Page:Mind (New Series) Volume 8.djvu/46

 32 MAEGAEET FLOY WASHBUEN : dark lines lasting some time and growing lighter, inter- rupted once by a momentary green image. The lines then became bright, and the red negative image remained until the end of the series, traces of blue appearing from time to time. After the usual interval, the subject was asked to turn the image green in the next experiment, and the follow- ing colour sequence was obtained : A light green image with dark lines, the lines gradually becoming reddish ; then a red image with green lines, the lines spreading till the whole image was dark green, which it remained until its entire disappearance. Finally, where blue was visualised, the sequence of colours was : purple positive, light blue positive, light blue positive with greenish lines, very short red negative, vivid blue negative with yellow lines. Such results as these show that for a person with un- usually vivid powers of visual imagination, central excita- tion of visual centres, whose peripheral excitation by white light is so far weakened that the corresponding colour sensa- tions have quite disappeared from the after-image, may re- inforce their activity to such an extent as to make their sensations predominate in the image. We have here an extreme case of the effect of central reinforcement on weak peripheral excitation ; an effect which appears to a less marked degree in the results from the other subjects. The most obvious theoretical consideration suggested by these phenomena is one which hardly needs to be dwelt on, since it has been recognised for so long and is supported by so many other lines of evidence. I mean the fact that perception and idea differ ultimately only in the manner of their production. The after-image, while of peripheral origin, stands in point of intensity midway between the two. Here, where the intensity of the peripheral process is reduced to a minimum, the resulting conscious state is seen to be practically identical in character with that pro- duced by central excitation. But the chief interest of these experiments is their bearing on the theory of attention. The writer can state from her own introspection that for the three subjects of moderate visualising powers the effort to call up subjectively a certain colour meant simply an unusually intense effort to attend to that colour. That is, the central excitation of the visual centre was of the same order as that which occurs when one prepares to attend to certain conscious contents, e.g., a certain overtone in a clang. Now if these experiments show anything, they show that the function of attention is positive as well as nega- tive, intensifying as well as inhibiting; and further that