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Biomedical subjects

F Grandori

Publications and source records attributed to F Grandori.

67 records · Page 4Linked to original sources
PubMed1976

Electrocochleography by mathematical modelling.

The aim of this work is to critically review some of the classical electrocochleographic methods in accordance with the systems theory: (a) in describing, by means of mathematical models, the different parts of the auditory system concerned in the generation of stimulus-evoked signals; and: (b) in comparing the outputs of these models with the measurements of the cochlear potentials. It must be stated clearly that we realise that many of the conclusions drawn could be criticised, it is hoped that future research in the field with be stimulated by this work.

Adaptation, Physiological↗
PubMed1976

Do efferent fibres to hair cells intervene in acoustic stimulus peripheral coding?

The functional roles suggested for Olivo-Cochlear Bundle (OCB) fibres innervating auditory receptors never received a fully convincing demonstration. Assuming that efferent fibres effects, at the level of hair cells, are inhibitory with regard to single auditory nerve fibre activity, a mathematical model of the peripheral auditory system is proposed in which the presence of the descending pathway is taken into account. Computer simulation of the model accounts for most of the salient features of the patterns of activity of single cochlear nerve fibres. In the light of the model predictions, the influence of OCB fibres on peripheral receptors is assumed to act in the direction of improving the signal-to-noise ratio, as a first step of information processing.

Acoustic Stimulation↗
PubMed1975

Compound action potential and single acoustic nerve fibres activity generation: an equivalent neuron approach.

The peripheral acoustic system can be easily subdivided into three distinct subsystems: a mechanical one (middle ear and basilar membrane), the set of mechanical-to-neural transducers (the inner and outer hair cells) and the neural part. The functional behaviour of the external and middle ear is well known, but the processes concerned with the transduction of mechanical motion into neural activity are still under investigation. Actually the mechanism of transmission of information concerning acoustic stimuli to the central nervous pathways is not clearly known. On the basis of physiological knowledge, a mathematical model reproducing the pattern of activity of the acoustic nerve, in response to the most typical acoustic stimuli, is proposed. This has been simulated on a digital computer.

Action Potentials↗
PubMedDate not supplied

Magnetic stimulation of the nervous system: induced electric field in unbounded, semi-infinite, spherical, and cylindrical media.

Knowledge of the electric field that is induced in the brain or the limbs is of importance in magnetic stimulation of the nervous system. Here, an analytical model based on the reciprocity theorem is used to compare the induced electric field in unbounded, semi-infinite, spherical, and cylinder-like volume conductors. Typical stimulation coil arrangements are considered, including the double coil and various orientations of the single coil. The results can be used to determine when the influence of the boundaries is negligible enough to allow the use of more simplified geometries.

Brain↗
PubMedDate not supplied

Interpretation of the whole-nerve action potential off-effect in response to tone bursts.

The growth of an off-effect in the whole-nerve action potential (AP) at the end of a tone burst is explained by means of some fundamental laws of systems theory applied to the available knowledge of the mechanisms of generation of the AP. The dependence of the amplitude and of the shape of the off-AP on the burst paradigms (frequency, amplitude and phase) is successfully predicted on the ground of a simple model for the cochlear events.

Acoustic Stimulation↗
PubMedDate not supplied

Optimal band pass filtering of transient evoked otoacoustic emissions in neonates.

This paper investigated the performance of an optimal bandpass filtering technique to effectively identify click evoked otoacoustic emissions in neonates. The frequency response of the filter was optimized by maximizing the correlation coefficient between two replicate recordings (reproducibility). The optimal cut-off frequencies were also set by controlling the maximum energy loss after filtering to stop the crucial response contents being filtered along with the noise. As an additional constraint, the cut-off frequencies were forced to be outside the range of 1.6 to 4.2 kHz to avoid (in a response identification task) the spontaneous otoacoustic emissions from polarizing the cut-offs and thereby filtering fundamental frequency components, thus leading to an erroneous response classification. The best performance of the optimal filter in terms of increasing the post-filtering reproducibility was obtained when the procedure was applied to recordings whose reproducibility before filtering ranged between 60 and 80 per cent, i.e. for responses classified in most cases as partial pass.

Acoustic Stimulation↗
PubMedDate not supplied

Evaluation of click evoked otoacoustic emissions in newborns: effects of time-windowing.

