CHAPTER XLV 



MEMORY 



Memory an after-effect of stimulus Persistence dependent on strength of stimulus 

 Rate of forgetting Multiple after-effects in retina Spontaneous revival of 

 after-images Theories of memory Latent images and their revival After- 

 effect of stimulus on excitability and conductivity Differential effect of diffuse 

 stimulus Revival of latent image in metal Revival of latent image on phos- 

 phorescent surface Negative or reversed memory-image Psycho-physio- 

 logical version of this experiment Differential excitation under diffuse 

 stimulus, internal or external Continuity of this seen in mechanical response 

 of plagiotropic stem and pulvinus of Mimosa, in the electrical discharge of 

 certain fishes, and in psychic response of memory. 



UP to the present we have considered only the immediate 

 effects of stimulus. We know, however, that excitation 

 entails, not only an immediate, but also an after-effect. We 

 are thus led to the question of the physical aspects of the 

 phenomenon known as memory, which is admittedly a 

 matter of after-effects. Even with the somewhat insensitive 

 apparatus for the detection of nervous changes which is at 

 our disposal the galvanometer or the Kunchangraph we 

 find that the after-effect of strong is more persistent than 

 that of feeble stimulus. In the very sensitive neurile 

 apparatus, nervous changes and their after-effects are more 

 distinctly perceived. The psychological retention of an 

 impression follows, in general, the curve of response and 

 recovery. The fact that physiological recovery from the effect 

 of strong stimulus is less rapid than from feeble, has its 

 correspondence in the period required for the fading of 

 sensory impressions, of which also it may be said that the 

 stronger persist longer than the weak. 



This fact that the after-effect of strong stimulus persists 



