Esiste una reale differenza tra l'emisfero destro e l'emisfero sinistro?
Questo è il grande tema di cui Liam Keating tratta in "Associative and oppositional thinking", articolo che ha scritto per Dialogues in Philosophy, Mental and Neuro Sciences che uscirà in versione ridotta per la stessa rivista a dicembre 2017.
Questo è il grande tema di cui Liam Keating tratta in "Associative and oppositional thinking", articolo che ha scritto per Dialogues in Philosophy, Mental and Neuro Sciences che uscirà in versione ridotta per la stessa rivista a dicembre 2017.
Ho scelto di condividere l'articolo nella sua forma integrale perché penso possa essere un interessante spunto di riflessione sul binding problem, ossia il problema di come sia possibile "collegare" o integrare l'attività di gruppi neuronali.
Ne approfitto per ringraziare Liam Keating per la sua disponibilità.
ASSOCIATIVE
AND OPPOSITIONAL THINKING:
THE
DIFFERENCE BETWEEN THE BRAIN HEMISPHERES
Author:
Liam Keating
Abstract
Concepts
need to be separated from each other in the brain in order for an animal to act
on one object in isolation. A possible solution is to inhibit common feature
neurons that are shared by concepts. One problem with doing so is that each
feature of every concept is a commonality with some other concept. This can be
circumvented if common features are only temporarily inhibited while two
concepts are both active at the same time. The difficulty can also be resolved
if the brain is divided into associative and differential or oppositional areas
which operate concurrently. Associative thinking, proposed to be the sole
mechanism in the right hemisphere, produces poorly defined but well related
concepts. Oppositional thinking, speculated in the left hemisphere, cancels out
the common features of concepts to expose the differences, resulting in clear
definition of the concepts, allowing more accurate targeting of real objects
for action upon them. This paper discusses how the proposed operational
differences could cause the behavioural differences that have been found in the
two brain hemispheres. The theory also has implications to how concepts can be
defined mechanically in the brain.
Keywords
Conceptual
thinking, Cognition, Binding problem, Lateralisation of the brain, Object
manipulation, Spatial perception, Language, Abstraction.
Introduction
What is commonly known in
neuroscience as the ‘binding problem’ could more accurately be called the
‘separation problem’. The question has generally been viewed as a problem of
how the brain can divide the world into concepts by binding the correct feature
neurons together to form each object concept. However, an associative brain
that works by strengthening cell connections should have no difficulty in binding
feature neurons to form a concept. The feature cells are potentially any cells
that are activated by sensing of a colour, shape, sound, smell or other
sensation. When active at the same time, it is thought that feature neurons reinfo rce synapses from other active neurons so that
they become reminders for each other in future – a network memory or concept.
The problem is that all the feature
cells that are active at a given time would reinfo rce
together, joining everything that is currently being sensed and memorised to
each other. Also, because an object will have some features in common with
other objects, these common feature neurons will join concepts of objects that
were seen at different times. Therefore in a purely associative brain all the
sensory neurons would form a single concept of all that has ever been
experienced and all the motor neurons would form one habit or very confused
skill.
To some extent objects can be
segregated by their independent movement and separability from other objects. Vision
is differentiated by tactile knowledge and vice versa. Also motivations,
desires and fears that target specific features, can provide top-down
definition of the world by limiting an object to its features of interest.
Furthermore, the overlay of features in a single location, for instance a shape
and colour in the same retinal area, can correctly be bound together in the
retinotopic or somatotopic regions of the cortex and these regions might
coordinate binding of the same features in non-locational, non-'topic cortex
areas.
However there remains a difficulty
of how two object concepts that contain a common feature neuron can be
separated. The common cell will bridge the boundary and a desire or fear
complex will not be able to distinguish which feature neurons form the concept
that contains the features of interest and which neurons are only an object
associated with a wanted container object. In other words, without some way to
segregate the concepts, the motive to eat (or avoid) will drift from the
object, that contains the desired sensory features, to the associated object,
as long as they both contain some of the same features. The animal will eat the
wavy looking meat and the wavy looking soil, the red meat and the red flowers
it is near to. It would not be able to segregate the desired from the
undesirable in its memory, therefore nor in its action targetting.
