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rise from 2 to 3 the other must rise from 100 to 1,000, and so
forth. Fechner himself allowed that this rule holds good only
for stimuli of a medium strength. There is a definite limit to

1 Ricliet, Recherches siir la SensibilUe, p. 170, seq.

- Helmholtz, Physioloirische Optik,\s. 161 ; Henle, Ueher den Geschmackssinn ("On
the Sense of Taste ") {AnthropoL yortrage, n.), \i. iS. [Bernstein, Five Sittset 0/ Man,
p. 80, seq. (Tr.)]



v] THE PSVCIIOLOGV OF COGNITIOX in

the sensibility of the visual organ, and if two stimuli of unequal
strength both exceed this limit, the difference between them cannot,
from the nature of the case, be apprehended.

The lower limit to the rule is conditioned by the fact, that,
when the stimuli are very weak, the internal condition of the
organ and of the nervous system comes appreciably into play.
In respect of the eye, the so-called " natural light," which
arises without any external influence, effects a sort of "normal
hallucination." 1 The other senses also seem to be never wholly
free from subjective sensations, which become of much im-
portance only when external stimuli are very weak. \'ery weak
stimuli are, moreover, incapable of overcoming the resistance
offered by the retina." But even with regard to stimuli of medium
strength, the universality of the rule has been brought into
question ; it appears to have undisputed approximate validity
only for medium stimuli in the provinces of the visual and muscular
senses, and perhaps of the sense of hearing. The question which
still awaits a satisfactory answer is, whether special reasons can
be shown for the exceptions to the rule which occur in several
of the sense-provinces.

But whether a mathematical formula can be successfully
applied or not, all experience points to the fact that the rise
and prominence of sensations are determined by their reciprocal
relation. Every sensation, as it emerges, has to undergo a struggle
with other possibilities of sensation, and it depends on the result
of this struggle whether the sensation comes at all into con-
sciousness and with what degree of clearness and definileness.
The several members in the series of sensations are not therefore
absolutely independent of one another. This is ground where
it is difficult to find the right expressions. For if it is said that
sensations fuse through rapid succession, or where the difference
in strength is too small or too great, it may be objected that
under these circumstances sensations do not separately arise at all,

1 "The black tliat we see in the dark and when our eyes are shut, is a sensation of
light which we have without external stimulus, not to be confounded with the seeing
nothing which we have in the finger or at the back of the head, and not to be compared
to the hearing nothing when there is no external sound. The black which we see when
our eyes are closed, is only the same sensation of light which we have when we
look at a black surface, and which may go through all gradations up to the strongest
sensation of light ; indeed the internal black in the eye itself is sometimes changed by
purely internal causes into clear light, and is sprinkled, so to speak, with luminous
phenomena. On closer attention, we discover in the black of the clo-sed eye a sort of fine
light-dust, the abundance of which varies in different persons and different conditions of
the eye, and which in pathological states may amount to brilliant appearances of light."
G. Th. Kechner, EUmente Jer Psycho-phyiik., i, p. 165, scq.

* E. Kraepelin in W'undt's StiiiiUn, ii., p. 3.^4.



112 OUTLINES OF PSYCHOLOGY [v

and that consequently they cannot be said to fuse. We stand
here at the very threshold of consciousness, where the psychical
elements approach unconsciousness, and where, consequently,
psychological terms can be only half figuratively employed. The
general psychological bearing of the phenomena seems, however,
clear enough ; there is no series of absolutely independent sensations,
but every sensatio7i is determined by its relation to the one experienced
immediately be/ore it or at the same time.

4. A 'corresponding rule is found to hold for the quality of
sensations.

The same excitation may, under different circumstances, produce
the sensation now of warmth, now of cold. If, e.g., the hand
is placed in a vessel of the same temperature as the room,
a temperature to which it is accustomed, warmth is felt, because
the radiation of heat from the hand is prevented in the smaller
space. If one vessel is filled with water of the temperature cor-
responding to that of the hand, a second with water of a higher,
and a third with water of a lower temperature, and if the right
hand is dipped in the second and the left hand in the third vessel,
and then both together in the first vessel, the right hand will feel
cold and the left hand warm in this first vessel where previously
neither would have felt cold or warmth.

