When sensory information enters the brain, it travels along two paths.
One leads to conscious awareness. Within about half a second, messages on this path are observed and analyzed to see if action is necessary. For example, say you’re a few car lengths from an intersection when you see the traffic light turn orange. You consciously decide whether to brake or to keep going.
Sensory messages also zip to the unconscious, where they’re immediately assessed by the amygdala, a part of the brain that’s always on the lookout for danger. Say you decide to keep going despite the orange light. You’ve just entered the intersection when, from the corner of your eye, you see a big blur rushing at you from the side.