The curve looks like an upside-down U — Page 129, Lesson 199

I want to walk you through the relationship between arousal, stress, and performance, and then into the body's stress reaction mechanism. Let's start with the Yerkes-Dodson principle, which is the core idea here. We have a graph — Figure 7.2 — that shows arousal, which is another word for stress level, on the horizontal axis, and performance on the vertical axis. The curve looks like an upside-down U. At the left side, where arousal is low, performance is also low. When arousal is too low, the individual is not fully functioning. You have a slow environmental scan — meaning you're not picking up information from your surroundings efficiently — and you may miss information. So performance is low. As we move to the middle of the curve, we reach the optimal arousal level. At this point we are at our most efficient. We have enough demands to keep our attention engaged, and we have the capability to deal with complex tasks. This is the peak of the curve. Now, as we move to the right side of the curve, into high arousal levels, our performance starts to deteriorate. Errors are made, and information may be missed. We suffer from a narrowing of attention — we tend to focus on a limited source of data. At very high arousal levels, we experience overload. We reach a limit of processing capacity, or a limit of our ability to complete all the tasks. This overload funnels our attention to events that we perceive as being relevant to the perceived primary task. So information may be missed from important but more peripheral and non-attended sources. At these high levels, the attention mechanism can reject vital information solely due to overload. That's the Yerkes-Dodson relationship between arousal and performance. Now let's move into the stress reaction itself, which is described by the General Adaptation Syndrome, or GAS. The General Adaptation Syndrome is the term used to describe the mechanism by which the individual reacts to an outside real, perceived, or anticipated threat. So it's not just actual danger — it can be something you think might happen or expect to happen. The syndrome is triggered by the arousal mechanism, which operates through the Autonomic Nervous System, or ANS. The ANS controls many of the body's essential functions: respiration, circulation, digestion, and so on — functions over which we normally have no conscious control. The state of homeostasis — that's the body's stable internal balance — is maintained by this system. The ANS is divided into two branches. The first is the Sympathetic branch. The second is the Parasympathetic branch. These control systems are neurohormonal in their makeup — meaning they use both nerves and hormones to communicate — and they are highly self-regulated under normal circumstances. So to summarise: we have the Yerkes-Dodson curve showing that low arousal gives low performance, optimal arousal gives peak performance, and high arousal causes deterioration and overload. Then we have the General Adaptation Syndrome, triggered by the Autonomic Nervous System, which is the body's mechanism for reacting to threats. The ANS has two branches — sympathetic and parasympathetic — and it maintains homeostasis through neurohormonal control.