The same movement is felt either as exertion or as rest, ac-
cording as it succeeds a slower or a more violent movement. The
sense of rest, indeed, only properly arises through contrast to the
sense of change or motion. Sudden cessation of a stimulus may
give rise to a very lively sensation, as when an unexpected pause
in a loud piece of music startles the audience, or when the miller
is awakened by the stopping of the mill. The same surface appears
rough or smooth according to the character of the preceding or
accompanying sensations of touch. The taste of wine is brought
out by eating cheese ; after bitter or salt tastes water seems sweet.

This effect of contrast, through which the special quality of sen-
sation is seen to be subject to conditions similar to those that
determine the rise of sensation in general, is especially conspicuous
in the province of visual sensations.

To see only one single colour would be the same as seeing no
colour at all. If several very small coloured objects are placed side
by side, their colour quality may often be apprehended, although
that of one of them, at the same visual angle, cannot be recognised.'

1 Hermann's Handbuch, iii., p. 199.



V] rilK PSYCHOLOGY OF COGNITION 113

The deepest black is apprehended only by the side of the purest
white, and in contrast to it. The different colour qualities come
out most strongly (are most deeply " saturated ") when accom-
panied by their complementary colours. Colours are called com-
plementary when their combined rays produce the sensation of
grey or white. The complementary colours are : —

Red .... Bluish green.

Orange .... Azure blue.

Yellow .... Indigo blue (ultramarine blue).

Green .... Purple.

Violet .... Yellowish green.

If one colour is placed by the side of another which is not its
complementary colour, the one will always be affected by the
complementary colour of the other. A grey strip on a coloured
ground receives a tinge of the colour complementary to the ground,
and if a grey strip is laid upon a succession of differently coloured
pieces of paper, it acquires a different tinge on each piece of paper.
In making this experiment, we must place a piece of thin transparent
paper over the grey strip ; for if there is a distinct outline between
the strip and the ground, the tinge does not appear.^

Contrast may be not only simultaneous but also successive. A
colour will appear " saturated," not only when seen by the side of
its complementary colour, but also when it immediately follows it.
If the eye is allowed to dwell for some time on a certain colour, it
becomes the more disposed to a strong sensation of the comple-
mentary colour. And if the eye is transferred from a colour to a
white or grey ground, it sees in the latter a tinge of the comple-
mentary colour ; thus a reddish gleam is seen on a white wall, if a
green curtain has been previously gazed at. The most distinctly
marked sensation of a colour arises through the combination of
simultaneous and successive contrast.

Without being noticed, similar effects of contrast enter into all
our sensations of colour. We seldom look long at cme point, for it
requires a certain effort to fix the gaze for even a short time, and
after-images from the one point of the visual orbit influence in
consequence the apprehension of other points. The most com-
plicated combinations of simultaneous and successive contrasts are
often produced.

1 [C/ Kenistein, p. i6i. (I'rJJ



114 OUTLINES OF PSYCHOLOGY [v

The effect of contrast does not rest upon erroneous inference
or upon illusion. Such an explanation would be possible only if the
effect of contrast were confined to exceptional cases. But it is
always experienced in a greater or less degree, at any rate in the
province of sight, and it is consequently impossible to point out
a normal sensation. What is the ground on which a colour must
be seen for its true quality to be recognized ? In practice, of
course, a normal or typical shade is taken as the true colour ; but
in reality every determination of quality is relative. In its quality,
as in its existence, every sensation is determined through its
relation to other sensations.^

5. The study of sensations thus corroborates the general account
of consciousness given in an earlier chapter (II. 5). It is impos-
sible to resolve consciousness into a series of simple and self-
existent sensations, absolutely independent of one another. A
sensation which stands in no relation to any other is not known
to us. This law may be called the lai.u of relativity^- From
the inotnent of its first coming into being, the existence and
properties of a sensatiofi are determined by its relation to other
sensations.

