speech discrimination.

Auditory saccular sensitivity of the vocal Lusitanian toadfish: low frequency tuning allows acoustic communication throughout the year

A novel form of auditory plasticity for enhanced detection of social signals was described in a teleost fish, Porichthys notatus (Batrachoididae, Porichthyinae). The seasonal onset of male calling coincides with inshore migration from deep waters by both sexes and increased female sensitivity to dominant frequencies of male calls. The closely related Lusitanian toadfish, Halobatrachus didactylus, (Batrachoididae, Halophryninae) also breeds seasonally and relies on acoustic communication to find mates but, instead, both sexes stay in estuaries and show vocal activity throughout the year. We investigated whether the sensitivity of the inner ear saccule of H. didactylus is seasonally plastic and sexually dimorphic. We recorded evoked potentials from populations of saccular hair cells from non-reproductive and reproductive males and females in response to 15-945Hz tones. Saccular hair cells were most sensitive at 15-205Hz (thresholds between 111 and 118dB re. 1 μPa). Both sexes showed identical hearing sensitivity and no differences were found across seasons. The saccule was well suited to detect conspecific vocalizations and low frequencies that overlapped with lateral line sensitivity. We showed that the saccule in H. didactylus has major importance in acoustic communication throughout the year and that significant sensory differences may exist between the two batrachoidid subfamilies.

Quadrature Injection-Locked Frequency Dividers Using Dual-Resonance Resonator

This letter studies the property of a divide-by-2 quadrature injection-locked frequency divider (QILFD) with dual-resonance resonator. The QILFD consists of a transformer-coupled quadrature voltage controlled oscillator and two NMOS injectors. The proposed QILFD has been implemented with the TSMC 0.18 μm CMOS technology and the core power consumption is 3.4 mW at the supply voltage of 0.75 V. At the input power of 0 dBm, the low-band and high-band divide-by-2 operation ranges are respectively from 6.3 GHz to 8.2 GHz and 8.1 GHz to 10.3 GHz. The high-frequency band tuning range of free-running QILFD can be measured after the power-on, and the low-frequency band tuning range of free-running QILFD can be measured only after the low-frequency band injection signal is injected to the QILFD.

Coding of Stimuli by Ampullary Afferents inGnathonemus petersii

Weakly electric fish use electroreception for both active and passive electrolocation and for electrocommunication. While both active and passive electrolocation systems are prominent in weakly electric Mormyriform fishes, knowledge of their passive electrolocation ability is still scarce. To better estimate the contribution of passive electric sensing to the orientation toward electric stimuli in weakly electric fishes, we investigated frequency tuning applying classical input-output characterization and stimulus reconstruction methods to reveal the encoding capabilities of ampullary receptor afferents. Ampullary receptor afferents were most sensitive (threshold: 40 μV/cm) at low frequencies (<10 Hz) and appear to be tuned to a mix of amplitude and slope of the input signals. The low-frequency tuning was corroborated by behavioral experiments, but behavioral thresholds were one order of magnitude higher. The integration of simultaneously recorded afferents of similar frequency-tuning resulted in strongly enhanced signal-to-noise ratios and increased mutual information rates but did not increase the range of frequencies detectable by the system. Theoretically the neuronal integration of input from receptors experiencing opposite polarities of a stimulus (left and right side of the fish) was shown to enhance encoding of such stimuli, including an increase of bandwidth. Covariance and coherence analysis showed that spiking of ampullary afferents is sufficiently explained by the spike-triggered average, i.e., receptors respond to a single linear feature of the stimulus. Our data support the notion of a division of labor of the active and passive electrosensory systems in weakly electric fishes based on frequency tuning. Future experiments will address the role of central convergence of ampullary input that we expect to lead to higher sensitivity and encoding power of the system.

Tamoxifen inhibits BK channels in chick cochlea without alterations in voltage-dependent activation

Large-conductance, Ca(2+)-activated, and voltage-gated potassium channels (BK, BK(Ca), or Maxi-K) play an important role in electrical tuning in nonmammalian vertebrate hair cells. Systematic changes in tuning frequency along the tonotopic axis largely result from variations in BK channel kinetics, but the molecular changes underpinning these functional variations remain unknown. Auxiliary beta(1) have been implicated in low-frequency tuning at the cochlear apex because these subunits dramatically slow channel kinetics. Tamoxifen (Tx), a (xeno)estrogen compound known to activate BK channels through the beta-subunit, was used to test for the functional presence of beta(1). The hypotheses were that Tx would activate the majority of BK channels in hair cells from the cochlear apex due to the presence of beta(1) and that the level of activation would exhibit a tonotopic gradient following the expression profile of beta(1). Outside-out patches of BK channels were excised from tall hair cells along the apical half of the chicken basilar papilla. In low-density patches, single-channel conductance was reduced and the averaged open probability was unaffected by Tx. In high-density patches, the amplitude of ensemble-averaged BK current was inhibited, whereas half-activation potential and activation kinetics were unaffected by Tx. In both cases, no tonotopic Tx-dependent activation of channel activity was observed. Therefore, contrary to the hypotheses, electrophysiological assessment suggests that molecular mechanisms other than auxiliary beta-subunits are involved in generating a tonotopic distribution of BK channel kinetics and electric tuning in chick basilar papilla.

