of conscious effort. Errors occur due to a misassignment of the weight of certain aspects of memories: assigning high importance to visual information would mean that having poor details of this aspect would be cause for an assumption that the event did not happen or was imagined. Errors will occur if an individual's subjective logic leads them to perceive an event as unlikely to occur or belong to a specific source, even if the truth is otherwise. Simple memory decay can be a source for errors in both judgements, keeping an individual from accessing relevant memory information, leading to source-monitoring errors. Types There are three major types of source-monitoring: external source-monitoring, internal source-monitoring, and reality monitoring, all of which are susceptible to errors and make use of the two judgment processes. External source-monitoring This type of source-monitoring focuses on discriminating between externally retrieved sources, such as events happening in the world surrounding the individual. An example of this is determining which one of an individual's friends said something rude. Internal source-monitoring This type of source-monitoring focuses on discriminating between internally derived sources, such as the individual's memories. An example of this is differentiating between memories of thought ideas and spoken ideas. Reality monitoring This type, also known as internal-external reality monitoring, is derived from the previous two types and focuses on discriminating between internally and externally retrieved sources. An example of this is discriminating a plane crashing into a building portrayed in real life and in a newspaper. This internal-external distinction also applies to the ability to separate events from our past and imagined future events in our memory. People make fewer reality-monitoring errors when searching memory for future events compared with past events, possibly because the features characterizing future events (e.g., cognitive operations) are used more effectively during reality monitoring than features characterizing past events (e.g., perceptual details). These reality-monitoring errors can be reduced in younger adults for events that have more perceptual details and more cognitive operations. In older adults, the more detailed events do not help reduce these autobiographical reality-monitoring errors, possibly due to limits in processing resources. Relationship to brain Observations have been made that indicate a relationship between the prefrontal cortex of the brain and source-monitoring errors. These errors can be seen in everyone, but often are increased in amnesic patients, older adults, and in patients who have organic brain disease with frontal lobe damage.