The law of relativity accords with the principal law of the
physiology of the nervous system, that no constant state, but only a
change effected with a certain suddenness, calls to life a nerve-
process. The preceding state of the organism and of conscious-
ness thus forms a background to the succeeding state. Effect of
contrast in its narrow sense is only a specially striking example of
what in some measure takes place, and must take place, in every
sensation. It is so easily overlooked only when the degree of
contrast is small, or when two sensations are at such a distance
from one another that they are not thought of in conjunction;
the intermediate links are then forgotten. The clearly defined
and distinct sensations are built up out of a host of slightly differing
sensations.

The distinction or the relation may be either simultaneous or
successive. The successive relation is, however, the most primitive.
Simultaneous sensations have a tendency to fuse (especially in

1 In the opinion of some, qualities of sound form an exception, no effect of contrast
taking jilace in these. Ouliers maintain that a tone sounds differently, according as it is
taken in the ascending or descending scale. — If the exception is more than apparent, the
inquiry must be made whether it may not be founded on special conditions of the sense
cf hearing.

'•i This term was, so far as I know, first introduced by Wundt. [For its several appli-
cations , >,ee r.ncy. Brit., Art. " Psychology " (under Theory of Presentation). (Tr.)]



V] THE PSYCHOLOGY OF COGNITION 115

the departments of touch, taste and smell) ; and since, on the
other hand, the attention is no more quiescent than is the bodily eye,
but wanders from point to point, even a complex stimulus is from
the nature of the case apprehended as successive. Moreover,
successive apprehension is clearer than simultaneous. Small dis-
tinctions of weight are more easily perceived by weighing
successively with the same hand than by weighing simultaneously
with both hands ; the temperature of two liquids is compared
better by putting the same hand successively into both, than by
putting either hand simultaneously into one of the liquids. Very
faint shadows are noticed only when the object which casts the
light is moved. Infants and the lower animals appear to have far
smaller power of distinguishing between simultaneous, than be-
tween successive stimuli. This accords with^the general law of
relativity and with the fundamental law of the physiology of the
nervous system ; for excitations at rest do not occasion anything like
the same change and the same contrast as excitations which succeed
one another. Successive contrast takes effect more forcibly than
contrast between things given together.^

As already observed, no distinction can be drawn between
absolute and relative sensation, or between sensations and dif-
ferences of sensation. This consequence of the psychology and
physiology of sensation is, however, still disputed even by such a
writer as Fechner, who has done so much to show the importance
of the law of relativity. "It is true," he says,-' "that, since we
never have sensations of a certain kind or strength without preceding
or accompanying sensations of a different kind or strength, no strict
experimental proof can be adduced of the possibility of having
sensation which is not so preceded or accompanied ; but I tind
neither theoretical nor experiential grounds to forbid the sup-
position, and accordingly believe — nor can the contrary view be
based on more than a belief— that, if a child were to awake for the
first time in an absolutely uniform bright light, all other stimuli
being so far as possible removed (though it is true they could not
be completely removed), he would still see the brightness of the
light." Fechner recognized correctly that it is necessary to go

1 E. H. Weber, Tastsir.n unJ Ctiiteingcfuhl i^'' ?i<tx\<,t of Touch and Common Sensa-
tion") (Wagner's Physiot. I/aniixtuh-terl'iich, iii., 2), p. 544; Fechner, EUiiienle dcr
/'svchophysik, i., p. 174; <"■. H. Schneider, " Waruni bemerken wir massig bewegle
Gegenstiinde leichter als ruhende?" (''Why do we observe objects moving at a moderate
rate more readily than objects at re-^t'i") (l'ic:rti-//a/irssc/ir./Hr U'/ssi'nsc/t. J'/u'/os., ii.)
p. 411.

