856 OF SENSATION, AND THE ORGANS OP THE SENSES. 



occupied, even without a distinct effort of the will, by those received through 

 another. If we look at a sheet of white paper through two differently-colored 

 glasses at the same time one being placed before each eye the resulting 

 sensation is seldom that of a mixture of the colors : if the experiment be tried 

 with blue and yellow glasses, for example, we do not see the paper of a uni- 

 form green ; but the blue is predominant at one moment, and the yellow at 

 another ; or blue nebulous spots may present themselves on a yellow field, or 

 yellow spots on a blue field. We perceive, from this experiment, that the 

 attention may not only be directed to the impressions made on either retina, to 

 the complete exclusion of those of the other, but it may be directed to those 

 made on particular spots of either. This may be noticed, again, in the process 

 by which we make ourselves acquainted with a landscape or a picture ; if our 

 attention be directed to the whole field of vision at once, we see nothing dis- 

 tinctly ; and it is only by abstracting ourselves from the contemplation of the 

 greater part of it, and by directing our attention to smaller portions in succes- 

 sion that we can obtain a definite conception of the details. The same is the 

 case in regard to auditory impressions ; and here the power of attention, in 

 causing one sensation or series of sensations to predominate over others which 

 are really more intense, is often most remarkably manifested. When we are 

 listening to a piece of music played by a large orchestra, for example, we may 

 either attend to the combined effect of all the instruments, or we may single 

 out any one part in the harmony, and follow this through all its mazes ; and a 

 person with a practised ear (as it is commonly but erroneously termed, it being 

 not the ear, but the mind, that is practised), can even distinguish the sound of 

 the weakest instrument in the whole band, and can follow its strain through the 

 whole performance. This attention to a single element can only be given, 

 however, by withdrawing the mind from the perception of the remainder ; and 

 a musician who thus listens, will have very little idea of the rest of the har- 

 monic parts, or of the general effect. In fact, when the mind is thus directed, 

 by a strong effort of the will, into a particular channel, it may be almost con- 

 sidered as unconscious quoad any other impressions. 



862. The effects of attention are not only manifested in regard to the sensa- 

 tions which are excited by external impressions, but also in respect to those 

 which originate within the system. Every one is aware how difficult it is to 

 keep the body perfectly quiescent, 1 especially when there is a particular motive 

 for doing so, and when the attention is strongly directed to the object. This is 

 experienced even whilst a photogenic likeness is being taken, when the position 

 is chosen by the individual, and a support is adapted to assist him in retaining 

 it ; and it is still more strongly felt by the performers in the " tableau vivans," 

 who cannot keep up the effort for more than three or four minutes. Now it is 

 well known that, when the attention is strongly directed to an entirely different 

 object (when we are listening, for example, to an eloquent sermon, or an inte- 

 resting lecture), the body may remain perfectly motionless for a much longer 

 period ; the uneasy sensations, which would otherwise have induced the indi- 

 vidual to change his position, not being perceived : but no sooner is the dis- 

 course ended, than a simultaneous movement of the whole audience takes place, 

 every one then becoming conscious of some discomfort, which he seeks to re- 

 lieve. This is the case also in regard to the respiratory sensation ; for it may 

 generally be observed that the usual reflex movements do not suffice for the 

 perfect aeration of the blood, and that a more prolonged inspiration, prompted 

 by an uneasy feeling, takes place at intervals; but under such circumstances as 

 those just alluded to, this feeling is not experienced until the attention ceases to 

 be engaged by a more powerful stimulus, and then it manifests itself by the 



1 Of course the movements of respiration and winking are left out of the question. 



