A set of high-frequency brain waves may help us unconsciously know when something's different by comparing memories of the past with present experiences.
A recent study shows how the brain uses certain neural activity patterns to compare our expectations with the present. Ultimately, we hope that these results will help us better understand how the brain portrays reality under healthy and disease conditions.
According to the researchers, predictive coding basically states that the brain optimises neural activity for processing information. In other words, the theory forecasts that the brain uses more neural activity to process new information than it does for things that we are familiar with.
Years of research has shown that over time this is how we learn to expect what common sights, like green grass, looks like or everyday noises, such as certain bird chirps, sound like. The researchers wanted to know whether the brain uses a similar process to manage our experiences.
The experiment began when the patients were shown and asked to memorize a series of four natural scenes displayed on a computer screen. For example, one of the scenes was of a brown bicycle leaning upright on a kickstand in front of a green bush. A few seconds later they were shown a new set of images and asked whether they recognised the scene or noticed something different. Some images were the same as before while others were slightly modified by adding or removing something, such as a red bird, from the scene.
On average, the patients successfully recognised 88% of the repeat scenes, 68% of scenes that were missing something, and 65% of the ones in which something was added. In each case, it took them about two and a half seconds to notice.
Further analysis of a subset of the patients showed that they successfully located 82% of additions and 70% of removals. Curiously, their eyes fixated often (83%) on additions but barely at all (34%) on areas in the scene where something was removed.