This
paper presents a theory to explain the different behaviours of the brain
hemispheres. The mechanism that is speculated to operate in the left hemisphere
can also explain how the world is sliced up to form isolatable object concepts.
In brief the idea is that in the left hemisphere any common feature neurons
shared by two active concepts are inhibited so that the shared features cannot
bind the two concepts.
For completeness I want to add that
there is a separate question that can rightly be called a binding problem. That
is, how can you know that a blue patch or circle seen by cells on one part of
the retina is the same as a blue patch or circle seen by cells in a different
retinal region? Or how can you know that a pin-prick or warm touch to the
shoulder is the same quality as a pin-prick or warm touch to the foot? The
simplest solution would be for each of the retinotopic and somatotopic neurons
that register an identical feature to be connected to a hub neuron. The hub
neurons, with connections between each other, could form non-locational
concepts. This is explained slightly more elsewhere.
Brain
hemisphere behaviours
The right hemisphere (and left
hand) holds an object steady, the left hemisphere (and right hand) operates the
tool. The right hemisphere seems to memorise relationships between objects
while the left memorises components within objects. This is suggested by how
the right hemisphere of split brain patients can draw a simplified house with
no detail whereas the left can draw the parts in detail - roof, chimney,
windows etc - but in the wrong places (Gazzaniga, 1967; Lamb
and Robertson,
1991; Bogen 1969). The right hemisphere is more proficient at map reading and
other spatial tasks. The left deals with most speech and language but struggles
to recognise or speak connecting words such as 'be' 'and' 'or' 'of' (Lehrer,
2012). The right can understand language, including previously unheard
metaphors, but seems unable to speak most words (Altmann
et al, 2012). The left hemisphere has been generally found to be the impulsive,
incautious side, whereas the right tends to be involved with retreat or wait
behaviour (Carmel
The right hemisphere might not be
able to recognise boundaries. Jill Bolte Taylor, a neuroscientist, gave a TED
Talk about her experience during a stroke that affected the left side of her
brain. For some phases while she sought help she said that she could not dial a
phone number and presumably only her right hemisphere was operating then. At
these times she looked at her arm and at the wall behind and said that she
could not conceptualise where her arm began and the wall ended (Taylor
It is difficult to discern a common
thread in these hemispheric differences. Overall it seems that the left
hemisphere isolates objects to act on them whereas the right hemisphere
connects things to see wider relationships, allowing it to recognise wider
consequences and allowing it to hold an object steady in relation to other
things.
Proposed
mechanisms
How can the left brain isolate and
distinguish two object concepts? When two different but similar concepts are
live in the brain at the same time, any feature cell that they share will be
over-active compared with the other feature cells. This is because the shared
feature is powered by the sources of both of the live concepts that it is a
part of. The concepts may be live because one concept is being searched for and
the other is seen in reality, or because they are both being searched for and
therefore presumably energised by subcortical motivation/search structures.
In any case, if the second live
concept is different from the primary concept that is wanted and the two
concepts share one feature, then this over-active feature cell would reinforce
strongly to the other feature cells of both concepts. The common feature cell
will act as a link that activates both concept networks in future, whenever one
concept is active.
As
a simplified example, imagine a young scavenger animal that has experienced meat
and found it satisfying but so far only differentiates it by its redness, as it
has seen meat of many shapes and textures but always red. Then it eats some
liver from a carcass. Let's assume that the new taste wakens an avoidance
instinct (see note 1 at the end) that deems it a poison. The animal cannot
differentiate liver by its colour which it shares with meat but the different
visual texture can distinguish the two - smooth appearance of liver versus
fibrous or wavy meat appearance. The animal licks and checks the visual
appearance of one part and concentrates to reiterate the signal and reinforce
the association between liver taste and smooth visual texture. Then it does the
same to further memorise meat and its now more limited visual texture range.
