If our minds have limited processing power, then cognitive beings need to be strategic about how that resource is used. What we think about, then, is what our brain considers important at the time. For example, your brain is constantly bombarded by sensory information from all over your body, but you are not always aware of it because it is not always deemed all that important. Of course, if your brain started to detect a large amount of pain information coming in from your hand, it makes sense you would suddenly be aware of what your hand is feeling (and why it hurts). Meanwhile, while you were reading this, your lungs were taking in air, but chances are you were not particularly aware of the sensation in your chest, the sound your breath makes, and even how often you breath in and out. Automatic breathing is great for most of the time when we have more important things to concentrate on. But if we need to hold our breath underwater, where an ill-timed breath could be fatal, we take over with controlled breathing, perhaps at the expense of being able to calmly focus on learning psychology concepts.
So a central concept to cognitive psychology is that motivation determines allocation – the importance of information (sensory, like touch, or factual, like a set of statistics) determines what proportion of your available resources will be consumed about it. If you are running from a bear, the sensation of being thirsty is hardly important enough to pay attention to. If you are interested in politics, you might listen closely to a debate and reach a judgment based on the quality of each candidates’ arguments. If you are not so interested (low motivation) or are distracted by homework (high cognitive load), you might only think about their appearance, manner of speaking, and how the crowd reacts to their speech… things that are easily processed in an automatic, subconscious way.
Here is one more example that we can all relate to, known as the cocktail party effect. You are in a crowded room full of conversations and you are having one of your own, and then suddenly you hear someone else say your name in their conversation. Your brain was subconsciously eavesdropping the whole time, but the information did not seem important enough to interrupt you… until it detected your name. If someone is talking about you, it might be important enough to shift your resources over to that conversation.The cocktail party effect can also work if someone is talking about something that is important or relevant to you. For example, I am from Nebraska, so if I overhear someone talking about Nebraska, it will draw my attention.