One pleasant Saturday morning, my wife and I were sitting on our outdoor deck, watching a robin drink from our birdbath, when all of a sudden we heard a loud “swoosh” above our heads. Looking up, we caught the shadow of a red-tailed hawk, dropping like a thunderbolt from its perch in a nearby tree, grabbing the helpless robin by the throat. As the raptor swooped by us, not three feet away, blood from the robin splattered on our table. What started as a leisurely repast ended as a violent reminder of the savagery of the real world. We were stunned into silence.
In Posner’s model, the brain’s first system functions much like the two-part job of a museum security officer: surveillance and alert. He called it the Alerting or Arousal Network. It monitors the sensory environment for any unusual activities. This is the general level of attention our brains are paying to our world, a condition termed “intrinsic alertness.” My wife and I were using this network as we sipped our coffee, watching the robin. If the system detects something unusual, such as the hawk’s swoosh, it can sound an alarm heard brain-wide. That’s when intrinsic alertness transforms into specific attention, called phasic alertness.
After the alarm sounds, we orient ourselves to the attending stimulus, activating the second network: the Orienting Network. We may turn our heads toward the stimulus, perk up our ears, perhaps move toward (or away) from something. It’s why both my wife and I immediately lifted our heads away from the robin, attending to the growing shadow of the hawk. The purpose is to gain more information about the stimulus, allowing the brain to decide what to do. The third system, the Executive Network, controls what action we take next. Actions may include setting priorities, planning on the fly, controlling impulses, weighing the consequences of our actions, or shifting attention. For my wife and me, it was stunned silence, until one of us moved to clean off the blood.
So we have the ability to detect a new stimulus, the ability to turn toward it, and the ability to decide what to do based on its nature. Posner’s model offered testable predictions about brain function and attention, leading to neurological discoveries that would fill volumes.