12 WILLIAM JAMES ON 



which the finger moves -will not be the line of sight directed 20" outward, but will 

 approach more nearly to the extreme possible outward line of vision."' 



A stone cutter with the external rectus of the left eye paralysed, will strike his hand 

 instead of his chisel with his hammer, until experience has taught him wisdom. 



It appears as if here the judgment of direction cov,ld only arise from the excessive 

 innervation of the rectus when the object is looked at. All the afferent feelings must be 

 identical with those experienced when the eye is sound, and the judgment is correct. 

 The eye ball is rotated just 20° in the one case as in the other, the image foils on the same 

 part of the retina, the pressures on the eyeball and the tensions of the skin and conjunc- 

 tiva are identical. There is only one feeling which can vary, and lead us to our mistake. 

 That feelino" must be the effort which the will makes, moderate in the one case, excessive 

 in the other, but in both cases an efferent feeling, pure and simple. 



Beautiful and clear as this reasoning seems to be, it. is based on an incomplete invent- 

 ory of the afferent data. The writers have all omitted to consider what is going on in 

 the other eye. This is kept covered during the experiments to prevent double images, 

 and other complications. But if its condition under these circumstances be examined, it 

 will be found to present changes which must result in strong afferent feelings. And the 

 taking account of these feelings demolishes in an instant all the conclusions which the 

 authors from whom I have quoted, base upon their supjoosed absence. This I will now 

 proceed to show. 



Take first the case of complete paralysis and assinne the right eye affected. Suppose 

 the patient desires to rotate his gaze to an object situated in the extreme right of the 

 field of vision. As Bering has so beautifully shown, both eyes move by a common act of 

 innervation, and in this instance both move towards the right. But the paralyzed right 

 eye stops short in the middle of its course, the object still appearing far to the right of 

 its fixation point. The left sound eye, meanwhile, although covered, continues its rotation 

 until the extreme ritrhtwai'd limit tliereof has .been reached. To an observer lookino; at both 

 eyes the left will seem to squint. Of course this continued and extreme rotation pro- 

 duces afferent feelings of rightward motion in the eyeball, which momentarily overpower 

 the faint feelings of centi-al position in the diseased and uncovered eye. The j^atient feels by 

 his left eye-ball as if he were following an object which by his right retina he perceives 

 he does not overtake. All the conditions of optical vertigo are here present : the unage 

 stationary on the retina, and the erroneous conviction that the eyes are moving. 



The objection that a feeling in the right eyeball ought not to produce a conviction that 

 the left eye moves, will be considered in a moment. Let us meanwhile, turn to the case 

 of simple paresis with apparent translocation of the field. 



Here the right eye succeeds in fixating the object, but observation of the left eye will 

 reveal to an observer the fact that it squints just as violently inwards as in the former 

 case. The direction which the finger of the patient takes in pointing to the object, is 

 the direction of this squinting and covered left eye. As Graefe says (although he fails to 

 seize the true import of his own observation), " It appears to have been by no means suffi- 

 ciently noticed how significantly the direction of the line of sight of the secondarily 

 deviating eye, [i.e., of the left,] and the line of direction of the pointed finger agree." 



1 Ib'id, p. 21. 



