The latter participants failed to encode the images with the original learning of the event. Thus, it may be the images themselves that lead some of the participants to recall more details of the event. Graphic images may make an individual associate more with the horror and scale of a tragic event and hence produce a more elaborate encoding mechanism. Furthermore, perhaps looking at images may help individuals retain vivid flashbulb memories months, and perhaps even years, after an event occurs. The special-mechanism hypothesis has been the subject of considerable discussion in recent years, with some authors endorsing the hypothesis and others noting potential problems.This hypothesis divides memory processes into different categories, positing that different mechanisms underlie flashbulb memories. Yet many argue that flashbulb memories are simply the product of multiple, unique factors coalescing. Data concerning people's recollections of the Reagan assassination attempt provide support for the special-mechanism hypothesis. People had highly accurate accounts of the event and had lost very few details regarding the event several months after it occurred. Additionally, an experiment examining emotional state and word valence found that people are better able to remember irrelevant information when they are in a negative, shocked state. There is also neurological evidence in support of a special mechanism view. Emotionally neutral autobiographical events, such as a party, were compared with two emotionally arousing events: Princess Diana's death, and Mother Teresa's death. Long-term memory for the contextual details of an emotionally neutral autobiographical event was significantly related to medial temporal lobe function and correlated with frontal lobe function, whereas there was no hint of an effect of either medial temporal lobe or frontal lobe function on memory for the two flashbulb events. These results indicate that there might be a special neurobiological mechanism associated with emotionally arousing flashbulb memories. Studies have shown that flashbulb memories can result from non-surprising events, such as the first moon landing, and also from non-consequential events. While Brown and Kulik defined flashbulb memories as memories of first learning about a shocking event, they expand their discussion to include personal events in which the memory is of the event itself. Simply asking participants to retrieve vivid, autobiographical memories has been shown to produce memories that contain the six features of flashbulb memories. Therefore, it has been proposed that such memories be viewed as products of ordinary memory mechanisms. Moreover, flashbulb memories have been shown to be susceptible to errors in reconstructive processes, specifically systematic bias. It has been suggested that flashbulb memories are not especially resistant to forgetting.