Amplitude Change Rate Research Articles

Speech Analysis Techniques for Detecting Stress

While attempts to assess the level of stress present in an individual by analyzing his speech have shown some success, current methodology is best described as being capable of determining whether a talker is presently experiencing either minimum or maximum stress. For example, Jones (1990) found that, for those extremes of stress, both the increase in speaking fundamental frequency and the decrease in vocal jitter were statistically significant. Neither measure, however, was capable of distinguishing any intervening levels. Researchers continue searching for acoustic measures that might more precisely indicate ongoing changes in stress to establish a metric capable of more than simply differentiating between the two extremes. The objective is to distinguish among several levels of stress or to furnish a continuous, concurrent estimate of the talker's state. Two main components are considered for improving the estimation of a talker's actual stress level: 1) refinements in the acquisition of signals and their processing; and 2) proposals concerning the choice of acoustic parameters. The first objective is intended to maintain signal fidelity which should enhance the potential to detect changes in the speaker's voice. For acquisition of the acoustic signal, direct sampling and storing to a computer is highly recommended, thus eliminating the potential distortion that is inherent in tape recording. During the analog-to-digital conversion phase, the highest sample rates attainable in the face of storage limitations and the finer amplitude resolution provided by 16 bit converters should also be beneficial. Concerning the selection of acoustic parameters, in addition to speaking fundamental frequency and jitter, certain variations in the waveform (spectrum) might be exploited. The maximum rate of change in amplitude during a pitch period or the ratio of the energy in various segments of the spectrum, after each has been appropriately normalized, might not only indicate stress levels but also be independent of speaker variability.

閃光刺激下における脳幹網様体興奮性に及ぼす外来刺激の影響(II)

As a part of the study to elucidate the influence of exteroceptive stimulation on the excitability of the brainstem reticular formation in the presence of flash stimuli, the effect on the recruiting response was investigated in the rabbit and the following observed.1) The amplitude of the recruiting response appearing in the cerebral cortex EEG increased, on stimulation of the nucleus centrum medianum, nucleus reticularis and nucleus ventralis anterior (VA), belonging to the diffuse thalamocortical projection system, by 8Hz when the soft contact lens (CL) or the hard CL was attached in the absence of the flash stimulus.2) The amplitude of this recruiting response was suppressed and decreased when the soft CL or hard CL was attached in the presence of the flash stimulus.3) The amplitude of this recruiting response increas ed when tlhe flash stimulus was given. This finding indicates that the suppression of the recruiting response by the flash stimulus when the CL is attached is not due to the flash stimulus alone.4) The rate of change in the amplitude of the re cruiting response with of the soft CL and the hard CL was analyzed quantitatively by determination of the wave pattern using the digital computor (Nihon Kohden ATAC-201). In the absence of the flash stimulus, an increase in amplitude of the recruiting response of an average of +23% (soft CL) and +45% (hard CL)respectively while in the presence of the flash stimulus, there was an average decrease of 15% (soft CL) and 18% (hard CL), respectively. The rate of change in amplitude with the flash stimulus alone averaged +18%. These results sugget that t he previously reported decrease in excitability of the brainstem reticular formation on attachment of the CL in the absence of the flash stimulus and the increase in the presence of the flash stimulus can be attributed to a rise in indirect suppression (in the absence of the flash stimulus) and a decrease in indirect suppression (in the presence of the flash stimulus) via the diffuse thalamocortical projection system.

Modification of plasma solitons by resonant particles

A consistent theory of plasma soliton interaction with resonant particles is developed. A simple derivation of a perturbed Korteweg–de Vries equation with the interaction term is presented. It is shown how the known limit cases (such as Ott–Sudan’s, etc.) can be derived from the general equations and what their regions of applicability are. Some effects caused by the soliton-particle interaction (amplitude change-rate, tail formation, etc.) are analyzed by means of a recently developed perturbation method. The analytical results are compared with a direct numerical integration of the perturbed Korteweg–de Vries equation. Laboratory measurements carried out in a strongly magnetized, plasma-filled waveguide and results from particle simulation are interpreted in terms of the analytical results.

ON AN IMPULSE INTERVAL GENERATING MECHANISM.

1. Some of the data obtained by HAGIWARA (1954) on the interval fluctuations of the sensory nerve impulse have been reanalysed with a modified model.2. The modification consisted essentially of the introduction of a factor characterizing the rate of fluctuation of a random process that is thought to be super-imposed on the threshold of the impulse triggering mechanism.3. The mean rate of change in amplitude of the step-wise defined random process was found to be in the order of a few hundred per second.4. Some of the implications of the model: the time course of the random function immediately after an impulse, the large value of the noise intensity relative to the rheobase and, as a consequence, the predicted existence of spontaneous discharge, were discussed.