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Efferent nerves to the inner ear: a First Approach
Rasmussen "The olivary peduncle and other fiber projections of
the superior olivary complex", 1946 ;
- Rasmussen et al
"Neural Mechanisms of the Auditory and Vestibular Systems",
- Warr "Olivocochlear and vestibulocochlear
efferent neurons of the feline brain stem: their location, morphology
and number determined by retrograde axonal transport and
acetylcholinesterase histochemistry", 1975 ;
"Morphology of labeled efferent fibers in the guinea pig
cochlea", 1987 ;
- Wolff "Efferente
Aktivatät in den Statonerven einiger Landpulmonaten (Gastropoda)",
- Ryugo et al "Auditory and Vestibular Efferents",
- Goldberg et al " The Vestibular System: A Sixth
The idea that the brain could influence how
its sensory receptors work is very difficult to accept. We can
understand that organisms can choose what to direct their attention
on and what not, but just as we cannot not hear, we cannot not see or
not feel something touching our skin.
Nonetheless, it is this
principle which has been put in doubt since many decades, even if it
seems to have had no practical consequences at all. At least, I do
not know of any article that goes beyond establishing this "fact",
accompanied by some platitudes about why Evolution saw it fit to
develop such a mechanism. But how such efferent neurons could
function is anybody's guess.
This seems like a perfect place
for George to build a nest [okay, home, have it your way].
Stimulation of the hair-cells in the semi-circular canals and
otholitic organs is supposed to be mechanical. Head movements result
in fluid movement that finaly hyper- or de-polarizes the receptors.
could understand the logic behind efferent neurons stimulating the
afferent cells of the receptors. Modulation of the effects of the
mechanical stimulation could, with great difficulty I might
add, be seen as an evolutionary precaution whose usefullness still
has to be established.
But what could efferent neurons possibly
have for effect on the receptor-cells themselves? The hair-cells
represent translational and gravitational on one side, rotational
effects on the other side. What would the efferents neurons
represent? What would the modulation of these effects look like? Less
rotation or less translation? Less gravity?!
The idea of
sensory modulation is not as strange as it might appear in the first
place. We can partially close our eye lids, or squint, to regulate
the amount of light impinging on our retina. We sweat or shiver to
counter the effects of temperature. The first type is purely
voluntary while the second would be considered more as a biological
reflex on which we have no direct influence.
Why not a modulation
of cochlear and vestibular stimulations? In the case of auditive
stimulation we can easily find all kind of logical arguments in favor
of such a mechanism. A better use of attentional processes would be
high on the list.
I honestly can think of no advantage of the
modulation of vestibular stimulations, or at least, those that I can
think of seem to be the wrong ones. It would be very advantageous for
an organism to counter the effects of involuntary rotation. Falling
in a swollen river and being tossed in all directions by the water is
a situation where a'cool" head could mean the difference between
life and death. And what about being shaken violently by a predator
and slipping from its jaws? Would it not be a blessing if the prey
could run away as soon as it fell on the ground, instead of feeling
dizzy and disoriented?
How about going to the fare with your
grandchildren and getting on one of those horrible rotating devices
which they love so much? I would immediately sign for such a
But alas! It is not to be. Whatever these
efferent neurons are doing to hair-cells, it is nothing so obviously
Vestibular modulation would only make sense in
situations where the brain can anticipate vestibular stimulation. Not
only that, the brain would need to know in advance what kind of
stimulation it will be getting: is it a simple head movement, or a
Otherwise, the brain might be modulating
stimulations that would be best kept unaldurated for the right
reactions to follow.
But such a distinction seems very unlikely.
If it were possible, nobody would ever get sea sick!
The fact that
we finally can learn to cope with the boat movements could mean that
the modulation process is itself a learning process that takes time
to settle in and show its fruits.
But modulating the way we
experience gravity and movements would also have consequences on the
way we run, walk or stand. The body needs those sensations to be
authentic at all times. It would be like the brain deciding to
modulate vision and reduce our sensitivity to blue in the summer
because of the cloudless sky. Maybe it does just that, but certainly
not by changing how visual cells react to different colors at the
saccadic suppression revisited
blindness occurs not only during eye movements, but during fixation.
