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One potential solution to the 'Humpty Dumpty Dilemma' is that the mind, somewhat mysteriously, emerges from the brain. In this line of reasoning, consciousness, as an emergent feature of the brain, extends beyond, or is 'more than the sum of the parts' of the brain. And since the mind transcends the brain, while the brain my be divisible, consciousness can nonetheless emerge unified from the brain — like the eye that emerges from the top of the pyramid on a dollar bill. (124)
... although the fundamental entities of the world and their properties are material, when material processes reach a certain level of complexity, genuinely novel and unpredictable properties emerge, and that this process of emergence is cumulative, generating a hierarchy of increasingly more complex novel properties. Thus emergentism presents the world not only as an evolutionary process but also as a layered structure — a hierarchically organized system of levels of properties, each level emergent from and dependent on the one below (Kim, 1992)
If consciousness were emergent2, then consciousness could cause things that could not be explained by the causal behavior of the neurons. The naïve idea here is that consciousness gets squirted out by the behavior of the neurons in the brain, but once it has been squirted out, then it has a life of its own (Searle, 1992) (qt. 126)
The notion that causal powers might exhibit radical kind emergence merits special attention since it poses perhaps the greatest threat to physicalism. If wholes or systems could have causal powers that were radically emergent from the powers of their parts in the sense that those system-level powers were not determined by the laws governing the powers of their parts, then that would seem to imply the existence of powers that could override or violate the laws governing the powers of the parts, i.e. genuine cases of what is called 'downward causation' . . . in which the macro powers of the whole 'reach down' and alter the course of events at the micro level from what they would be if determined entirely by the properties and laws at the lower level (Van Guilick, 2001, [this volume], p. 18-19) (qt. 126)
consciousness has proved to be particularly resistant to a simple scientific reduction to the brain. If consciousness can be shown to be in fact be a radically emergent feature of the brain, this could in principle account for a failure, on the basis of neurological principles, to reduce consciousness to the brain. And this in turn would force one to endorse a form of dualism. (128)
Hierarchical biological systems operate via constraint. The individual cells of the human body constrain the microscopic organelles of the cell to perform sub-cellular metabolic processes, and the organs of the body in turn constrain these cells to perform functions such as secretion or muscular contraction. The entire body of the person constrains the individual organs to breathe, digest, and perform the macroscopic functions necessary for life. For example, the mitochondria, the organelles responsible for generating energy from oxygen via cellular respiration, are a microscopic part of the cell that along with other cells make up the tissues that eventually give rise to the lung. The mitochondria contribute to the emergence of the lung at a higher level of the hierarchy of the body. The lung, at a higher level on the hierarchy, displays emergent features not possessed by mitochondria, for example breathing. If the lung did not breathe, the body would not have oxygen, and if we did not have oxygen, the mitochondria would not be able to carry on cellular respiration. The mitochondria contribute to the emergence of the lung, and the lung in turn constrains the mitochondria. (129)
The operation of the higher levels of the hierarchy of the lung is clearly seen to be the result of the operation of the parts of the lung and their interactions. Therefore, it is not surprising or mysterious that the whole lung considered in its entirety can affect and constrain the individual cells and organelles within it. In contrast, in Sperry's view, the mind is an emergent2 or radically emergent feature of the brain. Thus although the mind emerges from the brain, and is not reducible to the brain, it can nonetheless cause material events to happen in the brain. In this way, Sperry suggested that '. . . subjective properties were seen to exert control over the biophysical and chemical activities at subordinate levels' (Sperry, 1977), and the immaterial mind possesses causal properties over the material brain and constrains it.The causal power attributed to the subjective properties is nothing mystical. It is seen to reside in the hierarchical organization of the nervous system combined with the universal power of any whole over its parts. Any system that coheres as a whole, acting, reacting, and interacting as a unit, has systemic organizational properties of the system as a whole that determine its behavior as an entity, and control thereby at the same time the course and fate of its components. The whole has properties as a system that are not reducible to the properties of the parts, and the properties at higher levels exert causal control over those at lower levels. In the case of brain function, the conscious properties of high-order brain activity determine the course of the neural events at lower levels. (Sperry, 1977; reprinted in Trevarthen, 1990, p.384) (qt. 129)
Each cell of the retina responds to a particular area of the visual world called its receptor field. The receptor field of each retinal cell is quite small, and the brain must build up whole and unified mental representations from these discrete points of contact with the world. (130)
a single neuron in the brain could respond to a line in the world if a line of adjacent firing cells — each responsive to an individual point of light — converged upon a single cortical cell further along the processing stream. The single cortical cell could 'add up' the points of light that each lower order cell had responded and in this fashion a single higher order cell could respond to a line. (130)
Hubel and Wiesel also found that multiple simple cortical cells converged upon other single higher order cells further along the processing stream to create what they called complex cortical cells, and complex cells in turn converged upon single neurons to create hypercomplex cells with increasingly specific and complex response properties. The model of Hubel and Wiesel is hierarchical in that simple cells lower or earlier in the neural processing chain create cells of ever increasing complexity higher up on the neural hierarchy. (130)
This hierarchical process ultimately produces advanced 'higher order' cells that possess amazingly specific response properties. For example, there are neurons in the inferior temporal cortex far 'down-stream' from the simple cells found early in primary visual region that respond preferentially to highly specific and complex stimuli such as hands or faces. Some of these neurons are even responsive to a frontal view of a face while others react best to a side view. Neurons of this type led to the notion of the 'grandmother' cell, a cell so specific that it fires only to the face of ones [sic] own grandmother (Barlow, 1995). While cells of that degree of specificity do not exist, it is in general true that the farther along a sensory processing stream that one looks, the more specific a cell's response characteristics become. (130-131)
However, in the process of creating higher order cells, the receptive fields of these cells increase in size. While a retinal cell early in the stream monitors a small and specific point in the visual field, a hypercomplex cell such as a face cell will react to a face that appears almost anywhere in the visual field. It follows that while the cells early in the visual stream with small receptive fields 'know' where each line of the face is, these early cells do not 'know' that a given line is part of a face. The face cells, on the other hand, 'know' there is a face, but due to the process of topical convergence, these cells don't know where the face is located in space. While it is true that cells of the brain project to successive levels in a hierarchical fashion in order to code for increasingly specific complex and abstract properties, the information coded by cells earlier in the process is not and cannot be lost in awareness.