However, the association between
red and meat and red and liver taste will also be strengthened with each
iteration. To discern and to memorise liver and meat as two concepts when they
are both in view, to treat them differently, the brain must inhibit activity of
the link cell, the 'red' cell (see note 2).
It
cannot do this simply by inhibiting whichever is the most active cell as the
shared feature cell will not necessarily be the most activated compared with
other prominent feature cells. However, the shared cell will activate more
strongly than usual when two concepts that include it are both active and this
would allow the common cell to be identified.
The
searching instinct or subcortical complex cannot trial to find the unusually
active feature cell by turning off one concept at a time, since a comparison
cannot take place while the wanted concept is inactive.
Therefore,
does the brain distinguish the anomalously energetic feature cell by
measurement of feedback? Does it measure its supply of power to the feature
cells of the wanted concept and then measure and compare the returning signal
from each of those cells? A type of radar in the brain? It could then
distinguish if one feature feeds back more than it was supplied and must
therefore be shared by another live concept.
A
concept set of features is lit up when it is searched for. A different object
may be found in reality that has one feature in common with the wanted concept.
The searching complex supplies energy and measures feedback from the wanted
feature cells and one cell returns more power than all the others. The left
hemisphere inhibits this cell. The inhibition of disproportionately elevated
feedback in the left brain will split two active concepts where they share a
common feature. This could explain many of the differences in behaviour of the
brain hemispheres, as described further on.
When
a fully matching object is found in reality, the wanted concept cells will all
feed back more energy than they were supplied. No cells will be disproportionately
active and the uniformly increased signal from all wanted feature cells
registers the discovery of the wanted thing, by switching the brain to approach
behaviour.
Sometimes an animal will need the
left brain to expand its associations to an object. For example if food is
always found next to a tree trunk, then the food-trunk association would help
in future searches. Therefore perhaps the inhibitory mechanism only operates
when the subcortex is actually enervating a concept, searching and testing it
against things in reality. When not actively searching, memories can form in
the normal associative way, in proportion to real encountering.
***
Let's assume the same type of
concept-commonality highlight mechanism serves the right hemisphere, except
that when a cell feeds back too brightly it is energised more instead of being
inhibited, to strongly reinforce its connections to other active cells. The
shared feature in the right hemisphere therefore becomes the main feature of
the relationship between the two partly similar objects.
The difference then is that the
right hemisphere will tend to shift focus towards wider and larger
relationships, category memberships with few commonalities, whereas the left
will tend to focus on components. This happens in the left brain because when
doing almost anything with an object, you have to focus on it one part at a
time. Since for the parts, the whole is a commonality, the whole disappears to
the left brain. This inhibition will apply to visual cortex cells that are
activated by the sight of lines or edges at the boundaries of two things and
also to the complex shape cells that register the shape of the whole.
This can explain why the left brain
can copy parts of a drawing but fail to draw how they relate as a whole. It can
also explain why the left is poor at map reading and other types of spatial
cognition, as it inhibits the link between adjacent components whenever
concentrating on one. The right brain simplifies by concentrating on the common
junctions between parts of a drawing, therefore conversely mainly ignoring the
details.
***
The face recognition centre is
typically on the right side in the human brain, in right-handed individuals. If
the theory postulated here is correct then the right hemisphere should be no
better at discernment and perhaps worse than the left. The left brain will
distinguish faces by their internal relationships and compare one face to other
faces by cancelling out similarities, to narrow down the distinguishing
features of a specific face.
The right brain will distinguish
weakly by internal facial features as it has no mechanism to differentiate
while two faces are live in the mind. However, the features of a single face on
its own in reality will reinforce to many other memories that involved that
person. The whole persona will be recognised so the visual feature cells will
also be somewhat distinguished by reinforcing strongly to the contextual
memories. Individuality, a strong idea, in the right hemisphere is not
difference but breadth and strength of links to other memories. Facial
individuality will form there because one face is associated to one set of
memories, a different face to a different set.