We would be looking straight at the change and not see it because it
happened when we were not looking, and we are still relying on our
If we always "see" the content of our memory and
not the world itself, our vision does not need to be suppressed at
any moment. A change attracts our attention, we fixate on it and
record it in memory. And that is the moment we 'see it".
one happens before the other or simultaneously does not seem to be
really important in this context. Anyway, that is a question I would
not know how to answer: do we record it first and then see it, or
vice versa? The first alternative would be more in line with the idea
that we see what we remember, but maybe it does not apply to the
first time a change is perceived.]
What we therefore need to
explain is not a, probably, inexistent phenomenon (vision suppression
during eye movement), but a real phenomenon: change blindness, or
rather its positive correlate, change perception.
taught us that we can only be conscious of acceleration and not of
motion itself. Maybe the same rule applies to vision: we can only see
That is why we can see the blur in movies, and not in
real life. The first one is an objective phenomenon, the result of
chemical (emulsion sensitivity), or mechanical processes (shutter
speed). Whatever the reasons, it really exists independently from our
perception processes. A blur in real life would mean that objects
move faster than light, which physicists consider impossible,
certainly for everyday processes. Such a blur can therefore only be
produced by our own perception.
What is VOR? And does it really exist?
relationship between eye and head movements is always considered in a
so-called occulo-vestibular context.
stimulation of inner ear ---> vision constraints--> eye.
you can see, the relationship is a very complicated one. We are very
far from the doll'eyes paradigm which assumes a simple linear
relationship between both organs.
This is by the way what an
online textbook from Dartmouth Medical School has to say on this
"If the patient is awake [the brain] keeps the eyes
from deviating from midposition and actually may drive the eyes
beyond the midposition toward the direction of turning. If the
patient is in a coma due to bilateral hemispheric suppression [...]
the eyes deviate away from the direction of head rotation in an
unchecked manner (the reflex response is not inhibited by cerebral
cortical input)." (Reeves and Swenson "DISORDERS OF THE
NERVOUS SYSTEM". https://www.dartmouth.edu/~dons/index.html.
So, if there ever was a doubt as to the link between head
and eye movements, the reaction of coma patients should take it away.
What such examples do show is that, just like in the case of Mach's
experiments, visual constraints play no role whatsoever in this
We have though, instead of
movement --> stimulation of inner ear---> NO eye movement.
[A case of the so-called VOR cancellation. Remark that
such a concept turns VOR into something like the Freudian concept of
"resistance". It can never be falsified. Whatever the
patient says the therapist does not like can be interpreted this way,
and in all impunity. The same way, whenever a phenomenon does not
seem to support the existence of VOR, just put it under the heading
of VOR-cancelation, and you are good to go.]
movement --> stimulation of inner ear---> eye movement.
It seems impossible to make the line any shorter since
any head movement would have a stimulation of the inner ear as a
A very hard proof, for those, like me, who
doubt this trinity, is the so-called Barany's caloric test for
which he received the Nobel prize in 1914.
In fact, this test is
considered so reliable that it is one of the tests used to establish
Its simplicity is equaled only by its beauty [or the
other way around.]: pour some water, warmer or cooler than the body
temperature, in one of the inner ears, and a nystagmus will be
produced, its direction depending on whether it was cold or warm
(Following the COWS mnemonic: Cold Opposite Warm
Remark that we did shorten the line which has now
stimulation of inner ear --> eye movement
that seems like a definite proof that vestibular sensations and eye
movements are causally related.
But here is "le hic",
as the French would say. People undergoing the caloric test are
subject to vertigo. And the problem with vertigo, or dizziness, is
that it is, usually, not a very nice sensation. It is somehow
comparable to pain.
withdrawal reflex is said to come into action before we even have the
time to feel pain. It is therefore purely mechanical. How about
jumping up and down and bringing your hurt finger to your mouth? What
is the neuronal cause of this behavior? You could look for pain in
the brain as long as you want to, you will not find it.
armed with science-fiction technology that would allow him to follow
the excitation of each individual nerve in situ, that is with full
consideration of the context in which it is happening, would probably
see two series of events follow each other, but with no apparent link
action one - gap - action two
paradigm would be a very clear representation of causal efficacy of a
It is indicative for the Zeitgeist that a
concept like emergence has been accepted so easily because it could
hitch a ride with modern concepts like "computer", "neuron"
and "complexity" that could hide its metaphysical roots,
while the concepts of spontaneous generation or mental causality are
action one - emergence of a link - action
action one - spontaneous generation of a link - action
action one - sensation/emotion - action two
I must say
that of all three realizations of the same paradigm, the last one has
at least the plausibility of psychological phenomena.
worried that the acceptance of causal efficacy for mental events
would open the dam wide open to all kinds of mystical pretensions,
which would of course certainly happen. But do not think for a second
that the mystics would then get a free lunch.
