ish and obscure, because the parts of the retina receiving most light
get fatigued, and arouse no more sensation than those less fatigued
and stimulated by light from less illuminated objects. Or look
steadily at a black object, say a blot on a white page, for twenty
seconds, and then turn the eye on a white wall ; the latter will seem
dark gray, with a white patch on it ; an effect due to the greater
excitability of the retinal parts previously rested by the black, when
compared with the sensation aroused elsewhere by light from the
white wall acting on the previously stimulated parts of the visual
surface. All persons will recall many instances of such phenomena,
whicTi are especially noticeable soon after rising in the morning.
* Martin • op. cit.
6I0HT. 45
Similar things may be noticed with colors ; after looking at a red
patch the eye turned on a white wall sees a blue-green patch ; the
elements causing red sensations having been fatigued, the white
mixed light from the wall now excites on that region of the retina
only the other primary color sensations. The blending of colors so as
to secure their greatest effect depends on this fact ; red and green go
well together because each rests the parts of the visual apparatus
most excited by the other, and so each appears bright and vivid as the
eye wanders to and fro ; while red and orange together, each exciting
and exiiausting mainly the same visual elements, render dull, or in
popular j)hrase ' kill,' one another.
"If we fix steadily for thirty seconds a point between two white
s(juares about 4 mm. (^ inch) apart on a large black sheet, and then
close and cover our eyes, we get a negative after-image in which are
seen two dark squares on a brighter surface ; this surface is brighter
close around the negative after-image of each square, and brightest of
all between them. This luminous boundary is called the corotia, and
is explained usually as an effect of simultaneous contrast ; the dark
after-image of the square it is said makes us mentally err in judg-
ment, and think the clear surface close to it brighter than elsewhere ;
and it is brightest between the two dark squares, just as a middle-
sized man l>etween two tall ones looks shorter than if alongside one
only. If, however, the after-image be watched, it will often be
noticed not only that the light band between the squares is intensely
white, much more so than the normal idio-retinal light [see below],
but, as the image fades away, often the two dark after-images of
the squares disappear entirely with all of the corona, except that
part between them which is still seen as a bright band on a uniform
grayish field. Here there is no contrnst to produce the error of judg-
ment ; and from this and other experiments Hering concludes that
light acting on one part of the retina produces inverse changes in all
the rest, and that this plays an important part in producing the
phenomena of contrasts. Similar phenomena may be observed with
colored objects; in their negative after-images each tint is represented
by its complementary, as black is by white in colorless vision."*
Tlii.s i.s one of tlie facts referred to on p. 27 wliicli have
made Hering reject the psycliological e.xplanution of siniul-
taneou.s contra.st.
The Intensity of Luminous Objects. — Black is an optical
sensation. We have no black except in the field of vie^v ;
♦ Martin, pp. 525-8^
46 PSTCHOLOOT.
we do not, for instance, see black out of our stomach or out
of the palm of our hand. Pure black is, however, only an
* abstract idea,' for the retina itself (even in complete objec-
tive darkness) seems to be always the seat of internal
changes which give some luminous sensation. This is what
is meant by the ' idio-retinal light/ spoken of a few lines
f back. It plays its part in the determination of all after-
images with closed eyes. Any objective luminous stimulus,
to be perceived, must be strong enough to give a sensible
increment of sensation over and above the idio-r3tinal
light. As the objective stimulus increases the perception
is of an intenser luminosity; but the perception changes,
as we saw on p. 18, more slowly than the stimulus. The
latest numerical determinations, by Konig and Brodhun,
were applied to six different colors and ran from an in-
tensity arbitrarily called 1 to one which was 100,000 times
as great. From intensity 2000 to 20,000 Weber's law held
good; below and above this range discriminative sensibility
declined. The relative increment discriminated here was
the same for all colors of light, and lay (according to the
tables) between 1 and 2 per cent of the stimulus. Previous
observers have got different results.
A certain amount of luminous intensity must exist in an
object for its color to be discriminated at all. "In the
dark all cats are gray." But the colors rajaidly become
distincter as the light increases, first the blues and last the
reds and yellows, up to a certain point of intensity, when
they grow indistinct again through the fact that each takes
a turn towards white. At the highest bearable intensity of
the light all colors are lost in the blinding white dazzle.
This again is usually spoken of as a 'mixing' of the sensa-
tion white with the original color-sensation. It is no mix-
ing of two sensations, but the replacement of one sensation
by another, in consequence of a changed neural process.
CHAPTER IV.
