from destructive lesions within its limits. It has a special arterial
supply, viz. the middle cerebral, which divides into two main branches--an
anterior, which supplies the motor portion, and a posterior, which supplies
the posterior sensory portion. The anterior divides into two branches and
the posterior into three branches, consequently various limited portions of
the speech zone may be deprived of blood supply by blocking of one of these
branches. The speech zone of the left hemisphere directly controls the
centres in the medulla oblongata that preside over articulation and
phonation; innervation currents are represented by the arrows coming from
the higher to the lower centres.]
These several cortical regions are connected by systems of subcortical
fibres to two regions in front of the ascending frontal convolution (_vide_
fig. 17), called respectively the "glosso-kinæsthetic" (sense of movement
of tongue) and the "cheiro-kinæsthetic" (sense of movement of hand) centres.
Now a person may become hemiplegic and lose his speech owing either to the
blood clotting in a diseased vessel, or to detachment of a small clot from
the heart, which, swept into the circulation, may plug one of the arteries
of the brain. The arteries branch and supply different regions,
consequently a limited portion of the great brain may undergo destruction,
giving rise to certain localising symptoms, according to the situation of
the area which has been deprived of its blood supply. Upon the death of the
patient, a correlation of the symptoms observed during life and the loss of
brain substance found at the _post-mortem_ examination has enabled
neurologists to associate certain parts of the brain surface with certain
functions; but M. Marie very rightly says: None of the older observations
by Broca and others can be accepted because they were not examined by
methods which would reveal the extent of the damage; the only cases which
should be considered as scientifically reliable are those in which a
careful examination by sections and microscopic investigation have
determined how far subcortical structures and systems of fibres uniting
various parts of the cortex in the speech zone have been damaged. Marie
maintains that the speech zone cannot be separated into these several
centres, and that destruction of Broca's convolution does not cause loss of
speech (_vide_ figs. 16, 17). There are at present two camps--those who
maintain the older views of precise cortical centres, and those who follow
Marie and insist upon a revision.
Herbert Spencer says that "our intellectual operations are indeed mostly
confined to the auditory feelings as integrated into words and the visual
feelings as integrated into ideas of objects, their relations and their
motions."
Stricker by introspection and concentration of attention upon his own
speech-production came to the conclusion that the primary revival of words
was by the feeling of movements of the muscles of articulation; but there
is a fallacy here, for the more the attention is concentrated upon any
mental process the more is the expressive side brought into prominence in
consciousness. This can be explained by the fact that there is in
consequence of attention an increased outflow of innervation currents to
special lower executive centres, thence to the muscles, but every change of
tension in the speech muscles is followed by reciprocal incoming
impressions appertaining to the sense and feeling of the movement. The more
intense the sense of movement, the greater will be the effect upon
consciousness. In fact, a person who reads and thinks by articulating the
words, does so because experience has taught him that he can concentrate
his attention more perfectly; therefore his memory or understanding of the
subject read or thought of will be increased. Very many people think and
commit to memory by this method of concentrating attention; they probably
do not belong to the quick, perceptive, imaginative class, but rather to
those who have power of application and who have educated their minds by
close voluntary attention. Galton found a large proportion of the Fellows
of the Royal Society were of this motor type. But the fact that certain
individuals make use of this faculty more than others does not destroy the
arguments in favour of the primary revival of words in the great majority
of persons by a subconscious process in the auditory centre, which is
followed immediately by correlated revival of sensori-motor images.
Although the sensori-motor images of speech can be revived, it is almost
impossible without moving the hand to revive kinæsthetic impressions
concerned in writing a word. Both Ballet and Stricker admit this fact, and
it tends to prove that the sense of hearing is the primary incitation to
speech.
Charcot in reference to the interpretation of speech defects divided
persons into four classes--auditives, visuals, motors, and indifferents.
There are really no separate classes, but only different kinds of
word-memory in different degrees of excellence as regards the first three;
and as regards the fourth there is no one kind of memory developed to a
preponderating degree. Bastian doubts the second class, but does not deny
that the visual type may exist; for Galton has undoubtedly shown that
visual memory and power of recall of visual word images varies immensely in
different individuals, and it is unquestionable that certain individuals
possess the visualising faculty to an extraordinary degree; some few,
moreover, can see mentally every word that is uttered; they give their
attention to the visual symbolic equivalent and not to the auditory. Such
persons may, as Ribot supposes, habitually think and represent objects by
visual typographic images. Lord Macaulay and Sir James Paget were notable
possessors of this visualising faculty. The former is said to have been
able to read a column of "The Times" and repeat it _verbatim_; the latter
could deliver his lectures _verbatim_ as he had written them. Both saw
mentally the print or MS. in front of them.
