THE FEELING OF EFFORT. H 



If in case 2, we think our eyes moving when they are in reality still, we shall judge 

 that we are following a moving object when we are but fixating a steadfast one. Illu- 

 sions of this kind occur after sudden and complete paralysis of special eye muscles, and 

 the partizans of feelings of efferent innervation regard them as experimenta crucis. 

 Helmholtz writes •} " When the external rectus muscle of the right eye, or its nerve, is 

 paralyzed, the eye can no longer be rotated to the right side. So long as the patient 

 turns it only to the nasal side it makes regular movements, and he perceives correctly 

 the position of objects in the visual field. So soon, however, as he tries to rotate it out- 

 wardly, i. e., towards the right, it ceases to obey his will, stands motionless in the middle 

 of its course, and the objects appear flying to the right, although position of eye and 

 retinal image are unaltered.^ 



" In such a case the exertion of the will is followed neither by actual movement 

 of the eye, nor by contraction of the muscle in question, nor even by increased tension 

 in it. The act of will produced absolutely no effects beyond the nervous system, 

 and yet we judge of the direction of the line of vision as if the will had exercised 

 its normal effects. We believe it to have moved to the right, and since the retinal 

 image is unchanged, we attribute to the object the same movement we have erroneously 

 ascribed to the eye. * * * These phenomena leave no room for doubt 



that we only, judge the direction of the line of sight by the effort of will with which 

 we strive to change the position of our eyes. There are also certain weak feelings 

 in our eyelids, * * * * g^^^j furthermore in excessive lateral 



rotations we feel a fatiguing strain in the muscles. But all these feelings are too 

 faint and vague to be of use in the perception of direction. We feel then what impulse 

 of the will, and how strong a one, we apply to turn our eye into a given position." 



Partial paralysis of the same muscle, paresis, as it has been called, seems to point 

 even more conclusively to the same inference, that the will to innervate is felt 

 independently of all its afferent results. I will quote the account given by a very recent 

 authority,^ of the effects of this accident : 



" When the nerve going to an eye muscle, e. g., the external rectus of one side, falls 

 into a state of paresis, the first result is that the same volitional stimulus, which under 

 normal circumstances would have perhaps rotated the eye to its extreme position 

 outwards, now is competent to effect only a moderate outward rotation, say of 20°. 

 If now, shutting the sound eye, the patient looks at an object situated just so far 

 outwards from the paretic eye that this latter must turn 20°, in order to see it 

 distinctly, the patient will feel as if he had moved it not only 20° towards the side, 

 but into its extreme lateral position, for the impulse of innervation requisite for brmging 

 it into view is a perfectly conscious act, whilst the diminished state of contraction 

 of the paretic muscle hes for the present out of the ken of consciousness. The test 

 proposed by von Graefe, of localization by the sense of touch, serves to render evident 

 the error which the patient now makes. If we direct him to touch rapidly the 

 object looked at, with the fore finger of the hand of the same side, the line through 



1 PhysioloTische Optik, p. 600. ever, learns to see correctly before many days or weeks are 



2 The left and sound eye is here supposed covered. If over. • • 

 both eyes look at the same field there are double images 's Alfred Graefe, in Handbucb der gesammten Augenheil- 

 which still more perplex the judgment. The patient, how- kunde, Bd. vi, S. 18. 