However, commonalities between
faces will cause the right brain to expect common behaviour. This will make the
right-hemisphere better at reacting to expressions than faces. It can still
work well enough for face recognition because the more memories a person is
associated with, the more highlighted and therefore differentiated are their
facial features.
The reason the right hemisphere has
difficulty speaking may be because it connects words to their opposites. In the
right brain everything will mean everything else to some extent. Opposites such
as the concepts of 'man’ and ‘woman’ have more similarities than differences.
Each word is slightly more connected to its respective real gender group but
both words will also be cross-connected in the right hemisphere by their
commonalities - both words mean human, adult, hairy in some places etc. The
feature networks of both words - sound or visual letter features - reinforce to
both gender concepts so the word definition is poor. Such definition becomes
strengthened, the dent of a word and meaning association is deepened, by
regularity of the word being used while one gender is present in mind. With
strongly associated words the right brain could still not exclude other words
but could guess with some confidence and could possibly learn to speak by this
means.
When the right hemisphere is asked
to specify a word for something, many related words will come to mind including
contextual opposites and category options which would include some
inappropriate words from higher categories. The right brain will find it
difficult to choose. However, when the right brain is spoken to, the words will
connect to their respective concepts more than to others, so meanings can be
grasped. Also the words of a sentence that have been heard will affect
connectivity of each other's concepts, so the sentence altogether supports a
possible meaning with sufficient confidence for the right brain to believe that
it understands what was said to it.
***
To sum up, lone-highlight
inhibition in the left hemisphere will result in division by commonality and
therefore to see the thing that is focused on as an isolated object. In the
right hemisphere reinforcement of an anomalously active cell will allow a
concept to be related to others that share that feature.
This happens when the brain
searches for an object in reality by energising the concept it wants. If a
common quality is seen in a different real object, the left hemisphere will
note the difference, the right hemisphere will
be tempted by the similarity.
Also it happens when searching for
a commonality and not a specific object, for example when looking for anything
sweet or anything that can act as a screwdriver. Then the right brain comes
into its own.
Further
considerations and questions
Concurrently
experienced objects versus timeless commonalities
If two objects are present in the
same place and time, all feature cells of both objects can associate to all
others. This is labelled here as a concurrent association (CA).
If two objects are not experienced
together at the same time, only the features that they share will link the two
network concepts. This type of concept relationship is called here a timeless
associate (TLA).
When the brain searches or thinks,
I assume that it intensifies the signal through whatever concepts it wants to
find or think about. The signal will pass from the activated concept to the
feature cells of its CA's ‘all to all’. Each of the wanted concept’s feature
cells will also be associated to other concepts with a category link, one
common feature, the TLA's.
Presumably the brain or subcortex
only knows it has found an answer by feedback from the quest concept itself.
When thinking, there is no second concept lit by reality, so the only feedback
will come from loops where the signal has passed through to an associated
concept network and back again to the activated feature cells that supplied the
loop.
If a CA loops back, the activity of
all the features of the wanted concept will be increased equally so the left
brain will not inhibit the CA. However if a TLA receives activation through a
single shared feature, and the signal loops and returns rather than
dissipating, then that feature will stand out. The left hemisphere, while in
search/anticipation/thought mode, will detect the anomalous high feedback and
inhibit the overactive feature cell that is feeding the TLA.
The left will remember things that
were actually seen together. It would have no access to memories of all the
objects that share one or a few features with a wanted concept. Category
knowledge will only partially and accidentally form in the left brain because
of being told, within a few seconds, that pineapples and tomatoes are both
fruit, or that sunsets are similar to tomatoes in colour, or if at some time
tomatoes were actually looked at (while in idle mode) during a sunset.