Low-frequency tuning in the human vestibular–ocular projection is determined by both peripheral and central mechanisms

We recently reported that a major contribution to the low-frequency tuning and sensitivity of the human vestibular system is the biomechanical properties of the vestibular end-organs. In the current paper, we investigate the contribution of additional mechanisms to low-frequency tuning. We compared the response properties of the vestibular system in 6 human volunteers to trains of 2ms pulses of sound and transmastoid vibration using pulse repetition frequencies of 12.5, 25, 50, 100, 200 and 400Hz. Measurements were made using two separate pathways arising from the vestibular apparatus: to the neck using vestibular evoked myogenic potentials (VEMPs), and to the eyes using ocular vestibular evoked myogenic potentials (OVEMPs). For both sound and vibration the two response pathways produced different tuning to pulse trains. The vestibulo-ocular pathway was characterised by a band-pass tuning with best frequency of 100Hz whereas the vestibulo-collic pathway showed a peak at 400Hz with sound only. These results suggest that properties of the vestibulo-ocular pathway also contribute to the low-frequency tuning that occurs for the OVEMP, in addition to previously reported end-organ effects.

Seismic imaging of basalts at Glyvursnes, Faroe Islands: hunting for future exploration methods in basalt covered areas

Obtaining good sub-basalt seismic images is known to be problematic (Ziolkowski et al., 2003; White et al., 2003). Although the properties of basalts are quite different from those of most sediments Planke (1999) suggested that seismic energy is transmitted through basalt in much the same way as through sediments so the problem of seismic imaging through basalts amounts to the conventional task of separating primary energy from noise, even though the noise including multiples may be considerable. The physical properties of basalt are markedly different from those of the overlying and underlying sediments. Strong reflections due to high impedance contrasts at the top (and bottom) of the basalts leads to significant loss of transmitted seismic energy (Fruehn et al., 2001). Large variations of intrinsic properties along vertical cross-sections of basalt flows have been demonstrated and quantified by analyses of well-logs from wells penetrating successions of flood basalts (Planke, 1994) and from surface mapping (e.g., Self et al., 1998; Thordarson and Self, 1998). This causes the stratigraphic filtering effects of basalt successions to be more severe than that of sediments (Maresh and White, 2005; Shaw et al., 2004). Lateral variations in the thicknesses of sediments interbedded between basalt flows and in the thickness of the upper porous part of basalt flows have been demonstrated by detailed investigations in exposed flood basalts (Self et al., 1998; Thordarson and Self, 1998). The roughness of inter-beds causes 3D scattering of seismic energy, as demonstrated in studies comparing stratigraphic filtering and the effective quality factor, Q, of basalt successions (e.g., White et al., 2005; Shaw et al., 2005; Shaw et al., 2004). Taking these problems into consideration, experiments have been performed in the last decade using: longer offsets (both synthetic aperture, and longer streamers) to improve the signal-to-noise ratio and NMO resolution and to allow processing of post-critical reflections; larger energy sources to increase the general energy level; low-frequency tuning to allow for better penetration through basalts (characterised by low Q values); and shot-by-shot recording of the source signature and combination of OBS and seismic reflection data to improve velocity estimates. In one experiment all of the above-mentioned techniques were applied, providing considerable improvements in sub-basalt imaging relative to previous work (Spitzer and White, 2005; White et al., 2005). An other parameter for seismic acquisition is the orientation of the seismic line relative to the flow direction of the basalt flows (Reshef et al., 2003). However, poor effective transmission of seismic energy, scattering, strong multiple reflections, multiple mode conversions, and low-pass filtering of the energy that propagates through a layer of stacked basalt flows are still hampering routine imaging for petroleum exploration in sediment basins covered by basalts (Maresh and White, 2005). This was demonstrated by the UK164/07- 01 well where the base of a basaltic succession was found 700 m deeper than anticipated from interpretation of seismic reflection data (Archer et al., 2005). In order to obtain imaging quality and detail comparable to those obtained in other sedimentary basins, further improvements are necessary. The SeiFaBa Project (Seismic and petrophysical properties of Faroes Basalts), sponsored by the Sindri group, aims to create data-derived models for the propagation of seismic energy in basalt to provide a basis for better sub-basalt imaging. The project comprises drilling of the Glyvursnes-1 wells near Tórshavn on the Faroe Islands (Figure 1), core analysis for intrinsic physical parameters, recording of VSP and offset-VSP data in the Glyvursnes-1 and Vestmanna-1 wells, and surface seismic wide-angle and reflection data around the Glyvursnes- 1 and Vestmanna-1 wells (Japsen et al., 2005). At both sites these investigations of the elastic properties of basalts are made at a number of different scales. In this paper we present surface seismic reflection data from SeiFaBa experiment at Glyvursnes in the summer of 2003 illustrating that basalts can be imaged effectively using relatively small energy sources (250 g dynamite; 2.6-litre airgun cluster) and that stratigraphic details of flood-basalt constructions can be identified and characterized based on analysis of seismic data and then correlated to well data. We also demonstrate how different acquisition and processing techniques influence the effective frequency content of seismic reflection data and thus the effective propagation through and imaging of the basalts.