cells comprising both the early and late stages of the visual processing stream must make a unique contribution to consciousness. (131)
Therefore, in contrast to Sperry's model, consciousness does not emerge at the 'top' of the visual hierarchy. Even though the brain seems to be creating 'pontifical neurons' at the 'top' of the visual hierarchy, the conscious mind is in reality 'spread out' across the activity of millions of neurons located in different regions and levels of the brain. A visual hierarchy exists, but many levels of the hierarchy make a contribution to conscious awareness. This is even truer when the brain must coordinate features of a stimulus from multiple sensory domains, such as an object having both visual and auditory features. When considering the perception of a honking red Corvette passing a brown barking dog, binding must occur in both visual and auditory centres that are located in even more widely distributed areas of the brain. The brain must bind the colour red and the honking horn to the car, and the colour brown and the barking to the dog it passes, and not the other way around. And both of these elements must be bound to each other within the overall perceptual field of awareness. (131-132)From the standpoint of emergence theory, the point is that there is no 'top' of the visual pyramid where visual awareness may be said to radically emerge. All levels of the visual system lower and higher, contribute to consciousness (132)
If you say to yourself 'I will now move my arm' and you do so, you will experience an 'inner I' as the source of that action. Suppose I, as your neurologist, search for the source of that 'will' somewhere in your brain. I will find that there is no central, integrated and unified physical locus that is the source of that action. Just as in the perceptual hierarchy that appears to lead to the 'grandmother cell' in the visual system, there is no singular 'top' of the motor hierarchy, no 'ghost in the machine' as Gilbert Ryle (1949) put it, that can serve as the source of our unified 'will'. (132)
It is clear that vast areas of the brain are involved in the complicated act of speech production, yet somehow when we 'will' to speak, the entire act is unified into a whole and coordinated behavior. But there is no unified region or hierarchical level in the brain that in and of itself constrains our actions and intentions. Therefore, there does not appear to be any material 'top' to either the perceptual or motor hierarchy. (133a)
A non-nested hierarchy has a pyramidal structure with a clear-cut top and bottom in which higher levels control the operation of lower levels. A classic example of a non-nested hierarchy is a military command in which a general at the top controls his lieutenants, who control their sergeants, and so on, down the chain of command until we finally reach the level of the individual troops. (133b)
The non-nested hierarchy that Sperry envisioned is considered non-nested because while the successive levels of the hierarchy interact, each level of the hierarchy is physically independent from all higher and lower levels. The various levels of a non-nested hierarchy are not composed of each other. (133bc)
We are physically composed of minute organelles that are hierarchically organized to create a human being. In the hierarchy of a living person, it is the complete person who sits at the top of the hierarchy, and that person is not separate from the parts of which he or she is composed. Individual elements of the body that make up the person simultaneously contribute to the life of that person. The 'parts' of the person in this way are nested within the totality of the human being. (133-134)
In the perception of a speeding red Corvette, the roof and trunk of the car are composed of tens of thousands of individual line segments. These individual line segments of the car's outline then are combined into longer segments that produce the car's overall shape and form. The lower order features, for instance, the exact position of a small line sequence in space, emerge in awareness as 'part of' something else, such as the outline of the car. A short line segment is 'bound' to a longer segment to create the outline of the car, just as a small patch of red is 'bound' to a larger red patch that is part of the door. The redness of the Corvette is 'bound' to its shape which is bound to its movement which is bound to the honking horn, until all representations are 'bound together' to create the entire image. The colour, shape and movement of the car are nested together within the image of the car and this image in turn is nested within the entire scene. (134)
Colour and shape are represented in awareness as a nested totality. We do not experience the colour of the car independently from the experience of its shape. On the other hand, the experience of the dog that the car passes is bound to the car within the entire visual experience, but is not tightly bound to the colour or shape of the car. The higher level or complex neurons that code for car and dog as entities make greater independent contributions to conscious awareness within the specific colour or shape of the car. (134d)
When we speak, it is the idea we wish to express, the purpose of our speaking, that sits at the highest level of the action hierarchy, and the degree of constraint and purpose distinguishes intentional from non-intentional telenomic behaviors. Beating hearts do not act purposefully; toolmakers do. And the greater the constraint over nested parts within a hierarchy, the greater a behavior is purposive and therefore conscious. (138b)
... By its very nature, the brain functions in a fashion that produces irreducibly personal mental states, and the failure of mental states to be completely reduced to neurological states is not based on any variety of radical emergence of the sort posited by Sperry and others. Rather, from the standpoint of neurology, the irreducibility of mental states to the brain, to what extent such irreducibility exists, depends solely on the inability to reduce the subjective to the objective. (143)
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