If asked "What is the capital
of France?" the left hemisphere enervates all features of both concepts.
The signal passes through many concepts that were heard or otherwise
experienced together with 'capital' and 'France' in the past. The 'Paris'
concept feeds back without anomaly as a CA to both question concepts, returning
power to all the feature cells of both, because it has been experienced with
both many times. This evenly increased feedback registers as a match and causes
the left brain to trigger speech.
How can looping cause the signal to
increase and produce feedback, rather than to dissipate? Does there have to be
some mechanism, perhaps a specific neurotransmitter released while in
anticipation/thinking mode, that encourages cells to reach action potentials
when receiving weaker inputs than usual?
Anomaly
ratio
The signal ratio of
[anomalies]-versus-[all feature cells] that triggers the inhibition mechanism
must be small so that if enough anomalies are registering, the object can be
recognised as a match that is partly hidden or viewed from a new angle. Also, a
concept is not a set of pinpoints in feature ranges but is whole sections of
each range. For example meat can be various textures and colour shades. A real
sample of meat will only activate short sections of the remembered concept ranges,
so the trigger anomaly ratio has to be very small.
Either that, or the whole concept
ranges are at first searched for, then when a piece of meat is found, the
smaller, visually active feature range sections are focused on, then the
anomaly mechanism operates.
Abstractions
in left and right
In the right hemisphere, all is
abstraction, every object is made of features that relate it to other objects
that have one of those features. In other words, all is abstract categories in
which tomato and sunset can be classified together just for both being red,
even if never seen together.
In the left hemisphere, operations
can be abstracted. For example, if the left brain is told that "A is
taller than B and B is taller than C" and then asked "Is C taller than
A?" it will inhibit 'tallness'. This is because each object has tallness
as a common feature. Except for the nouns, the words that remain are 'is ____er
than'. Individually these two words and suffix are likely to be difficult for
the left brain to understand, since they have no opposites against which to
form boundaries, no negatives to define them except by adding the word ‘not’.
Altogether they represent a common correct grammar and they mean 'more',
signified by the '____er'. The 'is' and 'than' signify the direction.
This is a left brain type of
abstraction. A descriptive operation without a description, it is replaced by a
silent generalisation of all adjectives that act with grammar the same way.
In a real comparison of tallness,
when a subject is asked to say which of two lines on a page is taller,
'tallness' cannot be inhibited. The other features of the two lines will be
inhibited in the left hemisphere. The concepts of 'tallness' and 'most' have to
be assisted (by an assumed subcortex module) since they are the search
concepts, so the two lines become two simple features, vertical lines in two
spatial locations.
How tallness of the lines is
actually compared is unknown, perhaps achieved by linking to old memories of
making such comparisons and the valuing of the 'most' that they contain, by the
memory of some type of reward. Or perhaps by taking advantage of the graduated
nature of each feature cell range, by measuring the signal strength from one
end of a feature range and comparing the signal that is produced when looking
at each of the two lines. In this instance the compared signal would be from
the 'tall' end of a range of visual cells that are activated by different
vertical lengths.
Motives
determine the focal point
Desire or fear determines what is
an object - that contains an instinctive, pre-wired cue-set of features - and
what is an associate or background. Clearly, or unclearly, an instinctive
cue-set is contained in the object but also within the environment or
background that contains the object. In the left hemisphere the desire or fear
draws limits, for example where a desired taste is found to geographically
overlap with a visual feature, this appearance is meat taste, all else is cut
off from the concept due to either lacking commonalities or having too few. In
the left brain desires and fears cut reality into pieces. In the right brain a
desire or fear is more like a hammer, it creates a definite centre - a
pre-wired feature cell network - but with an indefinite surround of
associations, that are weaker and weaker at greater distance from the central
instinctive concept.