HEARING.*
The Ear. — " The auditory organ in man consists of three
portions, known respectively as the external ear, the
middle ear or tympanum, and the internal ear or labij'
Fio. 17.— Semidiaprammatlc section through the rijfht ear (Czermak). M,
concha; (t. fxt«Tiial umliiory meatus; 7*. tympanic membrane; P, tympanic
cavity; «. oval foramen; r, rounil foramen; A', pliarynijeal openinp of Kiista-
chiiin tiil>e; 1'. vestibule; li, a semicirculur canal; i>', the cochlea; 17, scala
veHtitjuli; Pf, soala tympani; yl, auditory nerve.
rintJi ; the latter contains the end-organs of tlie auditory
nerve. The external car consists of the ex))ansion seen on
the exterior of the head, called the concha, M, Fig. 17,
• In tJ'arliitif^ the anatomy of the ear, great a.s.sis(ance will l)e
yielded by tlic admirable model made by Dr. Air/oiix, 5(5 \\\\y\ de
Vaii^(irard, Parin, described in the catalogue of the lirm aa "No. 21
— OreilU, tcmporrU de (M) cm., nouvelle edition," etc.
48
PSTCHOLOOY.
and a passage leading in from it, the external auditory
meatus, G. This passage is closed at its inner end by the
tympanic or drum membrane, T. It is lined by skin,
through which numerous small glands, secreting the wax
of the ear, open.
" Tlie Tympanum {P, Fig. 17) is an irregular cavity in
the temporal bone, closed externally by the drum mem-
brane. From its inner side the Eustachian tube (B) pro-
ceeds and opens into the pharynx. The inner wall of the
tympanum is bony except for two small apertures, the oval
and round foramens, o and r, which lead into the laby-
rinth. During life the round aperture is closed by the
Jining mucous membrane, and the oval by the stirrup-
bones. The tympanic vnembrane T, stretched across the
outer side of the tympanum, forms a shallow funnel with
its concavity outwards. It is pressed by the external air
on its exterior, and by air entering the tympanic cavity
through the Eustachian tube on its inner side. If the
tympanum were closed these pressures would not be always
equal when barometric pressure varied, and the membrane
would be bulged in or out according as the external or in-
ternal pressure on it were
the greater. On the other
hand, were the Eustachian
tube always open the sounds
of our own voices would
be loud and disconcerting,
so it is usually closed ; but
every time we swallow
it is opened, and thus the
air-pressure in the cavity
is kept equal to that in the
external auditory meatus.
Fig. 18 -Mcp, Mc, Ml and Mm stand for Qn makiuff a balloOU asceut
different paits ut the malleus; je, Jo, _ • ti
J/, J;W, for different parts of the incus or ffOlUg rapidlv d0W71 a
S IS the stapes. i • .i it i
deep mine, the sudden and
great change of aerial pressare outside frequently causes
}flT
HEARINO. 49
]minful tension of the drum-membrane, which may be
greatly alleviated by frequent swallowing.
The Auditory Ossicles. — Three small bones lie in the
tympanum forming a chain from the drum-membrane to
the oval foramen. The external bone is the malleus or
hammer ; the middle one, the incus or anvil ; and the in-
ternal one, the stapes or stirrup. They are represented in
Fi?. 18.*
Accommodation is provided for in the ear as well as in
the eye. One muscle an inch long, the tensor tympani,
i«.rises in the petrous portion of the temporal bone (running
in a canal parallel to the Eustachian tube) and is inserted
into the malleus below its head. When it contracts, it
makes the membrane of the tympanum more tense.
Another smaller muscle, the stapedius, goes to the head of
I be stirrup-bone. These muscles are by many persons felt
distinctly contracting when certain notes are heard, and
fome can make them contract at will. In spite of this,
uncertainty still reigns as to their exact use in hearing,
thougli it is highly probable that they give to the mem-
branes which they influence the degree of tension best
Baited to take up whatever rates of vibration may fall
upon them at the time. In listening, the head and ears in
lower animals, and the head alone in man, are turned so as
best to receive the sound. This also is a part of the reac-
tion called * adaptation ' of the organ (see the chapter on
Attention).
The Internal Ear. — " The labyrinth consists primarily of
chambers and tubes hollowed out in the temporal bone and
inclosed by it on all sides, except for the oval and round
foramens on its exterior, and certain apertures for blood-
vessels and the auditory nerve; during life all tliese are
closed water-tight in one way or another. Ikying in the
f>ony labyrinth thus constituted are membranous parts, of
the same general form but snudler, so that between th« two
•This description is ul)ri<I^M(l fmin Murtin'n ' Human Body'
50
PSTCHOLOOY.
a space is left; this is filled with a watery fluid, called the
ferilympli ; and the membranous internal ear is filled by
a similar liquid, the endolymph.