The physical realm
cannot solve the halting problem, it needs for that the mental realm.
But does that mean that the mental realm is "computationally"
or "logically" complete? [Whatever those terms may mean in
Or will the mental realm also need the physical
realm to be effective?
The previous paradigm would then
Sensation/Emotion - gap - Sensation/Emotion
what could fill in the gap better than the physical realm? We would
Sensation/Emotion - physical action -
In other words, you cannot go indefinitely
from sensation to sensation, you need the in-between stops in the
physical realm to access other sensations. [we can go from pain to
relief only if the effects of pain are taken away. And that is a
physical process. Without that, we would probably witness something
akin to inertia: the pain would never stop, just like an object put
in motion can never stop out of itself!]
We would end up with
what we already have, a physical and a mental realm. No harm
What makes the gap nigh invisible is its familiar
nature. We see no gap between the behavior of someone burning his
finger, withdrawing his hand, and jumping up and down. Why would we
see it in the neural version of this series of events?
take a very thorough knowledge and mapping of the brain to discover
the gap. Without this scientific certainty, that may never be
attained, that two successive events are not causally related, we
will always fill in the gap ourselves.
Of course, such speculative
considerations may turn out to be superfluous.
Simpler Explanation is
maybe given by
Baloh and Honrubia's "Clinical
Neurophysiology of the Vestibular System", 2010:
the spontaneous afferent nerve activity increases and decreases
because of heating and cooling of the afferent nerve, respectively."
Which means in fact that the caloric test is nothing else
but a surrogate vestibular stimulation.
We are therefore
back to the previous situation:
head movement -->
stimulation of inner ear---> eye movement
stimulation --> stimulation of inner ear---> eye movement
metaphysical digression was after all maybe not so superfluous?
us if we can find more down to earth arguments.
Are eye movements and vestibular stimulation causally related?
according to Mach'experiments, and certainly not according to our
very own everyday experiences. We do not get a doll's eyes reflex
when going up or down in an elevator, and air pilots seem to be very
well capable or repressing any occulo-vestibular reflexes they may
have. This was known even before World War II as vestibular
habituation: (Griffith "The organic effects of repeated bodily
rotation", 1920; Dodge "Habituation to rotation",
Furthermore, there is no unequivocal proof of a direct link
between the inner ear afferents and the extra-ocular motoneurons,
the topological concept of vestibular nuclei notwithstanding. All
evidence is circumstantial and could be very easily interpreted
differently. Which I certainly will.
All in All, there is no
reason to blindly accept the existence of such a link.
doing away with VOR might turn out to be very beneficial for further
research. After all, more than a century of experiments after Mach
have still not given any final results that could satisfy everybody.
Researchers are still playing with Barany chairs and arguing about
meaningless numbers and other quantitative models. And it does not
look like they will stop any time soon!
In his Nobel Lecture
(1914) Barany spoke of different tests that showed the links of the
inner ear neurons not only with the extra-ocular muscles, but also,
via the cerebellum, with practically all body muscles.
on vestibular malfunctions on balance and posture were already known,
Flouren's predilection for methodical ablations of different layers
of neurons in the cerebellum and elsewhere having given convincing
results which had been confirmed by others.
Experimentales sur les Proprietes et les Fonctions du systeme nerveux
dans les Animaux Vertebres", 1842.]
What I find
particularly illuminating in the examples given is the complexity of
the connections between vestibular neurons and other parts of
the nervous system.
Let us take the simple example of telling the
patient to hold his right arm straight and then "syringe"
his right ear with cold or warm water. The arm, inexorably, starts
deviating from its position.
