Abstract
(1) Electromyographic (EMG) responses induced by short bursts of white noise have been studied in 8 human subjects. The stimuli were either of a fixed intensity with the intervals varying randomly, or at fixed intervals with 3 different intensities in random succession. Each subject was submitted to several sequences of about 30 min each, consisting of a series of 50 to 150 stimuli. (2) EMG responses consisted of ‘early’ and ‘late’ components which can be considered as the EMG manifestation of the startle response and the orienting response, respectively. (3) The amplitude of the startle reaction shows a clear positive correlation with the intensity of the stimulus; no such correlation was found for the oreinting reaction. (4) A significant correlation seems to exist between the amplitude of the startle reaction and the ‘frequency’ of the EEG measured during the 1 sec period just preceding the tone stimulus. (5) The amplitude of the orienting reaction displays a fair correlation with that of the startle; however each component may be present at times independently of the other. (6) During some sequences of stimuli, it has been possible to observe a habituation of both the startle and the orienting responses. However the occurrence of habituation seems to be strongly correlated with the variability of the EEG recorded during the sequence: that is, habituation can be observed if the distribution of EEG ‘frequencies’ displays a small dispersion around its modal value. (7) It is suggested that startle and orienting reactions, while corresponding to 2 different psychomotor activities, may be engendered by a common neuronal structure, probably located in the bulbar reticular formation. (8) The results obtained would favor the hypothesis that habituation of the motor responses may be the manifestation of a decrementing process occurring principally in the lower nervous centers, including spinal neurons, implicated in the observed responses. Modulating influences, coming from higher structures, may interfere with this process by introducing superimposed ‘noise’.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