Fig. 19. — Casts of the bony labyrinth. A, left labyrinth seen from the outer
side; i?, right labyrinth from the inner side; C, left labyrinth from above; Co,
cochlea; V, vestibule; Fc. round foramen; Fv, oval foiamen; h. horizontal
semicircular canal; ha, its ampulla; vaa. ampulla of anterior vertical semi-
circular canal; vpa, ampulla of posterior vertical semicircular canal; vc, con-
joined portion of the two vertical canals.
The Bony Labyrinth. — " The bony labyrinth is described
in three portions, the vestibule, the semicircidar canals,
and the coclilea ; casts of its interior are represented from
different aspects in Fig. 19. The vestibule is the central
part and has on its exterior the oval foramen {Fv) into
which the base of the stirrup-bone fits. Behind the vesti-
bule are three bony semicircular canals, communicating
with the back of the vestibule at each end, and dilated near
one end to form an amjmlla. The bony cochlea is a tube
coiled on itself somewhat like a snail's shell, and lying in
front of the vestibule.
The Membranous Labyrinth. — "The membranous vesti-
bule, lying in the bony, consists of two sacs communicating
by a narrow aperture. The posterior is called the utri-
culus, and into it the membranous semicircular canals
open. The anterior, called the sacculus, communicates by
a tube with the membranous cochlea. The membranous
semicircular canals much resemble the bony, and each has
UKARINO.
01
an ampulla; in the ampulla one side of the membranous
tube is closely adherent
to its bony protector; at
this point nerves enter
the former. The rela-
tions of the membranous
to the bony cochlea are
more con;plioated. A
section thruugh this part
of the auditory appara-
tus (Fig. ~U) shows that
its osseous portion con- ^^^ ^ _^ ^^^^.^^ ^^^^^_^^ ^^^ ^^^^^^ .^
sistS of a tube wound two ihe line of its axis.
and a half times round a central bony axis, the modiolus.
From the axis a shelf, the lamina spiralis, projects and
partially subdivides the tube, extending farthest across in
its lower coils. Attached to the outer edge of this bony
plate is the membranous cochlea {scala media), a tube tri-
ano-ular in cross-section and attached by its base to the
outer side of the bony cochlear spiral. The spiral lamina
and the membranous cochlea thus subdivide the cavity of
the bony tube (Fig. 21) into an upper portion, the scala
Fio. 21.— Swtlon of OIK- (•■.11 of the ciM-hlcn, iimiriiiflcil. .ST, itrnin Vfstihiili ;
H. m»*inl>rane of K«-ihKiier; ('(', mfiiiliiiinous ci.t-hlru i.ini/M iiiritin); lln, thnhiia
Ittmimr. njuralis ; t, U-ctorial tiifiiiliruiic; ST, scala (yiiipani ; hu, Hplrul
lamina; rv>, ro<lH of C<»rti; b, basilar iiiiMiil)rHiie.
ve.stihrdi, SV, and a lower, the scala tympani, ST. Be-
tween these lie tlie lamina Kpinilis (/.so) and tlie mem-
52
P8TCH0L0Q1,
branous cochlea {CO), the latter being bounded above by
the membrane of Reissiier {R) and below by the basilar
membrane [h)." *
The membranous cochlea does not extend to the tip of
the bony cochlea; above its apex the scala vestibuli and
sciila tympani communicate. Both are filled with peri-
lymph, so that when the stapes is pushed into the oval
foramen, o, in Fig. 17, by the impact of an air-wave on
the tympanic membrane, a wave of perilymph runs up the
scaia vestibuli to the top, where it turns into the scala tym-
, pani. down whose whorls it runs and pushes out the round
foramen r, luffling probably the membrane of Reissner and
the basilar membrane on its way up and down.
The Terminal Organs. — "The membranous cochlea con-
tains certain solid structures seated on the basilar mem-
brane and forming the organ of Corti. This contains the
end-organs of the cochlear nerves. Lining the sulcus
A B
Fig. 22.— The rods of Corti. A, a pair of rods separated from the rest; B, a
bit of the basilar membrane with several rods on it, showing how they cover
in the tunnel of Curti ; i, inner, and e, outer rods; b, basilar membrane; r,
reticular membrane.
spiralis, a groove in the B^kgQ of the bony lamina spiralis,
are cuboidal cells ; on the inner margin of the basilar mem-
brane they become columnar, and then are succeeded by a
TOW which bear on their upper ends a set of short stiff
hairs, and constitute the inner Jiair-cells, which are fixed
below by a narrow apex to the basilar membrane; nerve*
fibres enter them. To the inner hair-cells succeed th^
* Ma.rtin • op. cU.
