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the external skin and of the immediately adjoining parts of the mucous membrane, which
is not sensitive at once to stimulations of pressure, hot, cold, and pain. The degree of
sensitivity may, indeed, vary at different points, in such a way that the points most
sensitive to pressure, to hot, and to cold, do not, in generally, coincide. Sensitivity to pain
is everywhere about the same, varying at most in such a way that in some places the pain-
stimulus acts on the surface, and in others not until it has penetrated deeper. On the other
hand, certain approximately punctiform cutaneous regions appear to be most favorable
for stimulations of pressure, hot, and cold. These points are called respectively, pressure-
spots, hot-spots, and cold-spots. They are distributed in different parts of the skin in
varying numbers. Spots of different modality never coincide; still, temperature-spots
always receive sensations of pressure and pain as well; and a pointed hot stimulus applied
to a cold spot, always causes a sensation of hot, while hot-spots do not seem to be
stimulated by pointed cold stimuli. Furthermore, hot-spots and cold-spots react with their
adequate sensations to properly applied mechanical and electrical stimuli.
8. Of the four qualities mentioned sensations of pressure and pain form closed systems
which show no relations either to each other or to the two systems of temperature-
sensations. These last two, on the other hand, stand in the relation of opposites; we
apprehend hot and cold not merely as different, but as contrasted sensations. It is,
however, very probable that this is not due to the original nature of the sensations, [p. 48]
but partly to the conditions of their rise, and partly to the accompanying feelings. For,
while the other qualities may be united without limitation to form mixed sensations -- as,
for example, pressure and hot, pressure and pain, cold and pain - hot and cold exclude
each other because, under the conditions of their rise, the only possibilities for a given
cutaneous region are a sensation of hot or one of cold, or else an absence of both. When
one of these sensations passes continuously into the other, the change regularly takes
place in such a way that either the sensation of hot gradually disappears and a continually
increasing sensation of cold arises, or vice versa the sensation of cold disappears and that
of hot gradually arises. Then, too, elementary feelings of opposite character are
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OUTLINES OF PSYCHOLOGY
33
connected with hot and cold, the point where both sensations are absent corresponding to
their indifferent zone.
In still another respect the two systems of temperature-sensations are peculiar. They are
to a great extent dependent on the varying conditions under which the stimuli act upon
the sense-organ. A considerable increase above the temperature of the skin is perceived
as hot, while a considerable decrease below the same is perceived as cold, but the
temperature of the skin itself, which is the indifference zone between the two, can adapt
itself rapidly to the existing, external temperature within fairly wide limits. The fact that
in this respect too, both systems are alike, favors the view that they are interconnected
and also antagonistic.
B. SENSATIONS OF SOUND.
9. We possess two independent systems of simple auditory sensations, which are
generally, however, connected as a result of the mixture of the two kinds of impressions.
They are [p. 49] the homogeneous system of simple noise-sensations and the complex
system of simple tone-sensations.
Simple noise-sensations can be produced only under conditions that exclude the
simultaneous rise of tonal sensations, as when air-vibrations are produced whose rate is
either too rapid or too slow for tone-sensations to arise, or when the sound-waves act
upon the ear for too short a period. Simple sensations of noise, thus produced, may vary
in intensity and duration, but apart from these differences they are qualitatively alike. It is
possible that small qualitative differences also exist among them, due to the conditions of
their rise, but such differences are too small to be marked by distinguishing names. The
noises commonly so called are compound ideas made up of such simple noise-sensations
and of a great many irregular tonal sensations (cf. § 9, 7). The homogeneous system of
simple noise-sensations is probably the first to develop. The auditory vesicles of the
lower animals, with their simple otoliths, could hardly produce anything but these. In the
case of man and the higher animals it may be surmised that the structures found in the
vestibule of the labyrinth receive only homogeneous stimulations, corresponding to
simple sensations of noise. Finally, experiments with animals deprived of their labyrinths,
make it probable that even direct stimulations of the auditory nerve can produce such
sensations (p. 41). In the embryonic development of the higher animals, the cochlea
develops from an original, vestibular vesicle, which corresponds exactly to a primitive [ Pobierz całość w formacie PDF ]