506 Transac tions . — Miscellaneous . 



Art. LXXIII. — After-images. 

 By Miss K. Browning. 



[Read before the Hawke's Bay Philosophical Institute, 21st July, 1892.] 



The phenomena to which I wish to draw your attention 

 to-night are so common that my only excuses in bringing 

 them before your notice are — firstly, the great interest I have 

 always taken in the subject ; and, secondly, the hope that if, 

 after hearing the notes, you say to yourselves, " We knew 

 all that before," some other member will take up the theme 

 and tell us a little about his experiences, or throw some further 

 light on the question. 



Every one has noticed after-images, but few realise what 

 an important bearing they have on the discussion of memory, 

 for, unless percepts persisted for a time, we should be unable 

 to grasp the idea that separate perceptions — say a, b, c, cl, e — 

 form one whole. After-images form a connecting-link between 

 percepts and revived mental images, and they probably under- 

 lie many of the lesser acts of remembering, as Sully has well 

 pointed out. Revived mental images are more important, 

 because they lead to greater knowledge ; but a clear under- 

 standing of after-images forms a good introduction to the 

 subject of reproductive imagination. 



It will be well at the beginning of this paper to define 

 clearly what is meant by an image in psychology. James 

 Sully, in his Outlines, distinguishes an " image " from a 

 " percept " by saying that a " percept " is largely presentative, 

 while an " image " is representative. 



On the other hand, considering "images" under the head- 

 ing of "ideas," an "image" differs from a "concept" or 

 " general notion," for the latter deals with a class, while the 

 former represents a concrete object or mental picture. 



But the after-images I wish to speak of to-night are 

 physiological rather than psychological phenomena ; and it 

 would have been better to have called them "after-percepts" 

 had not the name "after-image" been better known. After- 

 percepts of sight are the most frequent, although I have heard 

 or read of after-percepts derived from all the organs of sense 

 and movement. But to-night I shall deal only with the 

 images of the organs of sight. 



These images are divided into two classes — positive and 

 negative. By a positive image we mean that colours in the 

 representative image are of the same kind as in the presented 

 object, while in a negative after-image the light colours become 