Possible
mechanisms
No doubt there are many possible
architectures for the match/commonality/non-match mechanism postulated here and
it is not the aim of this paper to specify the probable architecture. The
mechanism would need to include a method to record the signal strength issued
to a feature cell (or feature cell range) and then to somehow compare the
return signal against what was supplied. Perhaps the recording is achieved
simply by activating a chain of cells at one end such that the stronger the
signal, the further it progresses along the chain. The return signal then has
to be tested on the same chain as the supply signal for a comparison. The
results from different feature cells would have to be collated, with different
decision routes depending on the proportion of feature cells that feed back
excessively.
Concluding
comments
The mechanism proposed here can
explain many of the reported behaviours of the left and right hemispheres.
Questioning of subjects with right hemisphere damage shows that the left brain
performs poorly in understanding incongruent adjectives in sentence pairs, such
as 'John is taller than Bill. Who is shorter?' (Caramazza
et al, 1976). This is explainable because the main definer and therefore
regularly inhibited partner of 'tall' in the left brain is 'short'. As the
silent partner, unreinforced at the commonality, the opposite word cannot be
accessed while thinking except by a circuitous route.
The theory can account for why the
left tends towards the obvious, the things previously encountered together in
reality or speech at the same time, while the right tends towards rare
commonality, higher category, timeless associations (Beeman et al, 1994; Burgess
and Simpson,
1988).
The right is subtle and the left is
precise. The right is dense but vague, the left is definite although something
is always neglected. In the right hemisphere the visual edge/line cells at the
boundary between Jill Bolte Taylor's arm and the wall behind joined them as one
concept, while Jill was suffering a stroke. In the active left hemisphere the
edge/line cells are the inhibited commonality, the division of adjacent
things.
Both hemispheres have full concepts
formed by experience of many examples of dogs or towns or of a particular face.
In both hemispheres associations form between concepts that regularly occur
together. Both hemispheres can distil a person to their component organs and
atoms. There would have to be a motive to cause such distilling. The left
hemisphere would see the organ in the person. The right hemisphere would see
the person as one of many with such an organ.
To communicate, the right
hemisphere points, and it may be trying to indicate the whole landscape, the
forest in the middle, or just one tree. The left hemisphere has to gesticulate
to exclude what it does not mean, and so it invents oppositional language. Most
concepts and words are defined both associatively and oppositionally, for
example 'apple' is associated to many examples of apples you have had and is
also defined oppositionally by everything that is not an apple. It is poorly
defined against jetskis and carpets, more precisely defined in opposition to
peaches and pears.
Existence and consciousness are
examples of concepts that are mainly defined associatively. Their closest
opposites are non-existence and unconsciousness, which are too absolutely
different from the positive concepts to add much definition. In any case these
opposite concepts cannot be experienced. The concepts 'existence' and
'consciousness' associate to all experienced or thought of things, so even
associatively the two concepts can have little definition.
One prediction of the theory set
out here is that the left hemisphere should have difficulty with the concepts
of 'consciousness' and 'existence', in the same way that it apparently has
difficulties with shorter words that cannot be defined oppositionally. The
prediction is weakened since the left brain might have an oppositional
understanding of consciousness, by the third person view of other people
sleeping or awake. It is hard to see how the theory might become firmly
established other than if a suitable mechanism is found. However the brain must
do something like this.
Note
1
An instinct is envisaged as a
sensory trigger that when activated connects on to an action or search
procedure. For hunger the trigger is sensors in stomach and blood. For most
instincts the trigger is a pre-wired fear image such as a pigeon's fear of a hawk,
or a desire image or tactile concept, for instance to direct newborn suckling
or adult mating.
Note
2
Colour is coded initially in the
visual cortex as patterns of activation across small lumps of many cells known
as ‘colour blobs’, that are each activated by small patches of retinal cone
cells. However, it would be more useful for colour to be represented by single
cells on a spectrum, each activated most by a specific pattern of activity in a
colour blob. This may be the case further forward into the cortex. Single cell
registers would allow less complicated memory formation with other feature
cells than if using colour blobs.
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