Boris Sidis,
The Foundations of Normal and Abnormal Psychology…
(1914
| notes)
“ The same holds true of a whole psycho-physiological system,―there is a threshold of sensitivity below which the minimal stimulus cannot fall, the latter does not awaken any reaction in the system. All the senses reveal the presence of such thresholds which are also present in the case of all the higher psycho-physiological systems. If we term the stimulus which can just bring about a reaction in the system the stimulus threshold, we can say that a given system can only be thrown into activity by a stimulus rising in intensity above the stimulus threshold. ”
