In the seventeenth century, French philosopher René Descartes argued that humans have an immaterial mind (also called “soul” or “self” or “spirit”) over and above the material brain. This position is known as mind-body dualism. The mind is the origin of thought (“the engine of reason”) as well as “the seat of the soul.” For Descartes, the mind causally interacts with the brain, although this interaction is difficult to explain. Modern dualists have not been successful either, and this problem has led many philosophers, psychologists, and cognitive scientists in general (such as neuroanatomists, neurochemists, artificial intelligence researchers, scientifically trained philosophers) to argue for materialism, the view that denies there is such an entity as “the mind” and claims that there is only one entity, the material brain. In The Engine of Reason, the Seat of the Soul, Paul M. Churchland holds this position, a position supported by studies on brain-damaged and brain-lesioned patients. For example, postmortem examinations of the brains of people who had Alzheimer’s disease reveal material plaques and tangles throughout the fine web of synaptic connections of the neurons of the brain that embodies all of one’s cognitive skills and capacities for recognition.
Moreover, Churchland is impressed with the tremendous advances in the neurosciences and in AI research that allows modeling of brain processes. Modeling enables cognitive scientists to represent brain function as massively parallel distributive processing (PDP) of recurrent neural nets that carry out vector-to-vector transformations or vector completions. This model (perhaps theory) of human cognitive brain processes will effect, Churchland claims, a revolution in understanding of the self, consciousness, all cognitive processes, science, art, and much else besides. His book is intended to convey the possibilities and excitement of this revolution.
Churchland’s book is divided into two parts. Part 1 describes the enormous anatomical complexity of the brain and links this complexity to artificial neural networks in computer modeling that imitate parts of the brain. Part 2 explores the consequences of this neuroscientific approach to cognition and soul and, in the process, delves into the nature of consciousness and shows how the new neuroscientific approach can be applied in many other domains besides the study of consciousness, such as science, philosophy, ethics, law, and medicine.
Churchland begins by describing the enormous structural capacity of the human brain to represent the world. For example, a standard television screen contains about 200,000 pixels, the tiny dotlike elements that are easily seen if one peers very closely at the screen. However, the human brain has approximately 100 billion nerve cells, or neurons, each of which can also take on a full range of activation levels (or “brightness values” when compared to pixels). Counting each neuron as a pixel, one can calculate that the brain’s representational capacity is about 500,000 times greater than a television screen’s representational capacity.
Churchland then asks the reader to consider one of the twin towers of the World Trade Center in New York City. Imagine the entire outside surface—all 500,000 square feet of the skyscraper—to be tiled with 500,000 television screens so that each seventeen-inch screen is glued next to each other and facing outward. Assuming there are about 200,000 pixels per square foot, one can calculate that there are 100 billion pixels in this setup that correspond to the 100 billion neurons in the human brain. This is the minimum visual representational power of the human brain, for the brain can also represent reality in many other dimensions, including, for example, social, moral, and emotional.
Churchland then asks the reader to picture that the skyscraper’s pixels are embedded in a thin sheet of aluminum foil that covers the entire...
(The entire section is 3,121 words.)