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stimuli. For the psychological attributes of a sensation, however, this circumstance is
entirely irrelevant, and therefore such a definition of the term is unjustifiable. [p. 37] The
discrimination between sensational and affective elements in any concrete case is very
much facilitated by the existence of indifference-zones in the feelings. Then again, from
the fact that feelings range between opposites rather than mere differences, it follows that
they are much the more variable elements of our immediate experience. This changeable
character, which renders it almost impossible to hold an affective state constant in quality
and intensity, is the cause of the great difficulties that stand in the way of the exact
investigation of feelings.
Sensations are present in all immediate experiences, but feelings may disappear in certain
special cases, because of their oscillation through an indifference-zone. Obviously, then,
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OUTLINES OF PSYCHOLOGY
27
we call, in the case of sensations, abstract from the accompanying feelings, but never vice
versa. In this way two false views may easily arise, either that sensations are the causes
of feelings, or that feelings are a particular species of sensations. The first of these
opinions is false because affective elements can never be derived from sensations as such,
but only from the attitude of the subject, so that under different subjective conditions the
same sensation may be accompanied by different feelings. The second is untenable
because the two classes of elements are distinguished, on the one hand by the immediate
relation of sensations to objects and of feelings to the subject, and on the other by the fact
that the former range between maximal differences, the latter between maximal
opposites. Because of the objective and subjective factors belonging to all psychical
experience, sensations and feelings are to be looked upon as real and equally essential,
though everywhere interrelated, elements of psychical phenomena. In this interrelation
the sensational elements appear as the more constant; they alone can be isolated through
abstraction, by referring them to external objects. It follows, therefore, of necessity that in
investigating the attributes of both, we must start with the sensations. Simple sensations,
in the consideration of which we abstract from the accompanying affective elements, are
called pure sensations. Obviously, we can never speak of "pure feelings" in a similar
sense, since simple feelings can never be thought of apart from the accompanying
sensations and combinations of sensations. This fact is directly connected with the second
distinguishing characteristic mentioned above (p. 34 sq).
§ 6. PURE SENSATIONS
1. The concept "pure sensation" as shown in § 5 is the product of a twofold abstraction:
1) from the ideas in which the sensation appears, and 2) from the simple feelings with
which it is united. We find that pure sensations, defined in this way, form a number of
disparate systems of quality; each of these systems, such as that of sensations of pressure,
of tone, or of light, is either a homogeneous or a complex continuity (§ 5, 5) from which
no transition to any other system can be found.
2. The rise of sensations, as physiology teaches us, is regularly dependent on certain
physical processes that have their origin partly in the external world surrounding us,
partly in certain bodily organs. We designate these processes with a name borrowed from
physiology as sense-stimuli or sensation-stimuli. If the stimulus is a process in the outer
world we call it physical; if it is a process in our own body we call it physiological.
Physiological stimuli may be divided, in turn, into peripheral and central, according as
they are processes in the various bodily organs outside of the brain, or processes in the
brain itself. In many cases a sensation is attended by all three forms of stimuli. Thus, to
illustrate, an external impression of light acts as a physical, stimulus on the eye; in the
eye and optic nerve there arises a peripheral physiological stimulation; finally a central
physiological stimulation takes place in the corpora quadrigemina and in the occipital
regions of the cerebral cortex, where the optic nerve terminates. In many cases the
physical stimulus may be wanting, while both forms of physiological stimuli are present;
as, when we perceive a flash of light in consequence of a violent ocular movement. In
still other cases the central stimulus alone is present; as, when we recall a light [p.39]
impression previously experienced. The central stimulus is, accordingly, the only one that
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OUTLINES OF PSYCHOLOGY
28
always accompanies sensation. When a peripheral stimulus causes a sensation, it must be
connected with a central stimulus, and a physical must be connected with both a
peripheral and a central stimulus.
3. The physiological study of development renders it probable that the differentiation of
the various sensational systems has been effected in part in the course of general
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