- \ii S\i,:/ien ifer Psj\/iop/iyi:i, II. 114.



ii6 OUTLINES OF PSYCHOLOGY [v

back to the first sensation, that is, to the beginning of conscious-
ness, if the law of relativity is to be escaped. His example, how-
ever, affords no absolute beginning ; for the child awaking to the
brightness of the light, would have had general and motor, and
perhaps other sensations, before he received the sensation of light ;
this latter sensation would therefore have those indefinite sensations
as a background, and consequently would make its appearance
with a character different from all later sensations of light. Per-
haps preparations might even ha\e been made for it by internally
aroused processes in the visual organ, in consequence of which the
threshold would have been already crossed. Moreover, the light-
stimulus (even if in itself absolutely uniform) does not produce
precisely the same eftect in two successive moments ; in the first
moment there is a vague apprehension and excitement which only
gradually gives way to sight proper ; and in this transition the law
of relativity takes effect, for the state in each moment is determined
by that which preceded it. This at least is certain, that the more
nearly a mental state approaches to absolute unity, or rather sim-
plicity, the closer is the approach to the confines of consciousness.
{Cf. IL 5.) It cannot therefore be supposed that all shades of
difference and all rhythm can disappear while consciousness still
exists.^

If the law of relativity has complete validity, no sharp line can
be drawn between sensation and thought. In the way in which, in
successive relativity {e.g. in the effect of successive contrast), the
preceding determines the succeeding sensation, an elementary
memory is apparent. The influence of distance in time, of op-
position and contrast, shows us sensation as a discrimination, an
apprehension of differences, an elementary comparison. Here

' Stumpf (^Tonfisychologie, i., p. 10) objected to this {a/>ro/>os of my article "Ziir
Psychologic der (lefiihle" ("On the Psychology of the Keeiings") in the '^ J'hiloso-
pliisclifn Monatshcften" 1880, in which the above line of thought had already appeared),
that just as certainly as the conscious life of the individual must have had a beginning,
there must have been a first sensation ; and since this could not stand in relation to any
other sensation, he regarded the law of relativity as condemned. — It is not, however, so
certain that there must have been one first sensation. It is also conceivable (ty. III.
6 and 9) that several sensations, mutually conditioning one another, should emerge
together ; and this is, in fact, the most probable view, for every organism, at every
instant, is subject to various different external influences, while, in addition, the internal
states of the organism act more or less upon the brain. — Stumpf does not take into
account the fact that, from conscious life as we know it and are able psychologically to
study it, we cannot make in the slightest degree intelligible a first simple sensation of this
kind. If conscious life begins with a single first sensation, then it begins with a condition
to which we have no parallel. (Cf. also II. 5.) Noteworthy in the extreme is the
conclusion which .Stumpf draws from the necessity of a single first sensation: "The
universality and necessity of relativity in the emergence of sensations, is to be regarded
m>,rely as a something acquired, as a ' second nature,' like every strong habit." If
the peculiar property of our conscious life, expressed in iht law of relativity, is a habit,



V] THE PSYCHOLOGY OF COGNITION 117

therefore is the very simplest form of the same conscious activity,
which at higher stages of development makes its appearance as
thought proper. And, finally, it is clear that the interaction among
sensations, which conditions their rise and their quality, is possible
only because" all sensations are members of one and the same con-
sciousness, which embraces and unites them. No contrast is
possible between my sensation of red and another person's
sensation of bluish green. Even if we conceive consciousness as
a series of sensations, synthesis is still therefore a necessar>' pre-
supposition.

A main point in the philosophy of Kant is corrected by these
results. Kant distinguished sharply between the matter and the
form of our knowledge. Sensations he regarded as a passively re-
ceived matter, which is arranged by a formative activity, derived
from a source wholly different from sensations. These latter, the
material of knowledge, are, according to Kant, given, while the
forms in which the material is arranged and worked up, are d
priori, that is to say, lie in the nature of our consciousness. Kant's
argument is that " that in which alone sensations can be arranged
and put in a certain form cannot itself be sensation." According to
the law of relativity, however, sensations form and determine one
another uninterruptedly, and no absolutely unformed matter is to be
found in consciousness; such matter would involve the possibility of
pure, absolutely independent sensations. The difference between
matter and form is only one of degree. Psychological experience
affords only approximations to purely passive sensations— and even
these are approximations to the confines of consciousness.^

