Dec. 23, 1869] 
NATURE 
213 
SENSATION AND PERCEPTION.—I. 
\ ees different meanings have been attached to the 
words sensation and perception by different writers ; 
and this diversity of meaning is to be met with in 
physiological as well as in more strictly philosophical 
works. Yet it is most important that we should come to 
a definite understanding upon the subject, in order to 
know whether certain physiologists have been warranted 
in assigning sensation and perception to different parts of 
the brain, as functions of separate portions of this principal 
organ of mind. 
The distinct issue raised is, Are physiologists justified in 
assuming that the so-called sensory ganglia, at the base 
of the brain, are the centres in which mere unconscious 
herve impressions are converted into conscious sensations? 
are these ganglia, in fact, in any sense, seats of Con- 
sciousness ? 
Almost everyone understands that both sensation and 
perception, however they may be supposed to differ from 
cne another, are nevertheless conscious states, or modes 
of consciousness in the special and ordinary acceptation 
of the term. But there is one distinguished writer, at 
least, who has most strenuously objected to this limita- 
tion, in the case of the word sensation. Mr. G. H. Lewes 
maintains* that what most other people term mere im- 
pressions or unconscious nerve actions, should really be 
regarded as sensations, and should be entitled also to 
the attribute of consciousness—not in its more special 
acceptation, but in accordance with the very general 
meaning which he attaches to this word. For the sensa- 
tions and perceptions of other writers—those impressions to 
which our attention is given—he reserves the single term 
perception, apparently because he considers there is no 
fundamental distinction between them. With this latter 
part of his doctrine, as will be seen, we are disposed 
thoroughly to agree, though we cannot assent to the pro- 
priety of so far revolutionising the meanings of the words 
sensation and consciousness. The fundamental position 
which Mr. Lewes assumes, and upon the strength of which 
he considers it desirable to make such an innovation in 
the meanings of thoroughly accepted terms is :—“ that 
sensibility is the property inherent in gangliontc tissue— 
the one peculiar ‘force’ belonging to all nerve centres, as 
neurility belongs to all nerves.”+ Now Mr. Lewes himself 
points out, that the only means of upsetting his argument 
(which must be otherwise logically irrefutable) is to deny 
that sensibility is a property of ganglionic tissue, and to 
look upon it as a _/w#ctzon rather of certain nerve centres. 
‘And this really seems to us to be the conclusion most 
strongly supported by obtainable evidence. Instead of 
Lclieving sensibility to bethe property inherent in ganglionic 
Ussue, should we not rather assign to this some more 
general characteristic, such as molecular instability, 
conferring upon it a property of mere 7#presszbzlity— of 
which sensibility and consciousness are the most special- 
ised modes, dependent upon the organisation and mole- 
cular instability of certain nerve centres of the cerebral 
lemispheres? Mr. Herbert Spencert calls a ganglion 
ccll a “ébero-motor element ; because in the most general 
conception of its property it seems to be a portion of 
cxtremely unstable matter, in which the molecular move- 
ments imparted to it by the afferent nerve-fibre undergo a 
prodigious multiplication before producing their ulterior 
cfrects. 
Just as we meet with this notable exception to the gene- 
rally received meaning of the word sensation, so also has 
ihe word perception been endowed with an altogether 
special meaning, by that school of philosophers known as 
Natural Realists: some of them have removed it also 
from the sphere of consciousness as ordinarily, under- 
stood. Space will not permit of my showing how they 
differ amongst themselves in minor shades of meaning : 
* “Physiology of Common Life.” vol. ii. 1859. 
+ Loc. cit. p. 20. y System of Philosophy, No, 20, 1868. 
I will only now quote the views of Dugald Stewart. 
He says:*—“In order to form an accurate notion 
of the means by which we acquire our knowledge of 
things external, it is necessary to attend to the dis- 
tinct meanings of the words sexsation and perception. 
The former expresses merely that change tn the state of the 
mind which is produced by an impression upon an organ 
of sense (of which change we can conceive the mind to 
be conscious without any knowledge of external objects) ; 
the latter expresses the /vow/edge we obtain by means 
of our sensations of the qualities of matter.” This is an 
explanation of perception which to most physiologists 
would appear absolutely meaningless. It seems itself 
utterly incomprehensible. Stewart conceived perception to 
be a distinct mental act by which we obtain a “know- 
ledge” of the properties of matter as existing, and in 
themselves. But, strange to say, this “knowledge” we 
“obtain by means of our sensations ;” even though by the 
word sensation Stewart understood “ merely that change in 
the state of the mind which is produced by an impression 
upon an organ of sense.” How, through such changes in 
the state of the mind, we are to arrive at an immediate 
knowledge of the things without which, ex hypothesz, the 
changes are not produced, we are at a loss to understand ; 
and neither do we see how it can be reconciled with 
Stewart’s own theories, seeing that, according to him, 
consciousness “ denotes the immediate knowledge which 
the mind has of its sensations and thoughts, and, in 
general, of all its present operations.” On the one hand, 
“knowledge” is made to transcend the sphere of con- 
sciousness ; whilst on the other, it is said that “of all the 
present operations of the mind, consciousness is an 
inseparable concomitant.” 
With these exceptions, the different acceptations of the 
words sensation and perception are less divergent, inas- 
much as nearly all other writers suppose consciousness, in 
the ordinary meaning of the word, to be an attribute of 
both states. And if they are both modes of consciousness, 
then the only further question to be considered is, whether 
there is any fundamental difference between them, such as 
would warrant physiologists in assuming the existence of 
an organic centre for the realisation of sensations, alto- 
gether distinct and apart from that whose functional 
activity gives rise to perceptions; or whether the two 
words are applicable only to the extremes of a series 
between whose terms there are the most innumerable and 
insensible gradations? If the latter view be the correct 
one, if the difference is one of degree rather than of kind, 
then we should be much more consistent in regarding 
sensations and perceptions as arising from the activity of 
one and the same organ ; and from a consideration of this 
question we may, therefore, derive some help towards the 
correct interpretation of the results of operations on the 
brains of certain lower animals, which have hitherto given 
rise to much discussion amongst physiologists. 
Professor Bain has well shown, in his “ Emotions and 
Will,” how sensation in its most strict aceeptation does 
insensibly merge into that which is more usually spoken 
of as perception. He shows that the more “sensation 
involves cognitive or intellectual processes, the more liable 
is it to fall under the title of perception.” “Some sensa- 
tions,” he says, “are mere pleasures and pains, and little 
else ; such are the feelings of organic life, and the sweet 
and bitter tastes and odours. Others stretch away into the 
region of pure intellect, and are nothing as respects en- 
joyment or suffering ; as, for example, a great number of 
those of the three higher senses.” But it seems to us 
that Mr. Bain stops short of the truth when he says,t 
“the lowest or most restricted form of sensation does not 
contain an element of knowledge.” It does not contain 
knowledge, it is true, in its highest sense, involving affir- 
mation and belief, but as a state of consciousness it is 
* Collected works of Dugald Stewart, edited by Hamilton, vol. ii. p. 14. 
¢ Loc. cit. p. 586 (Second Edition). 