The deviation is even more noticeable
when the patient is asked to touch with his own fingers those of the
doctor. His fingers will deviate to the right or the left, opposite
to the nystagmus that had been caused by the caloric
Here is "anozer 'ic":
stimulation can apparently have an effect on many muscles whatever
their initial position. Barany speaks of the different joints at the
wrist, elbow, hip [no George, not 'ip, hip. We must not abuse of a
good thing!], etc.
That is a lot of branching, which must also
involve a lot of logic to make sure that when the same vestibular
neurons are activated, the right muscles, according to the situation
and context, are innervated .[Shall it be the eye AND the cerebellum,
or the eye alone? Would you like a gift wrapping?]
conception of a direct connection between stimulation of the inner
ear and so many different muscles is untenable. Other, more complex,
neural mechanisms must be involved. And if that is the case, how can
we still speak of "reflexes"?
Retinal Image and its Movements
must admit that I have great difficulties at times following the
argumentation of different authors, starting from the pioneers of the
19th century. This is my problem:
A retinal image can be compared
to a drawing on the inside of a globe. however the globes moves, the
image will move with it, whatever rotation the globe does, the image
will rotate ccordingly... In space... If we make abstraction of the
What about torsional movements. Can the retinal image turn
around its own axis if the globe does the same thing? Again, if we
make abstraction of the globe, we can only conclude that the image
will have rotated about its own axis: it will have performed a
Here is the problem as I see it: the globe,
that is the eye, can be said to rotate and even translate in space...
If we make abstraction of the head! Otherwise, we can say that the
eye can go left-right and up-down. Even the so called rolling of
one's eyes is in fact a combination of the previous
Listing's plane is the mathematization of this
intuition. We cannot move or turn our eyes in 3D space, only in a 2D
Let us use the ancient Greek conception of the eyes
being the origin of the light we direct on external objects to see
them: the electric torch paradigm.
Do we have to imagine the torch
fastened to a system of horizontal and vertical rails on a wall
(Listing's plane), or a torch fastened to a mobile wall that can be
moved up and down, but also be tilted forward or backward?
about tilted to the left or right side? Can the eye do that?
suppose that all tilted positions can be attributed to the eye in a
stationary head, while all translations can be seen as the result of
the head and or the body moving. [Helmholz about the way the eye is
fixed in its orbit: "any displacement of the eyeball as a whole,
that is, any displacement in which every point of the eyeball is
moved in the same direction, is rendered impossible." Treatise,
The problem is that the eye cannot be tilted from
its place. It can only be rotated. So, instead of a wall, maybe a
hand holding a torch would bring us closer to how the eye behaves.
we need different concepts for the eye movements in this second case.
Can we say really that the eyes move from left to right or up and
down, just because the head itself is moving?
after-image paradigm, what is calculated, the retinal image, or the
visual sensation as after-image?
The retinal image can be said to
perform any movement, and not only torsion, only in an abstract,
geometrical way. As part of the eye globe it just follows passively
the movements of the latter, while in fact remaining stationary.
is calculated is not the position in space of an external, observable
object, but that of an internal, private visual sensation.
somehow back to the Weberian paradigm, aren't we?
seems to be the case, at least until the calculations are suddenly
transferred to another dimension.
The movements of the after image
are not used to analyze how your sensations behave in different
circumstances, but to justify calculations where they are completely
ignored and neutralized. Optical laws in the modern version do not
need to mention visual sensations at all. Even the use of
after-images has made place for the neutral calculation of eye
movements with magnetic and electrical devices.
Efferent nerves to the inner ear: a possible explanation
difference between vestibular sensations and sensory organs is that
the first is oriented at signals from within the body, while the
others warn the body about any external intrusion.
sitting in my favorite, old but comfortable swivel chair which was,
once again, leaning a bit to the side. Time to re-fasten the feet
after shoving them back in the right position. But then I started to
think about this unremarkable fact: I could feel that the chair was
misaligned, and I could feel it everywhere but in my head. And, after
all, why should i feel it in my head? My head was straight on my
shoulders, it was the rest of my body that felt somewhat askew.
I understood, or thought I did, why the inner ear would need
efferents from other parts of the body. It has to know when it is out
of balance even if the head is straight, and therefore silent.
comparison with vision was the wrong one. In this case, it seems that
the brain was entitled to change the sensibility to blue (read
balance) if blue was too dominant. And that had to happen at the
source, in the inner ear. It would be indeed like changing the
sensibility of the retina to a certain color, but then, in this case,
the retina is directed directly and only to the own body. And the
inner ear needs authentic sensations from every part of our body.
does it work exactly? I have no idea.
