Princeton University researchers found that the brain breaks experiences into the "events," or related groups that help us mentally organize the day's many situations, using subconscious mental categories it creates. These categories are based on how the considers people, objects and actions are related in terms of how they tend to — or tend not to — pop up near one another at specific times. Human participants viewed abstract symbols (b) and patterns (c) that — without the their knowledge — were grouped into three "communities" of five symbols or patterns. The shapes followed a sequence (a) in which symbols or patterns in the same community (separated above by color) tended to appear near one another in the sequence (lines within pentagons). Occasionally, a symbol or pattern would appear near one from another community (lines joining separate pentagons). After a half hour of viewing, participants were asked to segment the sequences into events in a way that felt natural to them, and tended to break the sequences into events that coincided with the communities the researchers had prearranged.