6. Even if the sensations are regarded as only given or received,
it must be observed that they are not all derived from the external
world. For in the first place the organism is itself a little world,

then it is a habit which is acquired very early (immediately after the first sensation), and
a "second nature" that appears so early might well be placed in the rank of a "first
nature." As is seen, Stumpf does not really reject the law of relativity, although he
denies that it states an original property of conscious life. He tries to draw a distinction
between the sensation itself, and its discrimination. But every proper discrimination
pre-supposcs the interaction of the sensations tlicmselves, which is the earliest form of the
conscious activity, called at a higher stage comparison and judgment. Language has
provided no perfectly adequate expression for a relation so elementary as this. _ _

1 This was clearly seen by Salomon Maimon, one of the most penetrating disciples
of Kant. "Sensation," he says, "is a modification of the cognitive faculty, realized
in it only through endurance (without spont;ineity) ; but it is a mere idea to which
we may approach through tlie lowering of lonscioiisness, but which we can never
really reach." I'ersiuh iiber die Transi:endentalphilosof hie d'^V.^.iVj on the Transcen-
dental Philosophy"), lierlin 1790, p. 168. Maimon is, however, inconsistent inhis ritilo-
sophischen IVffrterbtuh ("Dictionary") (1791), when he defines "sensibility as "the
capacity of perceiving sensuous ciualitics in themselves, apart from all conntction and
relation pf one I o another."— V. 14.



n8 OUTLINES OF PSYCHOLOGY [v

confronting the greater world with a certain independence. Its
own internal activities yield important impressions (general
sensations). Nutrition, the circulation of the blood and respiration
pursue their course independently, to a certain extent, of what
passes without ; and these internal processes excite stronger or
weaker sensations. In the second place, the organism does not
wait for the external world to bring stimuli to it, but executes
movements which are accompanied by sensations : motor-scnsaiions.
Even before sensations arise through excitations from the external
world, movements, as some hold,^ are executed in consequence of
the superabundance of potential energy in the nerve-centres. These
movements, from a psychological point of view spontaneous and
unmotived, can occasion motor-sensations, which are probably
among the very earliest sensations of dawning consciousness.

The change or transition, which every conscious act presupposes,
or in w'hich it consists, may thus be as well active as passive in
character. Excitations not only come to us from without, but also
pass out from us. And the active changes may even perhaps
precede the passive, since conscious life first finds expression in
spontaneous, reflective and instinctive movements {cf. IV. 4 — 6).

From the psychological standpoint, motor-sensations may be
divided into two groups ; into sensation of effort and muscular
sensation. Sensation of effort is the sensation of the energy
exerted in carrying out a certain movement. We adjust and
measure, voluntarily or involuntarily, the degree of effort required
for a certain movement, and, before the actual movement, can have
a pre-experience of the energy as thus called up. Similarly, with-
out actually attempting a movement, we can feel our powerlessness
and exhaustion. Muscular sensation is a sensation of the
temporary state of one or more muscles. It may come from
muscles which are not under the control of higher nerve-centres
(as the sensation of cramp in the leg, colic, labour-throes), but may
also result from the state into which the muscle is put by motor-
impulses from the brain (sensation of muscular tension, or of
fatigue).

On the other hand, it is still uncertain whether these two classes
of sensations are equally distinct as regards their corresponding phy-
siological processes. It is held by some that the motor-process set
up in the motor-centres of the brain, before leaving the brain, sends
through nerve-fibres an excitation from the motor to the sensory

i [Bain, Mental Science, p. xt,seq. (Tr.)]



V] THE PSYCHOLOGY OF COGNITION iic

centres. This would give a class of sensations dvie to excitations
originating in the brain itself. These have been called sensations
of innervation. This view was held by J oh. Miillcr,' who relied
chiefly on the argument that, before an actual movement, before
raising a weight or mounting a flight of steps, we can feel
the degree of effort about to be made. Others explain all
motor-sensations, sensation of effort as well as actual muscular
sensation, as due to excitations sent from the muscle to the brain,
which thus receives as it were notice of the commencing or com-
pleted contraction of the muscle. That we feel or calculate in
advance the force to be applied, is, then, to be explained by the
effect of experience and habit. If this latter view is correct, and
it has been much strengthened by Sachs' discovery of sensory
nerves passing from the inside of the muscle to the higher centres,^
then in the sensation of effort wc experience not the actual com-



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