Considering how a tree is represented in the nervous system brings us back to one ofthe defi nitions of mind presented in Chapter 1, which stated that the mind is a systemthat creates representations of the world, so we can act within it to achieve our goals.Applied to the brain, the major idea behind this statement is that a tree, and everythingelse we perceive, is represented in the brain. We can appreciate what this means by con-sidering what happens as we look at a tree.We see the tree because light refl ected from the tree enters the eye and an image of the treeis focused onto the retina, the layer of neurons that lines the back of the eye (● Figure 2.17).The important word here is image, because it is the image created by light refl ected by thetree that gets into the eye, not the tree itself. The idea of the tree not getting into the eye mayseem silly because it is so obvious, but the point is an important one: What enters the eye is arepresentation of the tree—something that stands for the tree.One property of this representation is that although it may look like the tree, it is alsodifferent from the tree. It is not only smaller, but may be distorted or blurred because ofthe optics of the eye. This difference between the actual tree and its representation becomesmore dramatic about a few thousandths of a seconds later when receptors in the retinatransform the tree’s image into electrical signals, which then travel through the retina, leavethe eye via the optic nerve, and eventually reach the primary visual receiving area of thebrain. Our perception of the tree is therefore based not on direct contact with the tree,but on the way the tree is represented by action potentials in the brain. Early research onthe nature of this representation led to the proposal that this representation could involveneurons called feature detectors that respond to features that make up objects.
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