Influence Of Stimulus Intensity Research Articles

Neuromagnetic evidence of an amplitopic organization of the human auditory cortex

It is well known that the location of the source of cortical auditory evoked responses, which can be determined neuromagnetically in humans using the concept of an equivalent current dipole (ECD), shifts with changing stimulus frequency (‘tonotopic organization’). Not investigated so far, however, is the question of whether there exists also an ‘amplitopic organization’ of the human auditory cortex, i.e., a spatial distribution of neurons maximally responsive to respective ‘best stimulus intensities.’ We measured, in the study presented here, in 3 normally hearing subjects the auditory evoked magnetic field (AEF) in response to tone-burst stimulation with a carrier frequency of 1000 Hz at 6 different intensities (30–80 dB HL in 10 dB steps). The influence of stimulus intensity was quantified in terms of changes in the ECD parameters (amplitude, direction and spatial coordinates) which were determined such that a maximum correspondence between observed and calculated field distributions was obtained. The results of the neuromagnetic measurements presented here prove that the ECD location also shifts with changing stimulus intensity. The depth of wave M100 (latency of about 100 msec) decreases monotonically with increasing stimulus intensity while the horizontal ECD position is slightly shifted in the anterior direction. The results imply that, while topical mechanisms of frequency coding are similar at cortex and at the cochlear level, topical mechanisms of intensity coding are different at these levels.

Influence of stimulus intensity on AEP components in the 80- to 200-millisecond latency range.

The influence of the intensity of passively perceived 1-kHz tones on the latencies and amplitudes of AEP components in the 80- to 200-ms latency range recorded from frontal, central and temporal electrode locations was investigated in healthy adult subjects. At stimulus intensities from 30 to 70 dB SL the latencies of the frontally and centrally recorded N100 and P175 waves decreased, their amplitudes increased. At stimulus intensities from 70 to 90 dB the latencies of N100 and P175 increased, N100 amplitude declined and P175 amplitude increased at a slower rate than between 30 and 70 dB. The latency of the N140 wave recorded at temporal electrode locations decreased markedly with increasing stimulus intensity.

Influence of stimulus intensity on the categories of single-unit responses recorded from olfactory bulb neurons in awake freely-breathing rabbits

This study analyzes the influence of increasing odor intensity on the single-unit activity of olfactory bulb neurons recorded in awake freely-breathing rabbits. Five odorants were delivered at four concentrations over a range of 2 log units. Inspiration-and expiration-related firing activities were analyzed separately to categorize the odor-evoked responses into excitation, suppression and no response. Increasing the odor concentration caused more neurons to show excitatory responses during the inspiratory phase of the respiratory cycle and/or suppressive responses during the expiratory phase. The highest concentration of each odor also caused several units to give suppressive responses during inspiratory phases or excitatory responses during expiratory phases. However, increasing odor concentration caused few responses (less than 2%) to change from excitation to suppression or vice versa. How these results relate to those from studies performed in anaesthetized animals and the implications of the results for olfactory coding will be discussed.

The influence of stimulus intensity and motivational differences on learned helplessness deficits

Two experiments are reported which assess the moderating effects on learned helplessness deficits of individual differences in task-specific motivation and expectation of control. In Experiment 1 a neutral stimulus was used and in this case only high motivation subjects displayed helplessness deficits in response to noncontingency training. In addition, high motivation subjects demonstrated greater sensitivity to the noncontingency than did low motivation subjects. However, when an aversive stimulus was used in Experiment 2 the moderating effect of motivational differences was removed and this was accompanied by greater sensitivity to the noncontingency on the part of low motivation subjects. Indeed, the learned helplessness effect in Experiment 2 was more pronounced within the low motivation group. The theoretical significance of these findings is explored and directions for future research are suggested.

Influence of stimulus intensity on odour discrimination by olfactory bulb neurons as compared with receptor cells

Previously reported electrophysiological responses recorded from individual neurons in the olfactory bulb of frogs stimulated with odorous compounds were further analyzed using statistical methods. Five of the odorants were delivered at two concentrations. The pattern of discrimination among these odorants was investigated with the aid of the Pearson's correlation test and Benzecri's ‘analyse des correspondances’. Special attention was paid to the incidence of odour concentration on this discrimination pattern. The results were compared with those of a similar study performed on receptor cells in the same experimental conditions. The comparison indicated that the information processing in the olfactory bulb seems to improve discrimination between chemically different stimuli, especially those poorly discriminated by receptor cell responses, whereas it protects this discrimination against a massive influence of the intensity of the stimuli.

Fetal heart rate response to controlled sound stimuli during the third trimester of normal pregnancy.