Binocular vision and its myths
wrote his famous paper "On Physiological vision" in 1838,
one year before Daguerre published his results on the ancester of
photography and cinema. The steroscope Wheatstone described must have
seemed as a wondrous instrument, capable of bringing to life dead
objects! It also created quite a commotion among physiologists,
especially in Germany, where the discipline was approaching its peak
under giants like Messner, Mueller and others, all soon to be
eclipsed by Helmholz and Hering.
At that time, the Theory of the
Identity of Retinal Images was predominant. One assumed that the only
way binocular single vision could be attained was by the fusion of
two similar images falling on corresponding locations in both
retinas. Albrecht Nagel ["Das Sehen mit zwei Augen", 1861;
not to be confused with the American batman], quotes Volkmann who
predicted the fall of the discipline and the repudiation of all the
calculations made possible by Mueller, Panum and others. Nagel, more
optimistic, and a fervent follower of Helmholz' empiricist approach,
promised that the situation was not as dire as it seemed. We were
witnessing a painful paradigm shift and Nagel was the
Nowadays, Wheatstone's view of binocular disparity has
become common knowledge, and whole industries (optics, cinema) are
based on his analysis. Still, it looks more like a Pyrrhic victory
than a technical knockout.
The Theory of the Identity of Retinal
Images has not been abandoned, as one would expect, but has
surreptitiously hidden behind its victor, thereby guaranteeing its
Before I turn to that, I would like to look more closely
at Wheatstone's approach.
disparity and its significance
gives two very interesting examples to introduce the stereoscope. The
second one gets a very thorough analysis as it is at the base of his
invention: two plane drawings, we would say 2D descriptions, are
presented in the stereoscope with as unexpected result a life-like
impression of a real spatial object.
More interesting is the first
example of two identical, real three dimensional objects, viewed
simultaneously through separate tubes, the way we would use
binoculars, but then without the common point of fixation.
is of course intent on promoting his new device, and only uses this
first example to illustrate the principle behind the main course.
Strangely enough, and as far as I know, nobody since then has ever
stood still by the significance of this first example. After all, it
was the physical embodiment of a contradictory principle to what
Wheatstone was trying to prove. Looking at two three-dimensional
objects also gave a three dimensional sensation. So, where does that
leave the theory of binocular disparity and Julesz' random-dot
stereograms("Foundations of Cyclopean Perception",
The conclusion that two, minimally dissimilar,
two-dimensional objects create the three-dimensional impression of a
single object, is of course undeniable. It only becomes subject to
doubt when used as the explanation of how 3D vison works. The
assumptions on which it is based are quite strange, to say the
It assumes that each eye sees the world as two-dimensional.
According to Nagel, and conform Helmolz's conception, when we look
with one eye, we still see objects as three-dimensional, because that
is the way we have learned to see them. A nice example of perception
as inference. Also, a theory which one either accepts or rejects,
because it can neither be disproved nor proven.
What is really
interesting though is whether the third dimension is a real property
of space or an illusion created by the brain for its own benefit. Do
we see objects in three dimensions because there are three
dimensions, or is the world in fact as flat as, or even more so than,
ancient earth? The answer to this question should determine how
seriously we take the theory of binocular disparity.
If space is
three dimensional why would we need such a complicated detour to
experience it as such? More to the point, why should the experience
of the third dimension, if it does indeed exist, be considered as an
illusion brought about by habits and learning?
In other words, the
theory of binocular disparity, as advocated by Nagel (and not
Wheatstone) and every author after him, only makes sense if space is
two-dimensional, and depth an illusion!
