Dreams are more negative than real life: Implications for the function of dreaming

Abstract

Dream content studies have revealed that dream experiences are negatively biased; negative dream contents are more frequent than corresponding positive dream contents. It is unclear, however, whether the bias is real or due to biased sampling, i.e., selective memory for intense negative emotions. The threat simulation theory (TST) claims that the negativity bias is real and reflects the evolved biological function of dreaming. In the present study, we tested the hypothesis of the TST that threatening events are overrepresented in dreams, i.e., more frequent and more severe in dreams than in real life. To control for biased sampling, we used as a baseline the corresponding negative events in real life rather than the corresponding positive events in dreams. We collected dream reports (N=419) and daily event logs (N=490) from 39 university students during a two-week period, and interviewed them about real threat experiences retrievable from autobiographical memory (N=714). Threat experiences proved to be much more frequent and severe in dreams than in real life, and Current Dream Threats more closely resembled Past than Current Real Threats. We conclude that the TST's predictions hold, and that the negativity bias is real.

Acknowledgements

The Alfred Kordelin Foundation, the Finnish Cultural Foundation, and the National Graduate School of Psychology provided financial support for this work.

We wish to thank all the participants for their valuable contribution.

Notes

¹The Dream Threat Scale has been previously utilised in four published studies (Revonsuo & Valli, 2000; Valli et al., 2005, 2006; Zadra et al., 2006), and in many unpublished ones (Desjardins & Zadra, 2004; Valli et al., 2007a, 2007b, 2007c), as well as in several unpublished Master's theses (Aitta-Aho, 2006; Myllymaa, 2006; Turunen, 2006). As the interrater reliability has been good or strong in these studies, and the content analysis results have been congruent, we believe that the method is reliable for identifying and classifying threatening events in written reports.

²The odds ratio is a measure of effect size, and is defined as the ratio of odds of an event occurring in one sample to the odds of it occurring in another sample (Stokes, Davis, & Koch, 2000). We expected the odds ratio to reveal whether experiencing a certain type of threat during wakefulness yields it more likely to be simulated in dreams.

³The threats in the autobiographical reports were not identified, as a report including a description of a single threat constituted by definition one threatening event, the agreement thus being 100%.

⁴The autobiographical threat descriptions were not directly comparable to dream reports and daily logs as they were written down during the interview by the interviewer, therefore word count for Past Real Threats is not reported.