HEARING.
53
rods of Corfi {Co, Fig. 21), which are represented highly
magnified in Fig. 2'-t. These rods are stitf and arranged
side by side in two rows, leaned against one another by
tlieir npper ends so as to cover in a tunnel; they are known
respectively as the inner and outer rods, the former being
nearer the lamina spiralis. The inner rods are mere
numerous than the outer, the numbers being about GOOO
and 4500 respectively. Attached to the external sides of
the heads of the outer rods is the reticidar membrane (/•,
Fig. 2-2), whicli is stiff and perforated by holes. Exter-
nal to the outer rods come four rows of outer hair-cells,
connected like the inner row witli
nerve-fibres ; tlieir bristles project
into the holes of the reticular mem-
brane. Beyond the outer hair-cells
is ordinary columnar epithelium,
which passes gradually into cu-
boidal cells Uning most of tl!3 mem-
branous cochlea. F>*om the upper
lip of the sulcus spiralis projects
tlic tectorial mcmhraae {t, Fig, 21)
which extends over the rods of
Corti and the hair-cells'**
Tiie hair-cells would thus seem to
be tlie terminal organs for ' ])icking F,a. 23.— sensory ppithciinm
) ,\ -i L- I • 1 ii „ „:_ fmm ampulla op seniicircii
Up' the vibrations which the air- larcanai au.i saccui.' Am
waves communicate through all tlie ^.^'I^ill^li.lISiii":^:^!;!
iMlerveui..g api-aratus, solid and \^^::,:^';,:^}l^,,, ^\::,:,
iifiuid, to tlie basilar membrane, hair la show,,, th.- nerve ni)ie
I ' hfine hroken awav froi,, iii>
AiialoL'ous hair-cells receive the hase.' The ni^nder i;t'iis,ai
tertniiial nerve-filaments 111 tlio terves.
wallri of the eacciile, utricle, and aiiiitulhB (see Fig. 23).
The VariouB Qualities of Sound.— I'liysically, sounds con-
siet of vibraliouH. ami these are, generally speaking, nerial
wares. When the waves are non-periodic the result is a
Martin : op. eil
64 PSYCHOLOGY.
noise; when periodic it is what is nowadays called a tone,
or note. The loudness of a sound depends on the force of the
waves. When they recur periodically a peculiar quality
called jJiYc//. is the effect of their frequency. In addition to
loudness and pitch tones have each their voice or timbre,
which may differ widely in different instruments giving
equally loud tones of the same pitch. This voice depends
on the/orm of the aerial wave.
Pitch. — A single puff of air, set in motion by no matter
what cause, will give a sensation of sound, but it takes at
least four or five puffs, or more, to convey a sensation of
pitch. The pitch of the note c, for instance, is due to 132
vibrations a second, that of its octave c' is produced by twice
as many, or 264 vibrations; but in neither case is it ne-
cessary for the vibrations to go on during a full second
for the pitch to be discerned. " Sound vibrations may
be too rapid or too slow in succession to produce sonorous
sensations, just as the ultra-violet and ultra-red rays of
the solar spectruni fail to excite the retina. The highest-
pitched audible note answers to about 38,016 vibrations in
a second, but it differs in individuals; many persons cannot
hear the cry of a bat nor the chirp of a cricket, which lie
near this upper audible limit. On the other hand, sounds
of vibrational rate about 40 per second are not well heard,
and a little below this they produce rather a ' hum ' than a
true tone-sensation, and are only used along with notes of
higher octaves to which they give a character of greater
iepth." «
The entire system of pitches forms a continuum of one
dimension; that is to say, you can pass from one pitch to
another only by one set of intermediaries, instead of by
more than one, as in the case of colors. (See p. 41.) The
whole series of pitches is embraced in and between the
terms of what is called the musical scale. The adoption of
certain arbitrary points in this scale as * notes * has an ex-
• Martin : op. nU.
HEARING 55
planatioii partiv liistoric and partly lesthetic, but too com-
j)lex for ex]H)sition here.
