Our jumpiness at nighttime is not just because it's dark

When something goes bump in the night, most of us are little jumpier than we would be in the day. But is that just because it’s dark, or is it more to do with our bodies and brains switching to a vigilant nocturnal mode?

Yadan Li and her colleagues have attempted to disentangle the influences of darkness and nighttime. They recruited 120 young women to complete a computer task in a windowless cubicle, which involved them looking at neutral pictures (e.g. nature scenes), scary pictures (e.g. spiders; a person being attacked), and listening to scary sounds (e.g. screams) and neutral sounds (e.g. bird song).

The women were split into four groups: some of them completed the task in the day-time with bright lights on; some in the day-time in darkness; others at night-time with a dim light on; and others at night-time in complete darkness (although presumably the computer screen created some light).

The women who completed the task at nighttime said they found the scary pictures and sounds more scary (than the women tested in the day-time), and this was true regardless of whether they were tested in darkness or light. Moreover, their extra jumpiness was confirmed by recordings taken of their heart-rate and perspiration.

In contrast, the time of testing made no difference to the women’s responses to the neutral pictures and sounds. Also, the lighting levels, whether in the day-time or at nighttime, made no difference to the women’s reactions to the neutral or scary stimuli.

In other words, the findings appear to suggest that we’re more sensitive to threats at nighttime because it’s the night, not because it’s dark. This raises the possibility that biological factors associated with our circadian rhythm affect our fear-sensitivity, although it’s plausible that cultural factors are involved, in that we’ve learned to be more vigilant at night.

The day-time testing took place at 8.00am and the nighttime testing at 8.00pm (in February, so it was dark outside) – it remains to be seen whether and how the findings might vary at different times of day and night. We also don’t know if the same findings would apply to male participants, or participants from different cultures or stages of life (the study was conducted in China where the authors are based, and the student participants had an average age of 22 years).

Li and her colleagues hope their findings will inspire other researchers to explore this topic. “[T]his study is merely a first step in understanding the underlying mechanisms involved in fear-related information processing and has implications for the underlying psychopathology of relevant phobias and anxiety disorders [such as nighttime panic attacks],” they said.

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Li, Y., Ma, W., Kang, Q., Qiao, L., Tang, D., Qiu, J., Zhang, Q., & Li, H. (2015). Night or darkness, which intensifies the feeling of fear? International Journal of Psychophysiology DOI: 10.1016/j.ijpsycho.2015.04.021

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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