The objective of this study was to investigate the effects of time-windowing on click evoked otoacoustic emissions (CEOAEs); 466 CEOAEs from full-term babies were considered. Data were acquired according to the default ILO88 response window (2.5-20 ms). Because CEOAEs are time-varying signals, each emission was analysed by means of the wavelet transform (WT), a technique which allows a simultaneous representation of the time and frequency features of a signal. By means of the WT it was possible to extract the temporal pattern of the elementary frequency components of the compound emissions. The effects of time-windowing were evaluated on each single emission component: rms and correlation values were computed from six 2.5-ms long time windows in the 2.5-17.5 ms range. Results indicated that both rms and correlation were not constant with time but reached a maximum in specific time-windows, depending on the frequency of the component. For low-frequency components, the correlation typically had a maximum in the interval 10-12.5 ms, whereas high-frequency components had a maximum around 5 ms. Above 12.5 ms, the correlation was greatly decreased for all frequency components. As a result, the comparison between the performance of the default ILO88 window (2.5-20 ms) and the window 2.5-12.5 ms showed that for all frequencies in the 1.5-6 kHz range there was a statistically significant improvement in the correlation. No improvement was observed for frequencies below 1.5 kHz because of their contamination by the residual background noise.

Acoustic Stimulation↗
PubMedDate not supplied

Frequency-specific information from click evoked otoacoustic emissions in noise-induced hearing loss.

Click evoked otoacoustic emissions (CEOAEs), pure-tone audiograms (PTAs), and Bekesy sweep frequency audiograms were recorded from 15 ears of 11 subjects with noise-induced hearing loss. For all ears, hearing threshold levels > or = 30 dB HL were found at the high frequencies. The aims of the study were to examine whether the decomposition of CEOAEs into narrow band components could identify hearing loss in a frequency-specific manner and to what extent audiometric thresholds could be predicted. CEOAEs were parcelled into 0.5-kHz-wide components by means of the wavelet transform. Reproducibility of CEOAE components was compared with audiometric threshold at corresponding frequencies. A general trend of low reproducibility for increasing audiometric thresholds was found. A reproducibility value of 60 per cent was found to best separate normal and elevated thresholds. The presence of a CEOAE component at a given frequency was always associated with audiometric thresholds < or = 20-25 dB HL. On the other hand, the absence of a component was equally associated either with normal or abnormal hearing levels. Large inter-subject variability was observed. A weak linear relationship was found between reproducibility and audiometric thresholds at corresponding frequencies, indicating that analysis of narrow band CEOAE components is valuable for separating normal from hearing-impaired ears but cannot replace the audiogram.

Acoustic Stimulation↗
PubMedDate not supplied

Temporal segmentation and multiple-source analysis of short-latency median nerve SEPs.

Short-latency (10-50 ms) median nerve somatosensory evoked potentials (SEPs) from four normal subjects were analysed by means of temporal segmentation techniques and source derivation methods. In each case the responses were recorded using 32 electrodes. Dipolar optimization was carried out with a time-varying technique, using three different approaches: regional source estimation, spherical source estimation (one radial and one tangential component), and multiple dipolar approach. This was to assess the relative influence on the dipolar solution of the different optimization techniques. The effect of the different number of channels in the estimation procedures has been also investigated. The methods of optimization are crucial, particularly for the orientation of P22. In all cases the source location estimated with the 32-electrode montage was shifted towards the centre of the spheres.

Computer Simulation↗
PubMedDate not supplied

'Derived nonlinear' versus 'linear' click-evoked otoacoustic emissions.

Recordings of emission evoked in response to transient stimuli (TEOAE) are partially contaminated by the initial stimulus artifact. For this reason, a nonlinear estimation method is widely used (derived nonlinear response, DNLR). The aims of this paper are: (1) to analyse some very basic properties of the derived nonlinear emissions such as the short-time input/output relationships; and (2) to show similarities and differences between the classical averaging (linear) and the derived nonlinear recording techniques, in the same ears, both in time and in the frequency domain. At latencies greater than about 6 ms, responses which are recorded using the derived nonlinear technique exhibit no additional features in comparison with linear recordings, at all stimulus levels. At latencies less than 6 ms, the derived nonlinear technique greatly reduces the linear content of the acoustic artifact, and the response may be considered as the initial part of the emission. However, the derived nonlinear responses tend to be considerably noisier than the linear emissions, thus reducing the effectiveness of the technique. The linear responses show a strikingly similar frequency content with respect to the derived nonlinear responses, at least at a high stimulus level and around the main peaks of the spectrum.

Acoustic Stimulation↗