These twelve instances occurred with two subjects, three (to left) occurring with K. and nine (three each right, up, down) occurring with H. The cause was the same in all twelve instances, both H. and K. reporting that (in these cases) they had great difficulty in obtaining a reasonably vivid and distinct image when directed to move the image in the direction in which the object had been moved.  The attempt to move the image resulted in a vague image spread continuously over the entire area that had been covered by the moving object, and the effort to obtain the image at the desired position only was serious and took an appreciably longer time than usual.  It is to be noted, also, that the time usually taken by H. is uniformly very much greater than the time taken by the other subjects.  Yet, even with these instances included, the average time of all movements of the image in the direction in which the object had been moved is less than the average time of the other movements, the former being 2.41 seconds, the latter, 2.59 seconds.

TABLE VIII.

MOVEMENTS OF A SINGLE IMAGE.

I., OBJECT PREVIOUSLY MOVED; II., OBJECT NOT MOVED.

Average Time Given in Seconds.

Subjects:          B.                    G.                H.
I         II        I         II        I      II
To right,  0.57      1.30      0.55      1.46      6.95      7.15
Return,         0.35      0.58      0.27      0.92      5.40      4.51
To left,   0.60      1.06      0.45      1.15      5.95      6.42
Return,         0.40      0.73      0.35      0.89      4.10      4.41
Up,        0.42      1.05      0.45      0.99      6.85      5.96
Return,         0.42      0.46      0.25      0.76      5.30      4.36
Down,      0.57      1.10      0.47      0.82      8.77      5.85
Return,         0.42      0.45      0.27      0.06      5.55      4.40
General    0.54      1.13      0.48      1.10      7.13      6.34
Averages,       0.40      0.55      0.28      0.66      5.09      4.42

Subjects:          I.                    K.
I         II        I         II
To right,  2.05      1.28      2.35      4.80
Return,         1.15      0.67      1.17      2.40
To left,   1.30      1.34      2.57      4.63
Retur,          1.22      0.62      1.60      2.73
Up,        1.85      1.62      1.42      3.29
Return,         0.87      0.86      1.27      1.90
Down,      1.80      1.36      2.30      3.27
Return,         1.42      0.72      1.25      1.56
General    1.75      1.40      2.16      4.00
Averages,       1.16       0.72     1.32      2.15

If the record of H. is omitted from Table VII., a, c, and d, and that of K. from VII., b (as these are the records of the twelve exceptions), the former average becomes 1.44 seconds, the latter 1.86 seconds.

The following table affords the means of comparing the time taken in moving the image in the direction in which the object had been moved with the time taken in moving the image in the same direction when there had been no movement of the object.  The averages are obtained from the records of Tables VII. and I.