Middle ear dynamics in response to seismic stimuli in the Cape golden mole (Chrysochloris asiatica)

The hypertrophied malleus in the middle ear of some golden moles has been assumed to be an adaptation for sensing substrate vibrations by inertial bone conduction, but this has never been conclusively demonstrated. The Cape golden mole (Chrysochloris asiatica) exhibits this anatomical specialization, and the dynamic properties of its middle ear response to vibrations were the subjects of this study. Detailed three-dimensional middle ear anatomy was obtained by x-ray microcomputed tomography (muCT) at a resolution of 12 microm. The ossicular chain exhibits large malleus mass, selective reduction of stiffness and displacement of the center of mass from the suspension points, all favoring low-frequency tuning of the middle ear response. Orientation of the stapes relative to the ossicular chain and the structure of the stapes footplate enable transmission of substrate vibrations arriving from multiple directions to the inner ear. With the long axes of the mallei aligned parallel to the surface, the animal's head was stimulated by a vibration exciter in the vertical and lateral directions over a frequency range from 10 to 600 Hz. The ossicular chain was shown to respond to both vertical and lateral vibrations. Resonant frequencies were found between 71 and 200 Hz and did not differ significantly between the two stimulation directions. Below resonance, the ossicular chain moves in phase with the skull. Near resonance and above, the malleus moves at a significantly larger mean amplitude (5.8+/-2.8 dB) in response to lateral vs vertical stimuli and is 180 degrees out of phase with the skull in both cases. A concise summary of the propagation characteristics of both seismic body (P-waves) and surface (R-waves) is provided. Potential mechanisms by which the animal might exploit the differential response of the ossicular chain to vertical and lateral excitation are discussed in relation to the properties of surface seismic waves.

Feedback and Feedforward Control of Frequency Tuning to Naturalistic Stimuli

Sensory neurons must respond to a wide variety of natural stimuli that can have very different spatiotemporal characteristics. Optimal responsiveness to subsets of these stimuli can be achieved by devoting specialized neural circuitry to different stimulus categories, or, alternatively, this circuitry can be modulated or tuned to optimize responsiveness to current stimulus conditions. This study explores the mechanisms that enable neurons within the initial processing station of the electrosensory system of weakly electric fish to shift their tuning properties based on the spatial extent of the stimulus. These neurons are tuned to low frequencies when the stimulus is restricted to a small region within the receptive field center but are tuned to higher frequencies when the stimulus impinges on large regions of the sensory epithelium. Through a combination of modeling and in vivo electrophysiology, we reveal the respective contributions of the filtering characteristics of extended dendritic structures and feedback circuitry to this shift in tuning. Our results show that low-frequency tuning can result from the cable properties of an extended dendrite that conveys receptor-afferent information to the cell body. The shift from low- to high-frequency tuning, seen in response to spatially extensive stimuli, results from increased wide-band input attributable to activation of larger populations of receptor afferents, as well as the activation of parallel fiber feedback from the cerebellum. This feedback provides a cancellation signal with low-pass characteristics that selectively attenuates low-frequency responsiveness. Thus, with spatially extensive stimuli, these cells preferentially respond to the higher-frequency components of the receptor-afferent input.

Autoparametric resonance of relaxation oscillations

Stable normal mode vibrations in engineering can be undesirable and one of the possibilities for quenching these vibrations is by embedding the oscillator in an autoparametric system by coupling to a damped oscillator. We have the possibility of destabilising the undesirable vibrations by a suitable tuning and choice of coupling parameters. In the case of normal mode vibration derived from a relaxation oscillations we need low-frequency tuning of the attached oscillator. An additional feature is that to make the quenching effective we also have to deform the slow manifold by choosing appropriate coupling; this is illustrated for van der Pol relaxation. A number of numerical experiments have been done and show some interesting phenomena, such as a chaotic attractor and effective quenching.