Boredom doesn't take just one -- or even four -- forms, according to researchers who say they have identified a fifth variant on the emotional state.

In 2006, Thomas Goetz of the University of Konstanz and his colleague Anne Frenzel identified four types of boredom based on arousal levels and so-called valence, or how positive or negative boredom is experienced. The four categories included:

  • Indifferent boredom, defined as being relaxed, withdrawn and indifferent

  • Calibrating boredom, defined as being uncertain and receptive to change/distraction

  • Searching boredom, defined as being restless and in active pursuit of change/distraction

  • Reactant boredom, defined as being motivated to leave a situation for specific alternatives

Joining the list now is apathetic boredom, characterized as "an especially unpleasant form that resembles learned helplessness or depression," according to the news release outlining the study.

Carried out by Geotz and Frenzel as well as others, the study included two real-time experience studies lasting two weeks. During it, 63 German university students and 80 German high school students completed digital questionnaires about their activities and experiences throughout the course of a day using a personal digital assistant device.

The high school group reported especially high levels of apathetic boredom, with 36 percent saying they experienced the emotion relatively frequently -- a revelation the researchers found concerning given the assumed link between boredom and depression.

According to the findings, the type of boredom a person experiences depends largely on the context of his or her experiences, rather than the intensity of the boredom felt. Furthermore, they found that people tend to experience one category, rather than a range.

"We therefore speculate that experiencing specific boredom types might, to some degree, be due to personality-specific dispositions," Goetz said in a statement.

In regard to how boredom affects learning and achievement, Goetz said: "This question can only be adequately answered if we know what type of boredom a student experiences."