Nevertheless it is a question of degree how much motor images enter into
silent thought and into the primary revival of words in different
individuals. Mach in "Analysis of Sensations" says: "It is true that in my
own case words (of which I think) reverberate loudly in my ear. Moreover, I
have no doubt that thoughts may be directly excited by the ringing of a
house-bell, by the whistle of a locomotive, etc., that small children and
even dogs understand words which they cannot repeat. Nevertheless I have
been convinced by Stricker that the ordinary and most familiar, though not
the only possible way, by which speech is comprehended is really _motor_
and that we should be badly off if we were without it. I can cite
corroborations of this view from my own experience. I frequently see
strangers who are endeavouring to follow my remarks slightly moving their
lips."
THE PRIMARY SITE OF REVIVAL OF WORDS IN SILENT THOUGHT
Since destructive lesions of the speech zone of the left hemisphere in
right-handed persons leads to inability to revive the memory pictures of
the sounds of words as heard in ordinary speech, the revival of visual
impressions as seen in printed or written characters, and of the
kinæsthetic (sense of movement) impressions concerned with the alterations
of the minute tensions of the muscle structures employed in the
articulation of words, it must be presumed that the left hemisphere in
right-handed persons is dominant in speech and silent thought; it may even
dominate the use of the left hand for many movements. But does not the
right hemisphere take a part? Yes; and I will give my reasons later for
supposing that the whole brain is in action. During the voluntary recall of
words in speech and thought by virtue of the intimate association tracts
connecting the grey matter of the whole speech zone, it is not a single
part of this zone which is in action, but the whole of it; and when we
assign to definite parts of the speech zone different functions in
connection with language, we really refer to areas in which the process is
most active or is primarily initiated, for the whole brain is in action
just as it is in the recognition of an object which we see, hear, feel, or
move. What really comes before us is contributed more by the mind itself
than by the present object.
There is, however, a direct functional association between the auditory and
glosso-kinæsthetic (sense of movement of the tongue) centres on the one
hand and the visual and cheiro-kinæsthetic (sense of movement of the hand)
on the other. No less intimate must be the connection between the auditory
word-centre and the visual word-centre; they must necessarily be called
into association actively in successive units of time, as in reading aloud
or writing from dictation. Educated deaf mutes think with revived visual
symbols either of lips or fingers. Words are to a great extent symbols
whereby we carry on thought, and thinking becomes more elaborate and
complex as we rise in the scale of civilisation, because more and more are
verbal symbols instituted for concrete visual images.
In which portion of the brain are words primarily and principally revived
during the process of thinking? I have already alluded to the views of
Stricker and those who follow him, viz. that words are the revived images
of the feelings of the sense of movement, caused by the alteration in the
tension of the muscles of articulation occurring during speech, with or
without phonation. There is another which I think the correct view, that
words are revived in thought primarily as auditory images, so that the
sense of hearing is essential for articulation as well as phonation; the
two operations of the vocal organ as an instrument of the mind being
inseparable. The arguments in favour of this are:--
1. The part of the brain concerned with the sense of hearing develops
earlier and the nerve fibres found in this situation are myelinated[1] at
an earlier period of development of the brain than the portion connected
with the sense of movement of the muscles of articulation.
[Footnote 1: The covering of the fibres by a sheath of phosphoretted fat
serving to insulate the conductile portion of the nerve is an indication
that the fibre has commenced to function as a conductor of nervous
impulses.]
2. As a rule, the child's first ideas of language come through the sense of
hearing; articulate speech is next evolved, in fact the child speaks only
that which it has heard; it learns first to repeat the names of persons and
objects with which it comes into relation, associating visual images with
auditory symbols.
An example of this was communicated by Darwin to Romanes. One of his
children who was just beginning to speak, called a duck a "quack." By an
appreciation of the resemblance of qualities it next extended the term
"quack" to denote all birds and insects on the one hand, and all fluid
objects on the other. Lastly, by a still more delicate appreciation of
resemblance the child called all coins "quack" because on the back of a
French sou it had seen the representation of an eagle (Romanes' "Mental
Evolution in Man," p. 183). Later on, children who have been educated
acquire a knowledge of the application of visual symbols, and how to
represent them by drawing and writing, and associate them with persons and
objects.
3. There is more definiteness of impression and readiness of recall for
auditory than for articulatory motor sense feelings.
4. After the acquirement of speech by the child, auditory feelings are
still necessary for articulate speech processes; for if it were not so, how
could we explain the fact that a child up to the fifth or sixth year in
full possession of speech will become dumb if it loses the sense of hearing
from middle-ear disease, unless it be educated later by lip language.
