Something does not seem quite right. The most powerful man in the world, John F. Kennedy, was taken out by a lone nutjob of no previous consequence? A jet flies into the pentagon and yet the expected debris is not visible. And why can’t I see stars in the NASA Apollo moon landing photos?

Some hidden agent must be at work, conspiring to deceive and carry out some sinister plot.

At least that is how our brains are hardwired to think, and some of us more than others. This tendency has been termed the “hyperactive (or hypersensitive) agency detection device” –  HADD – coined by Justin Barrett. Understanding that HADD is an intrinsic part of human nature is part of the core knowledge base of the skeptic.

As a neurologist and a skeptic I am particularly interested in how brain function relates to human intellectual strengths and weaknesses and how knowledge of such helps us to avoid common mental pitfalls. In other words, knowledge of how the human brain works helps us think better – to be more skeptical and avoid error.

Psychologists and neuroscientists in recent years have demonstrated that our brains are hardwired to distinguish things in our environment that are alive from those that are not alive. But “being alive” (from a psychological point of view) is not about biology, but agency – something that can act in the world, that has its own will and can cause things to happen. Sure, this is a property of living things, but that’s not how our brain sort things out. We can perceive agency in non-living things if they are acting as if they are agents.

This is reflected even in our visual system, which separates out visual information into different streams according to the type of information. One division is between information about actions and information about objects. The object stream is also divided into brain regions that deal with inanimate objects and other regions that deal with living things or animate objects. So on a fundamental level our brains treat agents different than objects – from the moment we see them.

Bruce Hood, author of Supersense, goes over in his book the psychological studies that have documented and described the human tendency to think of objects differently than agents. We imbue agents with an essence – a unique living force, even while infants. Objects are just generic things, totally interchangeable. While agents have their own unique essence. Interestingly, children can come to view a favorite toy (a stuffed animal, for example) with the properties of an agent and will treat it like a living thing. This reinforces the notion that the distinction we make is not between living and non-living so much as agent vs object. This  likely also explains why we can watch a cartoon and react emotionally to the characters as if they were real – they are not living, but we see them as agents.

According to Barrett, HADD works in part by detecting any movement that is non-inertial – something which seems to be moving of its own volition. We then assume it is acting with agency and react accordingly. This likely provided an evolutionary advantage – it is better to assume the rustling in the bushes was not the wind but a hungry tiger. So we are descended from hominids who were more paranoid and had hyperactive agency detection, because they were less likely to be eaten by predators.

We can extrapolate from “non-inertial movement”, or movement that cannot be easily explained as a passive reaction to natural forces, to more and more complex “actions.” HADD detects more than movement, it can detect a pattern in otherwise unrelated events, details that defy easy explanation, or consequences that seem out of proportion to the alleged causes. When HADD is triggered we tend to see a hidden agent working behind the scenes, making events unfold the way they do, and perhaps even deliberately hiding its own tracks.

When HADD is triggered and we think we see the hidden agent, it speaks to us in a very primal way. For some people the perception of hidden agency becomes overwhelming, dominating all other thought processes. We know these people as conspiracy theorists. But there is a little conspiracy theorist inside each of us.

Studies have also demonstrated that HADD is more likely to be triggered when a stimulus is ambiguous – therefore it tends to be our default assumption – an object is an agent until we are sure it’s just an object. Also, in situations where we have less control our HADD becomes more active still.

Barrett and others have speculated that HADD is important to the development of religion – where God is the ultimate invisible agent. So far this hypothesis has not been significantly researched, but it does seem reasonable. Seeing natural or random events as the will of an agent is HADD.

HADD also leads to superstition – thinking that there is a cause and effect between unconnected events. The underlying assumption of superstitions is that things happen for a reason (a vague ill-defined reason, but a sense that there is a hidden agency at work). I think it is liberating to understand that rather (as was most elegantly stated on a bumper sticker) “shit happens.”

Skepticism, in many ways, is a filter on HADD. First we have to recognize that our brains are not perfect perceivers and processors of information. There are specific and myriad ways in which the human brain is biased and flawed. Science and skepticism are methods for correcting or filtering out those biases. Skeptics ask themselves – is it really true. We see many patterns, but only some of those patterns represent underlying reality. We need a process to sort out which ones are real – that is science and skepticism.