Night or darkness, which intensifies the feeling of fear?

Nighttime fear is a phenomenon in which people feel more afraid of threats at night. Despite the vast amount of psychological research on nighttime fear, previous researchers have not accurately distinguished between "night" and "darkness", both of which play important roles in nighttime fear. We collected physiological (skin conductance response and heart rate) and psychological (self-report) data simultaneously to investigate the effects of "night" and "darkness" on fearful feelings and whether these effects were moderated by the mode of stimulus delivery (i.e., visual or auditory). Specifically, two tasks were employed in which time (day vs. night), illumination (light vs. darkness) and stimulus type (fearful vs. neutral) were manipulated. Participants (n=128) were exposed to visual and auditory oddball tasks consisting of fearful and neutral stimuli. The results indicated that there were significant increases in fear responses at night, and the difference between day and night was significant for fear stimuli but not for neutral events. Furthermore, these effects were consistent over different sensory modalities (visual and auditory). The results of this study underscore the importance of the day-night cycle in fear-related information processing and suggest that further attention needs to be paid to the influence of the biological circadian rhythm on these processes. The current findings could inform a deeper understanding of anxiety and fear-related disorders, and thus, we invite future studies to illuminate the underlying neurobiological mechanisms therein.