Tables II. and III. show the results of experiments in changing the color of a single image. This was usually a square, sometimes a disc. The time of optical perception was five seconds. After the disappearance of after-images, if there were any, eighteen to twenty-four changes were made in the color of the memory image, occupying from four and a half to six minutes. The colors were saturated blue, green, yellow and red, and each one was changed into each of the other colors and then restored. The order of change was varied to avoid uniformity of succession. The four colors were shown to the subjects each day before the experiments began, to establish a standard. The time was taken with a stop-watch, and includes the time between the director's word of command, 'green,' etc., and the subject's report, 'now,' or 'green,' etc. It includes, therefore, two reaction times. The subject reported 'now' the instant he secured the desired color, not waiting for the completion of the shape that usually followed. TABLE II. CHANGES OF COLOR. SINGLE IMAGE. 72 CHANGES OF EACH COLOR. [Label 1: Subject.] [Label 2: To Green.] [Label 3: Return to Blue.] [Label 4: To Yellow.] [Label 5: Return to Blue.] [Label 6: To Red.] [Label 7: Return to Blue.] [Label 8: To Blue.] [Label 9: Return to Green.] [Label 10: To Yellow.] [Label 11: Return to Green.] [Label 12: To Red] [Label 13: Return to Green.] From Blue. From Green. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] B. 1.72 0.50 1.66 0.38 1.81 0.50 1.23 0.56 1.10 0.65 1.33 0.56 G. 1.15 0.60 1.10 0.79 0.89 0.65 1.75 0.87 1.04 0.75 1.35 0.71 H. 4.67 4.25 4.87 4.06 4.81 3.83 5.27 4.50 5.81 4.89 5.37 4.94 I. 2.27 1.25 1.77 1.19 1.83 1.25 2.15 0.93 1.71 1.04 1.92 1.15 J. 1.38 0.81 1.29 0.94 1.29 0.95 1.65 1.08 1.15 0.77 1.60 0.81 K. 2.35 1.71 1.96 1.66 2.10 1.19 2.25 1.25 2.17 1.73 2.44 1.27 Av. 2.26 1.52 2.11 1.50 2.15 1.39 2.41 1.53 2.15 1.65 2.34 1.57 [Label 1: Subject.] [Label 2: To Blue.] [Label 3: Return to Yellow.] [Label 4: To Green.] [Label 5: Return to Yellow.] [Label 6: To Red.] [Label 7: Return to Yellow.] [Label 8: To Blue.] [Label 9: Return to Red.] [Label 10: To Green.] [Label 11: Return to Red.] [Label 12: To Yellow.] [Label 13: Return to Red.] From Yellow. From Red. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] B. 1.79 1.06 1.35 0.87 1.89 1.10 1.54 0.58 1.71 0.62 1.31 0.71 G. 1.50 1.10 1.48 0.87 1.31 0.88 1.33 0.92 1.35 0.91 0.77 0.58 H. 5.02 4.54 5.73 3.91 6.15 4.17 6.35 3.91 5.89 4.69 5.54 4.37 I. 2.29 1.31 2.54 1.19 2.29 1.27 2.85 1.10 2.50 1.21 1.65 1.31 J. 1.35 0.98 1.35 0.65 1.27 0.88 1.42 1.04 1.31 1.02 1.25 0.85 K. 3.02 1.52 3.21 2.04 2.23 1.79 2.54 1.56 2.66 1.60 2.88 1.81 Av. 2.49 1.76 2.61 1.59 2.52 1.68 2.67 1.51 2.57 1.68 2.23 1.62