Fetal heart rate (FHR) responses to controlled sound stimuli were compared in the 32nd, 35th and 39th week of pregnancy. Though a tendency to a greater FHR response to sound was found as gestation advanced, this increase would seem to be so small that it may be ignored in practice. The earlier demonstrated influence of stimulus intensity and prestimulus heart rate level on the FHR response to sound were confirmed.

Habituation des menschlichen Orbicularis oculi-Reflexes

The habituation of the electrically (stimulation of the supraorbital nerve) elicited orbicularis oculi reflex (OOR) was investigated in 51 healthy volunteers (average age: 39 years). Ten reflex responses were registered from the left and right side including eyes open, eyes closed, and during task performance. The stimulus frequency was 1/s. The data were transmitted to an LAB 8e computer and statistically treated. The influence of stimulus frequency on habituation was examined separately. The following parameters of habituation as devised by Thompson and Spencer were demonstrable: dishabituation, habituation of dishabituation, spontaneous recovery, and influence of stimulus intensity. The analysis of habituation during task performance with the Kruskal-Wallis test revealed a statistically significant decrease of habituation. The early reflex component (R1) amplitudes increased during the 1/s stimulation. This effect was also statistically significant. The increase in R1 amplitude during 1/s stimulation was interpreted as „facilitation”.

Das mesothorakale Tympanalorgan vonCorixa punctata Ill. (Heteroptera, Corixidae)

1. Action potentials of the mesothoracic tympanic organ's two receptor units (“Al” and “A2”) were recorded extracellularly. The impulse activity of both receptor units rises beyond “resting activity” when stimulated by airborne sound. 2. The time course of the excitation of both receptor units appears to be phasic-tonic (Fig. 4). 3. The influence of stimulus intensity and its time course on the excitation of both receptor units was studied (Figs. 5–8). 4. The threshold curves of the receptor units “Al” and “A2” for airborne sound were determined in the frequency range between 0.3 to 20 kHz. The two receptor units differ. Receptor unit “Al” shows a distinct threshold minimum, whereas the threshold curve of the less sensitive receptor units “A2” appears more flat (Fig. 9). 5. The threshold curves of the receptor units on the left body side differ from those on the right. The threshold minimum of unit “Al” left is absolutely lower than that of “Al” right and lies at higher frequencies (Fig. 10). 6. As observed under the light microscope, vibrations of the organ's base and bulb differ from one side of the body to the other (Fig. 11). 7. Removing the bulb influences the mode of oscillation of the base as well as the threshold curves of the receptor units. 8. A hypothesis is proposed regarding the function of integumentary structures on the membrane in stimulus transformation.

The influence of stimulus intensity on sensitization of the flexor reflex

The influence of stimulus intensity on sensitization of the flexor reflex

Cortical audiometry. The influence of stimulus intensity upon evoked auditory potential in the normal person and in cases of hearing loss with recruitment.

The author demonstrates how there is a direct and proportional relation between the intensity of the stimulus and the amplitude of the E.R.A., for people with normal hearing as well as for patients with transmission or reception hearing loss. However, when the stimuli are intense in people with normal hearing the amplitude of the E.R.A. diminishes, and in patients who suffer a hearing loss with recruitment, the E.R.A. reaches a greater amplitude than the intensity of the sonorous stimulus used.

On the Limitations of Cochlear-Microphonic Measurements

The interelectrode phase and the relative microphonic magnitude have been measured from electrodes placed in scalae vestibuli and tympani of the first three turns of the guinea pig cochlea. The relative phase difference between two electrodes in a given turn appears to be a sensitive indicator of the contributions to the recorded microphonics of local and remote potential generators. It is suggested that in the guinea pig, local responses can be measured up to 10 000 Hz in the first turn, up to 3000 Hz in the second turn, and only up to 500 Hz in the third turn. The results of interaction between local and remote activity, as manifested in amplitude and phase patterns of the microphonic, are demonstrated in detail and the influence of stimulus intensity is treated. Attention is called to some of the pitfalls that result from drawing inferences from data that are obtained in a frequency region where the response is dominated by remote components. Finally, for comparison, interelectrode phase data are given for the first turn of the cat's cochlea, and the problems of recording from the round-window region are considered for both cat and guinea pig.

The influence of intensity of visual stimuli on the psychological refractory phase

The paper describes some experiments designed to test the predictions of an intermittency hypothesis concerning the influence of stimulus intensity on the delay in reaction to the second of a pair of visual stimuli. No agreement has been found between the experimental data and the predictions. A variant of the intermittency hypothesis is proposed in which the central system is not assumed to handle information on an all-or-none basis, but rather on the basis of a reduces sensitivity to new information; the sensitivity is assumed to be minimal immediately after the passage of a stimulus and is gradually restored to its initial value. Some psychophysical and neurophysiological evidence is given.