Considerations on the Problem of Learning 143 



the life processes of the neurones. Only when over- 

 stimulated would we expect that there would be 

 any deleterious or annoying effects which are sup- 

 posed to result in the reduction of the permeability 

 of the synapse. Thorndike's doctrine then natu- 

 rally leads to the position that the vitally good 

 and pleasant stimulations are those of optimal or 

 sub-optimal intensity, while stimulations of greater 

 intensity would produce effects which are unpleas- 

 ant and deleterious, at least at the time. Are the 

 facts such as the theory would lead us to expect? 

 Stimulation of pain nerves produces sensations 

 which are generally disagreeable in all degrees of 

 intensity which can be appreciated. Shall we say 

 then that all stimulation of the neurones invqlved 

 in responses to pain giving stimuli are injurious to 

 the neurones involved? If so, practically all func- 

 tional stimulation of these neurones would be dele- 

 terious to them. On the other hand, certain sen- 

 sory systems may be stimulated strongly for a long 

 time without producing results that are unpleas- 

 ant. It is far from proven that the sensations 

 aroused by stimulating the nerves of touch, heat, 

 and certain of the nerves of taste and smell are ever 

 disagreeable, however strongly the end organs are 

 stimulated. It is probable that most of the unpleas- 

 ant results alleged to follow from overstimulating 

 a particular sense organ arise from the fact that 

 pain nerves become involved when the stimulating 

 agent is sufficiently strong. This is very probable 



