When you learn a motor skill, such as walking, driving a car, or riding a bike, you first practice it over and over until you no longer need to think consciously about the individual steps. As the brain builds new networks of neurons, the movements needed to control the bike are stored in your procedural memory, becoming unconscious—as automatic as breathing or blinking. Although it begins to feel completely natural to ride a bike or drive a car, it can be difficult to explain the process to someone else. Because the movements are controlled unconsciously, it's much easier to physically do it than to talk about it!

Sense organs such as our eyes, ears, and skin detect information from the environment in the form of physical energy. This information is then sent to the brain as electrical impulses. Perception is the process of acquiring, interpreting, selecting, and organizing all this information. If your brain didn't have the ability to organize and interpret information picked up by your senses, the world would seem like a hodgepodge of random colors, sounds, smells, tastes, and touch sensations. Without perception, you couldn't do basic things like understand language or recognize faces.

The eye collects visual information from the world, but it's the brain that turns this information into the images we see. This process begins when light enters the eye through the cornea and the lens behind it. The cornea and the lens focus the light to produce an image on the retina in the back of the eye. In the retina, over a million neurons called photoreceptors turn the light into electrical signals. There are two types of photoreceptors: rods, which work in dim light, and cones, which are sensitive to black, white, colors, and details. Electrical signals pass from the photoreceptors to the optic nerve and to the optic chiasma. There, the optic nerves from both eyes cross, allowing signals from the left halves of each retina to combine and flow to the left hemisphere of the brain. The same thing happens on the right. This information is processed in the thalamus and then travels to the visual cortex, where the signals are processed to detect the shape, color, and movement of the image we see.

Certain body movements, such as clapping your hands or dancing, are voluntary — you consciously decide when to move the muscles involved with the activity. Other body movements, such as your heart beating or your lungs breathing, happen automatically. These kinds of actions are called involuntary. Often voluntary and involuntary actions support the same goal. To steer clear of an oncoming rider, a cyclist makes the voluntary action of moving her handlebars. This conscious decision takes place in the brain, part of the central nervous system. At the same time, the peripheral nervous system—the part of the nervous system in charge of involuntary actions—sends a signal to release the hormone adrenaline to temporarily heighten her blood pressure and give her muscles a boost to respond quickly.

Any time you add up the price of groceries in your basket, follow a recipe, or copy a line drawing, you're using your working memory. This is the memory your brain uses to temporarily store information used in short-term reasoning and planning. Much of the information in the working memory may be forgotten within a short time. For example, if someone tells a cyclist about an upcoming water station, once she's stopped for water she may forget where it is.