The Location of Consciousness
That different areas of the visual cortex respond to different stimuli and are arranged in a somewhat heirarchical manner has already been established. Neurons in the lower region of the cortex react most to simple pieces of a scene, with only some attention given to the broader context. Higher regions respond most to more complicated objects (hands, faces, etc.) with less attention given to where these objects appear in your sight. There is no current evidence for an area which is responsible for the global aspect of vision.
The challenge, then, is to determine which region of the brain controls the area of sight of which we are aware at any one moment. Theories exist that this section is located in either the high or middle region of the visual hierarchy. Philip Johnson-Laird's theory that this area is on the high end of the hierarchy contends that the determining region is responsible only for dealing with the processed information which it is given. In contrast, Ray Jackendoff contends that consciousness lies somewhere in the intermediate levels and results from population dynamics.
At first, these two theories may seem only subtly different and irrelevant as far as determining the actual location of consciousness. They, however, provide profoundly different ways of addressing the problem and, hence, of attempting to solve it. To illustrate, consider the mind as a an idealized courtroom. The lawyers are responsible for sorting and identifying all the evidence and then presenting it to the jury. The jury then must meet and discuss together the evidence which they have seen. They must decide which evidence to give the most weight and which to ignore. Based on the decision of the group as a whole, they present one verdict. The judge then decides the sentence, without having had any say in the verdict itself. Johnson-Laird asserts that consciousness lies in the judge, whereas Jackendoff thinks that it lies in the jury. The differences, as we shall see, are profound.
Johnson-Laird's judge determines the perceived area based on the information presented to it alone; it has no dealings with the processing which occured at the lower levels in the identification of objects. Other analogies for this theory include a conductor of an orchestra, unaware of the exact technique and posture of each individual member yet aware of the sound they produce, and the operating system of a computer, which allows communication between different programs and devices without itself being involved in the creation of the data.
Crick finds some fault in this theory since consciousness is hardly likely to be that exactly defined. Not only would consciousness more likely be spread out between different regions of the brain, but also, within the regions themselves, the decision would be spread out between various neurons.
Crick leans more towards Ray Jackendoff's theory which has much to do with David Marr's 2½D sketch. Jackendoff contends that conscious lies in the 2 1/2-D sketch and not in the 3D model, which would correspond to a higher level in the heirarchy. Like most of our thoughts, the 3D model remains outside of our consciousness yet influences heavily the final product of which we are conscious. Furthermore, Jackendoff claims that the processing of the 2 1/2-D sketch is determined by selection from a population of possible thoughts.
Despite making strong statements on where consciousness is most likely to be in an abstract sense, these theories remain almost purely psychological and do not address the actual characteristics of neurons which determine consciousness. In fact, no one actually knows where these consciousness determining neurons are located or what distinguishes them from other neurons.
These theories may provide some clues to aid in determining the identity of these neurons, though. Consciousness stems from awareness, so we should examine the behavior of neurons associated with objects of which we are aware. Furthermore, awareness arises from short term-memory, so we should try to better understand short-term memory. Difficulty arises when we consider that we are able to be aware of multiple objects at a time. The processes which determine our consciousness are anything but understood and seem to consist of some sort of temporary binding similar to that involved in the recognition of objects.
May 25, 1996.