5. Cases have been recorded of bilateral lesion of the auditory centre of
the brain producing loss of hearing and loss of speech, the motor centres
being unaffected. This is called Wernicke's sensory aphasia. The following
case occurring in my own practice is probably the most complete instance
recorded.
CASE OF DEAFNESS ARISING FROM DESTRUCTION OF THE AUDITORY CENTRES IN THE
BRAIN CAUSING LOSS OF SPEECH
A woman at the age of twenty suddenly became unconscious and remained so
for three hours; on recovery of consciousness it was found she could not
speak; this condition remained for a fortnight; speech gradually returned,
although it was impaired for a month or more. She married, but soon after
marriage she suddenly lost her hearing completely, remaining permanently
stone deaf; and although she could understand anything of a simple
character when written, and was able imperfectly to copy sentences, she was
unable to speak. Once, however, under great emotional excitement, while I
was examining her by written questions, she uttered, "Is that." But she was
never heard to speak again during the subsequent five years that she lived.
The utterance of those two words, however, showed that the loss of speech
was not due to a defect of the physiological mechanism of the vocal
instrument of speech, nor to the motor centres in the brain that preside
over its movements in the production of articulate speech. She recognised
pictures and expressed satisfaction or dissatisfaction when correct or
incorrect names were written beneath the pictures; moreover, in many ways,
by gestures, facial expression, and curious noises of a high-pitched,
musical, whining character, showed that she was not markedly deficient in
intelligence. Although in an asylum and partially paralysed, she was not
really insane in the proper sense, but incapable of taking care of herself.
When other patients were getting into mischief this patient would give a
warning to the attendants by the utterance of inarticulate sounds, showing
that she was able to comprehend what was taking place around and reason
thereon, indicating thereby that although stone deaf and dumb, it was
probable that she possessed the power of silent thought. I observed that
during emotional excitement the pitch of the sounds she uttered increased
markedly with the increase of excitement. After having been discharged from
Claybury Asylum she was sent to Colney Hatch Asylum. Upon one of my visits
to that institution I learnt that she had been admitted, and upon my
entering the ward, although more than a year had elapsed since I last saw
her, she immediately and from afar recognised me; and by facial expression,
gesture, and the utterance of inarticulate sounds showed her great pleasure
and satisfaction in seeing one who had taken a great interest in her case.
This poor woman must have felt some satisfaction in knowing that someone
had interpreted her mental condition, for of course, her husband and
friends did not understand why she could not speak. I may mention that the
first attack of loss of speech was attributed to hysteria.
This woman died of tuberculosis seven years after the second attack, and
examination of the brain _post-mortem_ revealed the cause of the deafness.
There was destruction of the centre of hearing in both hemispheres (_vide_
fig. 17), caused by blocking of an artery supplying in each hemisphere that
particular region with blood. The cause of the blocking of the two arteries
was discovered, for little warty vegetations were found on the mitral valve
of the left side of the heart. I interpreted the two attacks thus: one of
these warty vegetations had become detached, and escaping into the arterial
circulation, entered the left carotid artery and eventually stuck in the
posterior branch of the middle cerebral artery, causing a temporary loss of
word memory, consequently a disturbance of the whole speech zone of the
left hemisphere. This would account for the deafness to spoken language and
loss of speech for a fortnight, with impairment for more than a month,
following the first attack. But both ears are represented in each half of
the brain; that is to say, sound vibrations entering either ear, although
they produce vibrations only in one auditory nerve, nevertheless proceed
subsequently to both auditory centres. The path most open, however, for
transmission is to the opposite hemisphere; thus the right hemisphere
receives most vibrations from the left ear and _vice versa_. Consequently
the auditory centre in the right hemisphere was able very soon to take on
the function of associating verbal sounds with the sense of movement of
articulate speech and recovery took place. _But_, when by a second attack
the corresponding vessel of the opposite half of the brain was blocked the
terminal avenues, and the central stations for the reception of the
particular modes of motion associated with sound vibration of all kinds
were destroyed _in toto_; and the patient became stone deaf. It would have
been extremely interesting to have seen whether, having lost that portion
of the brain which constitutes the primary incitation of speech, this
patient could have been taught lip language.
