Page:Mind (New Series) Volume 12.djvu/495

PHYSIOLOGICAL FACTORS OF THE ATTENTION-PROCESS. 481 spectator of the series of changes ; ' Holding B ' means that I attempted to favour the predominance of the blue square by a voluntary effort, that is when the blue predominated I concentrated my attention upon it and when orange pre- dominated, or the two were fused to a neutral tone, I made efforts to recall the blue square. N in the table stands for the periods of neutral or mixed colour, and the figure stand- ing after N is the sum of these periods expressed in seconds during one rotation of the drum. The figure standing before or B is the number of appearances of this colour during the rotation, and the figure standing after or B is the sum of the periods of those appearances expressed in seconds. The latter are the significant figures, the number of appear- ances being of little importance. These figures appear at first sight somewhat chaotic but on consideration of them the following points appear very distinctly under equally favourable conditions. tends to predominate over B, and this tendency is obscured in I. a and exaggerated in I. b, because the field of the normal right eye is favoured, as against the field of the atropinised left eye, presumably through a slight activity of the intrinsic muscles of the normal eye. II. a and III. b show that a voluntary effort to favour the predominance of one colour-field is very successful when that colour is presented to the normal eye, the gain being 15" in the case of B and 14" in the case of 0. II. b and III. a show that the sensation excited in the retino- cerebral tract of the atropinised eye can also be favoured by voluntary effort but to a less degree than that excited in the normal eye, the gain being 11" and 9" for B and re- spectively. IV. a and b show that the effect of convergence: is twofold ; firstly the neutral periods are much prolonged at the expense of the periods of predominance of the pure colours ; this effect must be ascribed to the activity of the extrinsic muscles of both eyes which, maintaining the con- vergence of both eyes, re-enforces or supports the excitement of both cerebro-retinal tracts. Secondly, the field of the normal eye is favoured relatively to that of the atropinised eye and to a greater extent than when the visual axes are parallel ; this must be due to the increased activity of the intrinsic muscles of the normal eye that accompanies con- vergence. I will quote briefly the similar results of one other series of observations made by a different method. This series too was one of several made by the same method and giving similar results. A plate of milk-glass, 3 cm. square, let into window-shutter 31