674 



PHYSIOLOGY OF THE CEREBRUM 



The following table will give us some idea of the reaction time for the 

 different senses: 



For the sense of taste v. Vintschgau has found the following reaction 

 times for common salt, sugar and quinin : tip of the tongue, 0.597, 0.752 and 

 0.993 second respectively; for the base of the tongue, 0.543, 0.552 and 0.502 

 second respectively. The reaction time for different odors (oil of peppermint, 

 oil of rose and bergamot oil) varies in Moldenhauer's findings between 0.199 

 and 0.374 second. 



It is not surprising that the reaction times found by the different authors 

 for a given sense differ considerably, for the nervous organization of the sub- 

 ject has always to be taken into account. 



In most cases it requires some time for odoriferous and sapient substances 

 to come in contact with the appropriate nerve endings ; hence the longer time 

 consumed by a reaction to these stimuli than to others. 



The differences observed between the reaction times for sight, hearing and 

 touch are, as Wundt remarks, probably dependent upon the different intensities 

 of these stimuli. For one and the same sense the reaction time is always 

 shorter the stronger the stimulus. We cannot ordinarily compare the intensity 

 of a certain auditory stimulus with that of a certain visual stimulus, for there 

 is no standard of measurement common to the two. The threshold stimuli 

 for the different senses, however, being in all cases just sufficient to produce 

 an effect, must be relatively of the same strength. Wundt found in fact that 

 the reaction times for the visual, auditory and tactile stimuli in the neighbor- 

 hood of their threshold values were almost exactly equal, namely 0.331, 0.337, 

 and 0.327 second respectively. We infer from this and the facts summarized 

 in the table that auditory stimuli in general are more powerful than optical 

 or cutaneous stimuli. 



The reaction time is increased as the body or mind becomes fatigued, also 

 as the result of all sorts of exciting influences, but is reduced by practice, in 

 some cases very considerably. All this goes to prove that the length of the 

 reaction time depends essentially on the duration of the psychophysical process, 

 or in other words, that we dare not look upon the psychophysical process as a 

 perfectly constant factor. 



If warning be given of the signal just before it is made, the reaction time 

 is considerably shorter than otherwise. The subject has his whole attention 

 fixed on the coming event, and, by sufficient practice, he can make the central 

 connection so tense as to give the response almost as promptly as if it were a 