There is no doubt that persons who become deaf from destruction of the
peripheral sense organ late in life do not lose the power of speech, and
children who are stone deaf from ear disease and dumb in consequence can be
trained to learn to speak by watching and imitating the movements of
articulation. Helen Keller indeed, although blind, was able to learn to
speak by the education of the tactile motor sense. By placing the hand on
the vocal instrument she appreciated by the tactile motor sense the
movements associated with phonation and articulation. The tactile motor
sense by education replaced in her the auditory and visual senses. The
following physiological experiment throws light on this subject. A dog that
had been deprived of sight by removal of the eyes when it was a puppy found
its way about as well as a normal dog; but an animal made blind by removal
of the occipital lobes of the brain was quite stupid and had great
difficulty in finding its way about. Helen Keller's brain, as shown by her
accomplishments in later life, was a remarkable one; not long after birth
she became deaf and blind, consequently there was practically only one
avenue of intelligence left open for the education of that brain, viz. the
tactile kinæsthetic. But the tactile motor sense is the active sense that
waits upon and contributes to every other sense. The hand is the instrument
of the mind and the agent of the will; consequently the tactile motor sense
is intimately associated in its structural representation in the brain with
every other sense. This avenue being open in Helen Keller, was used by her
teacher to the greatest possible advantage, and all the innate
potentialities of a brain naturally endowed with remarkable intellectual
powers were fully developed, and those cortical structures which normally
serve as the terminal stations (_vide_ fig. 16) for the reception and
analysis of light and sound vibrations were utilised to the full by Helen
Keller by means of association tracts connecting them with the tactile
motor central stations. The brain acts as a whole in even the simplest
mental processes by virtue of the fact that the so-called functional
centres in the brain are not isolated fields of consciousness, but are
inextricably associated one with another by association fibres.
THE PRIMARY REVIVAL OF SOME SENSATIONS IN THE BRAIN
I have on page 77 referred to Stricker's views on the primary revival of
words in the sense of movement of the lips and tongue. Mach ("Analysis of
the Sensations") says: "The supposition that the processes in the larynx
during singing have had something to do with the formation of the tonal
series I noticed in one of my earlier publications, but did not find it
tenable. Singing is connected in too extrinsic and accidental a manner with
hearing to bear out such an hypothesis. I can hear and imagine tones far
beyond the range of my own voice. In listening to an orchestral performance
with all the parts, or in having an hallucination of such a performance, it
is impossible for me to think that my understanding of this broad and
complicated sound-fabric has been effected by my _one_ larynx, which is,
moreover, no very practised singer. I consider the sensations which in
listening to singing are doubtless occasionally noticed in the larynx a
matter of subsidiary importance, like the pictures of the keys touched
which when I was more in practice sprang up immediately into my imagination
on hearing a performance on the piano or organ. When I imagine music, I
always distinctly hear the notes. Music can no more come into being merely
through the motor sensations accompanying musical performances, than a deaf
man can hear by watching the movements of players. I cannot therefore agree
with Stricker on this point" (comp. Stricker, "Du langage et de la
musique," Paris, 1885).
Of the motor type myself and having a fairly good untrained ear for music,
I find that to memorise a melody, whether played by an instrument or by an
orchestra, I must either try to sing or hum that melody in order to fix it
in my memory. Every time I do this, association processes are being set up
in the brain between the auditory centres and the centres of phonation; and
when I try to revive in my silent thoughts the melody again, I do so best
by humming aloud a few bars of the melody to start the revival and then
continuing the revival by maintaining the resonator in the position of
humming the tune, viz. with closed lips, so that the sound waves can only
escape through the nose; under such circumstances the only definite
conscious muscular sensation I have is from the effect of closure of the
lips; the sensations from the larynx are either non-existent or quite
ill-defined, although I hear mentally the tonal sensations of the melody.
No doubt by closing the lips in silent humming I am in some way
concentrating attention to the sensori-motor sphere of phonation and
articulation, and by reactive association with the auditory sphere
reinforcing the tonal sensations in the mind. The vocal cords (ligaments)
themselves contain very few nerve fibres; those that are seen in the deeper
structures of the cords and adjacent parts mainly proceed to the mucous
glands. This fact, which I have ascertained by numerous careful
examinations, is in accordance with the fact that there are no conscious
kinæsthetic impressions of alterations of position and tension of the vocal
cords. A comparative microscopic examination of the tip of the tongue and
the lips shows a remarkable difference, for these structures are beset with
innumerable sensory nerves, whereby every slightest alteration of tension
and minute variations in degrees of pressure of the covering skin is
associated with messages thereon to the brain. The sense of movement in
articulate speech is therefore explained by this fact. There is every
reason then to believe that auditory tonal images are the sole primary and
essential guides to the minute alterations of tension in the muscles of the
larynx necessary for the production of corresponding vocal sounds. By
humming a tune we concentrate our attention and thereby limit the activity
of neural processes to systems and communities of neurones employed for the
perception of tonal images and their activation in motor processes; and
this helps to fix the tune in the memory.
PSYCHIC MECHANISM OF THE VOICE