Sleep deprivation undermines the link between identity and intergroup bias.

This research seeks to bridge two findings-on the one hand, top-down controlled processes inhibit display of intergroup bias; on the other one hand, sleep deprivation impairs cognitive control processes. Connecting these two proven statements, begs the question: would sleep deprivation also influence intergroup bias? This intriguing link has hardly been explored in extant literature. To fill this gap, we theorize through the lens of social identity. Previous research has shown that individuals who share a common identity with an outgroup are more motivated to inhibit biases toward the outgroup than do their counterparts who do not endorse such common identity. We predicted that this motivated inhibition would be compromised by sleep deprivation. Across two studies, as predicted, we found that only when an individual has adequate sleep did common ingroup identity attenuate the display of intergroup bias, whereas individuals with short habitual sleep (study 1) or after one-night sleep deprivation (study 2) displayed equally high levels of intergroup bias regardless of their high or low levels of common ingroup identity. In the global context of incessant intergroup bias and diminishing sleep time, our findings offer new insights for understanding and handling intergroup bias.