The Theory of the
Identity of Retinal Images had apparently to undergo a serious
change, that might end up to be strictly cosmetic. It was saved by
Panum's analysis of the horopter ("Physiologische Untersuchen
über das Sehen mit zwei Augen",1858), first mentioned in the
eleventh century by Ibn Al Haitham, and since then many times
recalculated until the concept lost any meaning. Almost a century ago
Danville in "The psychological significance of the horopter"
(1933) drew attention to the fact that all the approaches to the
horopter were geometrical, and giving different results because of
different starting points. The difficulty in establishing a clear
criterion had still not been solved in his time, as is also still the
case today. He tried for a psychological approach where he tried to
determine when humans experienced a single object as double. He found
out that the theoretical delimitations of the horopter were of little
use. Nowadays researchers speak of a theoretical and an empirical
horopter. But the idea that there is one or more areas where both
retinal inputs are seen as one, and others where a single object is
seen as double. has not lost its attraction.
I have certainly no
objection against such empirical assumptions that can be investigated
scientifically. What I find less obvious are the theoretical
prejudices that usually accompany such experiments.
The idea that
the brain somehow not only needs corresponding images on both
retinas, but also is capable of actively searching for them is, like
I said elsewhere, a typical homunculus approach.
Let us take the
example of two dissimilar images sent to each retina. Let us say, one
object inclined to the left, the other to the right. Apparently, in
such a case, the brain would try to somehow make fusion possible by
rotating the eyes (cyclorotation) in an appropriate way, that is by
limiting the disparity between both images.
George, Im' getting to it!]
The idea that the brain somehow knows
what to do so that both images on the retinas could be considered as
one is one of the most ludicrous assumptions that could ever be made.
Still, the number of articles containing complex mathematical
calculations and models is still growing.
What is even more
puzzling is that not a single article I read can in fact give an
example of factual cyclorotation. All conclusions are based on
geometrical models that predict eye movements and rotations (Hausen
"Considerations on Listing’s law and the primary position
means of a matrix description of eye position control",
1989). And even if they did somehow describe real cyclorotational
movements, that would still not necessarily have to be explained by
the need for the brain to bring two images together. It could as
easily be explained by the fact that each eye is trying to keep focus
of the image it is seeing, independently of what the other eye is
doing. A kind of smooth pursuit as it were, around the own
Goodenough et al "Eye torsion in response to a tilted visual
- Mok et al "Rotation of Listing’s
plane during vergence", 1992.
- Van Rijn and Van Den Berg "
Binocular eye orientation during fixations: Listing’s law to
include eye vergence", 1993.
- Minken and Van Gisbergen "A
three dimensional analysis of vergence movements at various levels of
- Howard and Rogers "Binocular Vision
and Stereopsis", 1995
- Hooge and Van Den berg "Visually
Evoked Cyclovergence and Extended Listing’s Law",
brains, binocular disparity and cyclorotations Oh la la!
last point (two disparate images presented to the brain and its
reaction) reminds me of an urban myth that has surrounded Kim Peek
for years, the model for Dustin Hoffmann's Rain Man. Many a writer on
the web shamelessly affirms that Peek was capable of reading two
books, or two pages, at the same time. Except the fact that neither
Peek nor his father ever admitted to such a feat, a simple
observation of Peek on the many videos on the web, while he is
reading, shows him as looking (incredibly) rapidly at one page, and
then the other. As somebody without a corpus callosum, Peek'brain was
comparable to that of patients who had had the connection between
both hemispheres disconnected to help them with their epileptic
Gazzaniga, the world's expert on splitbrains [even if his
boss, Sperry, took all the credit with the Nobel Prize of 1981, at
least that is the impression I got reading "Tales from Both
Sides of the Brain", 2015, the author's declaration of loyalty
notwithstanding] has a very interesting theory concerning the
communication between both, isolated, hemispheres. Let us see if we
can make use of it with our problem of binocular vision.
formulated already in his article of 1969 “Cross-cueing mechanisms
and ipsilateral eye-hand control in split-brain monkeys”, Gazzaniga
is convinced that both hemispheres are still able to communicate with
each other, even in the case by monkeys, where the ablation of the
interconnections is much more radical than by humans.
specific way of communication is what he calls auto-ceuing. One
hemisphere would initiate certain movements (head, eyes, body) to tip
the other over what was going on.
The question is, how does the
other hemisphere know what to do with the cues? Communication demands
a common language and a common subject on which to communicate. He
gives the example of one hemisphere having to push some lever but not
knowing which, and the other hemisphere signaling by its head and
eye movements which lever to push. Restraining the head made cueing
as good as impossible, and the responses dropped to chance
What does that prove?
