Minds and Computers : An Introduction to the Philosophy of Artificial Intelligence
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is the disposition to (inter alia) engage in food-seeking behaviour,
then I have learned nothing. The final objection to behaviourism takes the form of an internal critique: we show that behaviourism fails by its own lights. Behaviourism is a reductive theory. The whole point of the theory is to take talk of mental states and replace it, in careful analyses, with theoretical terms which satisfy positivist criteria of observability and public verifiability. The aim is to eliminate reference to mental states entirely by reducing talk of mental states to talk of dispositions to behave. Behaviourist paraphrases of mental state terms, however, turn out to contain ineliminable reference to the mental. To say that Tillie clutches her jaw is to say more than just that her arm raises in a jaw- ward direction. To say that she seeks a dentist is to say more than just that she is impelled dentist-ward. Rather, the attributions of ‘clutch- ing’ and ‘seeking’ are agentive attributions. To say these things is to say that Tillie actively, agentively and intentionally clutches, seeks and so on. This is already a mental attribution. Human behaviour is always already a mental phenomenon. It is impossible to enumerate convincing dispositional paraphrases for mental terms which do not make reference to just such agentive verbs as ‘clutching’, ‘seeking’, ‘organising’, ‘ensuring’, ‘attending’ and so on. As such, talk of the mental is ineliminable and the behaviourist has failed to analyse the ghost out of the machine. 26 C H A P T E R 4 NEUROANATOMY We’re now going to take a brief diversion from our examination of philosophical theories of mind and develop a rudimentary under- standing of functional neuroanatomy. The introduction to neuroanatomy here is going to be very cursory indeed. My aims in this chapter are quite modest. In the first instance, I want to show how parts of the brain are specialised for processing certain functions. In particular, we will see that our linguistic capacity is strongly localised and subserved by a rather extraordinary neuro- biological adaptation. In the second instance, I want to give a basic understanding of the operations of neurons. This will serve us well much later in the book when we examine artificial neural networks. Overall, I want to give a sense of just what an amazing and startlingly complex object the human brain is. We’ll begin by describing macro-neuroanatomy – the parts of the brain which can be seen with the naked eye – and then move on to describe some basic micro-neuroanatomy. 4.1 MACRO-NEUROANATOMY The human central nervous system can be broadly divided into three areas. The spinal cord, the brain stem and the rest of the brain, includ- ing the cerebral hemispheres which constitute the cerebrum. The spinal cord (medulla spinalis) is of least interest to us. It carries signals between the brain proper and the organs and muscles. Continuous with the top of the spinal cord is the brain stem which can also be divided into three parts. The lower brain stem, or hindbrain, contains the pons, the medulla oblongata and the cerebellum (not to be confused with the cerebrum). The medulla is known to be implicated in the regulation of heart func- tion and respiration. The pons (bridge) mostly relays information 27 between the cerebral hemispheres and the cerebellum, but is also implicated in regulating vestibular function (balance). The human cerebellum (little brain) is highly distinctive. It is very densely packed with neurons – much more so than the rest of the brain – and quite regular in organisation for a neural structure of its size. The cerebellum is readily recognisable by the very fine folding of its surface, which allows for more surface area and gives it a distinc- tive wrinkly appearance. The human cerebellum is unique among mammalian brains in its complexity and intricacy of folding. The cerebellum is connected to most primary sensory processing areas and most motor neurons and is known to be implicated in the automatic governing of fine motor control. When, for instance, you learn to type without thinking about it, or to operate a motor vehicle without thinking about it, your cerebellum has been programmed for the execution of a sequence of fine-grained motor responses to various sensory inputs. The next part of the brain stem is the midbrain. The midbrain con- nects the pons to the upper brain stem. It is known to be implicated in secondary processing involved with vision and audition. It also contains the substantia nigra which stimulate production of the neu- rotransmitter dopamine and which play a role in assisting fine motor control. Parkinson’s disease, whose su fferers experience uncontrol- lable fine tremors, is a degenerative condition of the substantia nigra. The final part of the brain stem – the upper brain stem – contains the thalamus and the hypothalamus, as well as the pineal gland and the pituitary gland. The thalamus, which is continuous with the midbrain, 28 Download 1.05 Mb. Do'stlaringiz bilan baham: |
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