Viewing disturbing news footage on television could intensify stress and trauma, according to a latest study.
A month before the terrorist attacks on Sep 11, 2001 in the US, sleep and memory researcher Ruth Propper, at Merrimack College in North Andover, Massachusetts, US, began teaching a class in which students had to record their dreams on the mornings that they remembered them.
On the day after the terrorist atrocities, which included using passenger airliners to destroy New York City's World Trade Center towers, Propper "realised there was a valuable opportunity to find out what impact both media coverage and social interactions were having on individuals through the course of this tragedy".
She distributed a questionnaire to the class asking them about their activities the day before, including how much television they watched. The 11 students in the class continued recording their dreams until the end of the semester, three months later.
The students recorded a total of 150 dreams, which Propper and colleagues analysed. They found that nine percent of the 55 dreams collected before Sep 11 contained imagery such as smoke, explosions, police and aircraft.
After the attacks, the proportion doubled, so that 20 percent of students' dreams contained this type of imagery.
But for every hour of television watched beyond three hours on Sep 11, the students' chance of having a dream with that imagery increased by 6 percent.
A student who watched 12 hours of TV on the day of the attacks had a 70 percent chance of having such dreams in the following weeks, Propper was quoted as saying by online edition of The New Scientist.
The researchers say their dream analysis shows that viewing television coverage of a traumatic event can intensify stress and trauma. Some psychologists, however, object to this conclusion, contending that dreams do not necessarily reflect a person's mental state.