To Gazzaniga, the
existence of communication channels between hemispheres that are
independent of the corpus callosum. Also, he is convinced that, even
if he considers speaking of two different minds in the same body as
going too far, the brain is made of a multitude of modules that work
independently of each other, but that communicate somehow via this
cueing process. A non-linguistic module will obviously need to get
non linguistic cues to be able to decipher them, and other modules,
just like in the example given, gladly comply.
This is a very
interesting view that is I am afraid much too general to be
falsifiable. So, I will leave it to those who can use it better than
me. [better than I? George, you are not British, are you?]
to the main question. All modules must be "conscious" of
the same situation and have the same goal. In our example, one
hemisphere could cue the other if it knew what was expected from its
twin. And the latter had to assume that the attempts to communication
were related to the problem at hand, and not to the fact that its
sibling was bored with the whole thing.
However you look at it, I
would say that there was only one mind which had to make use of
disconnected parts of his brain, and had somehow to improvise each
time to get things done. If we consider the hemispheres as the
repository of all the experiences the individual had had in his life,
we could say that activating one hemisphere or the other brought
different aspects of the same mind to the fore. A mind which we
could, with exaggeration, consider as a kind of tabula rasa that gets
written on separately each time by one of the hemispheres.
George, you're up!
in cases like this I have to be very careful. See, each time I am in
a hemisphere, I am caught in its world and know only what it knows,
and can do only what it can do. Then I get called by the other
hemisphere, and I do not forget where I had been, I even could
remember what I was doing. Sort of. I mean, I still knew how I felt,
I just could not remember how to do what I wanted to do.
you mean you had the know-what but not the know-how?
let us say that you hear a story from hemisphere A, sorry I can never
remember which does what, you understand then the story, but when you
get to B, you still know the sory, only this time, it is not in any
language that B can understand, or even in the language that A told
it in, so you have no way of telling it to B.
That's it! Are you sure you are not one of us?
you are one of me! And don't you forget it![mumble mumble].
other words, there is common information to both hemispheres, and
each hemisphere can be used by George separately, but George has no
influence whatsoever on the content in each hemisphere. It can only
make the best of it, wherever it is.
The link between both
hemispheres can of course be put on the conto of sub-cortical
connections, the question remains what these neural connections can
convey. Gazzaniga speaks of emotions but he does that in the
traditional way, as neural substrates in the form of a limbic system.
I go beyond that and surmise that there is another dimension which is
served by these neural substrates, and which make those emotions
accessible to the whole organism. Such an assumption can, so far,
easily be ignored.
does that mean for our problem? It would seem like the brain has a
way of getting the information about one eye from one hemisphere, and
combine it with the information from the other eye and
The problem is that it concerns the same kind of
information in both hemispheres. No cueing would seem necessary.
Also, even if one hemisphere could cue the other, not all eye
movements, and certainly not torsional eye rotations, are under
voluntary control. Furthermore, the cueing language would have to be
very sophisticated to relay the need of rotating the eye around its
axis until it fits the other image.
All in all, inter-hemispheral
communication does not sound like a viable option.
last remark: Gazzaniga
often made the patients sit on their hands, or restrained their body
movements because he considered the attempts of communicating one
hemisphere with the other as a form of "kids cheating in a
classroom". He was so convinced of his model, independent
modules cueing each other, that he never stood still by the
possibility that it was in fact one and the same mind that was trying
to solve the problem as best as it could.
stories relayed by the splitbrain tradition would certainly seem to
favor the parallel view. The image of a patient trying to put his
pants on while his other hand tries to take it off is a soap series
worthy. Still, I would bet that even such a tragicomedy was in fact
built out of two independent blocks: the hands, I surmise, were not
working against each other at the same time, but alternately, however
fast the change from one hemisphere to the other went. If I am right,
that would mean that the same mind was indeed behind both series of
actions, but each time following different experiential
Applied to binocular disparity, and the ubiquity of
ocular dominance [King and Zhou "New Ideas About Binocular
Coordination of Eye Movements: Is There a Chameleon in the Primate
Family Tree?", 2000] I would say that we always see mainly
through one eye. What the other eye, when it is open, adds to our
vision is not fused with what we are already seeing, but added to
How can you blend images together? Fusion is something I would
not know how to explain, neither in neuronal nor in supra-physical
What I can understand is the fact that we see not
only what both eyes see, but then through the dominant or fixating
eye, plus what each eye sees but the other does not.