The 'timbre' of a note is due to its wave-form. Waves
are eitlier simple ('pendular') or compound. Thus if a
tuning-fork (whicli gives waves nearly simple) vibrate 132
times a second, we shall hear the note c. If simultaneously
a fork of 204 vibrations be struck, giving the next higher
octave, (â– ', the aerial movement at any time will be tlie alge-
braic sum of the movements due to both forks; whenever
both drive the air one way they reinforce one another;
when on the contrary the recoil of one fork coincides with
tiie forward stroke of another, they detract from ea :h
otlicr's effect. The result is a movement whicii is still
periodic, repeating itself at equal intervals of time, but no
longer peiulular,' since it is not alike on the ascending and
descending limbs of the curves. "We thus get at the fact
that non-pendular vibrations may he produced by the fusion
of i)endular, or. in technical phrase, by their composiiion.
Suppose several musical instruments, as those of an or-
chestra, to be sounded together. Each produces its own
effect on the air-i)articles, whose movements, being an
algebraical sum, must at any given instant be very cona-
plex; yet the ear can pick out at will and follow the tones
of any one instrument. Now in most musical instruments
it is susceptible of physical proof that with every single
note that is sounded many upper octaves and other ' har-
monica ' sound simultaneously in fainter form. On tlie
relative strength of this or that one or more of these Ilelm-
liolta has shown that the instrument's peculiar voice de-
jtend-s. Tiie several vowel-sounds in the human voice also
depend on the predominance of diverse upper harmonics
accompanying the note on which the vowel is sung. When
the two tuning-forks of the last paragra])h are sounded to-
gether the new form of vibration has the Biime period as
the lower-pitched fork; yet the ear can clearly distinguish
the resultant sound from that of the lower fork alone, as a
note of the siimo pitch but of (liffcrent timbre; and within
(56 P8YGH0L00T.
the compound sound the two components can by a trained
ear be severally heard. Now how can one resultant wave-
form make us hear so many sounds at once ?
The analysis of compound wave-forms is supposed (after
Ilelmholtz) to be effected through the different rates of
sympathetic resonance of the different parts of the mem-
branous cochlea. The basilar membrane is some twelve
times broader at the apex of the cochlea than at the base
where it begins, and is largely composed of radiating fibres
which may be likened to stretched strings. Now the phy-
sical principle of sympathetic resonance says that when
stretched strings are near a source of vibration those whose
own rate agrees with that of the source also vibrate, the
others remainmg at rest. On this principle, waves of peri-
lymph running down the scala tympani at a certain rate of
frequency ought to set certain particular fibres of the basilar
membrane vibrating, and ought to leave others unaffected.
If then each vibrating fibre stimulated the hair-cell above
it, and no others, and each such hair-cell, sending a current
to the auditory brain-centre, awakened therein a specific
process to which the sensation of one particular pitch was
correlated, the physiological condition of our several pitch-
sensations would be explained. Suppose now a chord to
be struck in which perhaps tv/enty different physical rates
of vibration are found: at least twenty different hair-cells
or end-organs will receive the jar; and if the power cf
mental discrimination be at its maximum, twenty different
' objects ' of hearing, in the shape of as many distmct
pitches of sound, may appear before the mind.
The rods of Corti are supposed to be dampers of the
fibres of the basilar membrane, just as the malleus, incus,
and stapes are dampers of the tympanic membrane, as well
as transmitters of its oscillations to the inner ear. There
must be, in fact, an instantaneous da7npi?ig of the physio-
logical vibrations, for there are no such positive after-images,
and no such blendings of rapidly successive tones, as the
retina shows us in the case of light- Heloaholtz's theorv of
UKAlilNG. 67
the analysis of sounds is plausible and ingenious. One
objection to it is that the keyboard of the cochlea does not
seem extensive enough for the number of distinct reso-
nances required. We can discriminate many more degrees
of pitch than the 20,000 hair-cells, more or less, will allow
for.
The so-called Fusion of Sensations in Hearing. — A very
common way of explaining the fact that waves which singly
give no feeling of pitch give one when recurrent, is to say
that their several sensations fuse into a compoitnd sensatiun,
A preferable explanation is that which follows the analog}
of muscular contraction. If electric shocks are sent into a
frog's sciatic nerve at slow intervals, the muscle which the
nerve supplies will give a series of distinct twitches, one for
each shock. But if they follow each other at the rate of as
many as thirty a second, no distinct twitches are observed,
but a steady state of contraction instead. This steady con-
traction is known as tctaniix. The experiment proves that
there is a physiological cumulation or overlapping of })ro-
cesses in the muscular tissue. It takes a twentieth of a
second or more for the latter to relax after the twitch due to
the first shock. But the second shock comes in before the
relaxation can occur, then the third again, and so on; so
that continuous tetanus takes the place of discrete twitch-
ing. Similarly in the auditory nerve. One shock of air
starts in it a current to the auditory brain-centre, and