but not least: Wheatstone
stereoscope was aimed at foveal vision, the area which was declared
free from binocular disparity by Panum, Nagel and others. Wheatstone
has been neutralized, his invention taken as a gadget, but its
theoretical implications ignored.
contradiction remains. You cannot have a working stereoscope and a
disparity free fovea. One of them has to go.
the contradiction between a working stereoscope and a disparity free
fovea it is only active as long as we consider binocular disparity as
the cause of depth perception. Once we accept that it is only one of
the ways the brain has to experience 3D, the principle that
corresponding points in the retinas make binocular single vision
possible can also be accepted as another empirical rule. Just like
viewing two plane images gives a depth impression. We do not need to
explain those principles, just acknowledge them and study their
doing that we avoid at the same time the fallacy of the neural
applied to the case where both retinas get a different input, we can
take inspiration of the split-brain paradigm.
fast alternating fixation: the brain tries to fixate with each eye
independently of the other.
ocular dominance: it settles on one view.
if normal conjugate fixation is artificially made impossible.
far as the controversy between Helmholz and Hering concerning common
or differentiated innervation of both eyes, I think that both
were right in some respects, and wrong in others. A discussion for
Cyclorotations: do they really exist?
are of course mechanically possible [I am so glad I do not have to
say "metaphysically possible" for once!], but the only time
I have seen them were in computer animations on the web. None of the
videos I have watched concerning eye movements has ever shown an
actual cyclorotation. So I will admit that I am a bit at a loss
is another reason why I do not believe in the reality of
looking at an a somewhat inclined vertical that suddenly moves to a
sharper angle. The line will impinge on different photoreceptors of
the retina. Cyclorotations are supposed to prevent that.
should they? We see an object in one position, then in another. The
idea that we would not know that it was still the same object, the
so-called correspondence problem, does not really make much sense.
When we are looking at an object, we are not only using our eyes or
isolated areas of our brain. The whole brain is engaged. That is also
what makes smooth pursuit possible. Nobody ever wonders how that is
possible in the context of the correspondence problem, even though
both deal with the same so-called problem: the same object on
different locations in space and on the retina.
assumption that a single object has to leave an impression on
corresponding parts of the retina was infirmed by the stereoscope.
So, unless we want to attribute to the brain the faculty of
distinguishing the cases of binocular disparity which should be
respected, because they create a 3D image, from those where the
disparity creates a double image, then we have to accept the fact
that the brain has no control on any of these situations.
if it did, how come we still see double images where there are single
to the horopter? Which version?
and eye movements
concept of cyclorotation was deemed indispensable with the discovery
that the after image on the retina changed position with the
movements of the eye. Helmholtz gave even an example of when the
after-image rotated, and when it did not. Nowadays afterimages are
not used anymore to study eye movements because they are subjective
sensations that the researchers in the 19th century tried to elevate
to scientific data. Magnetic and electric devices are used instead,
like the so-called search coils. I honestly do not know the technical
details, but apparently their results are fully compatible with those
given on the basis of after-images. That is why I will consider them
as similar and hope that I am not wrong.
are persistent visual stimulations which do not need fixation to be
perceived, even if they were born in the foveal area. When we move
our eyes intending to fixate our gaze on another object, the
after-images remains imprinted on the same location on the retina
where it originally came to life. Seeing them rotate is then the only
reason why the German physiologists [Panum was Danish and Donders was
Dutch] came to believe in cyclorotations.
cannot fixate on an after-image, for the simple reason that the eye
cannot fixate on the retina itself! The fact that the after-images
has rotated in its new position, relative to the original one, does
not mean necessarily that our eye has rotated around its axis. That
is only the case if you take the after-image as starting point.
would mean fixating the after-image before, during and after the eye
has finished its movement. But that is of course impossible.
the eye movement is unrelated to the after-image then the rotation of
the after-image must therefore have another
not necessarily mechanical. After all, we are speaking of a visual
what about a retinal image? Can it be said to rotate around it own
axis as the after-image is supposed to do?
such a retinal image could be compared to a drawing on or inside a
globe. How could it ever rotate around its own axis?