Thirty-two volunteers who lived through eight short NASA HERA missions gave researchers a close look at what happens when confinement and sleep loss meet in the same spaceflight-style setting. One result stood out quickly. After a partially sleepless night in the first campaign, participants became less accurate at reading facial emotions, even though many other test scores did not shift as clearly.
The finding comes from a Frontiers in Physiology paper published in 2020 by Mathias Basner, Erin Hermosillo, Jordanelle Nasrini and colleagues. Their study followed four one-week missions and four two-week missions inside the Human Exploration Research Analog, a habitat at NASA Johnson Space Center that lets scientists test isolation, workload and operational strain without leaving Earth.
For future crews, the result reaches beyond one lab score. Long missions depend on how well people read each other when they are tired, confined and pressed for time. A crew member does not need to misread every face for problems to begin. A small drop in social judgment can make conflict harder to defuse, feedback harder to interpret and teamwork harder to sustain across many days in a sealed environment.
Why facial emotion reading matters in confinement
Facial emotion identification is one of the quiet mental skills that keeps crews coordinated. People use it when they judge whether a teammate is worried, overloaded, frustrated or simply focused. In a habitat where privacy is limited and work schedules are tight, that skill helps shape trust and timing during ordinary conversations as well as urgent decisions.
Space agencies care about that because analog missions compress several stressors into one setting. NASA describes HERA as a facility for studying isolation, confinement and remote operations under exploration-like conditions. The same environment that tests checklists, workload and sleep also tests whether people can keep interpreting one another accurately when their reserves begin to thin.
Sleep loss has already shown broad effects on cognition in controlled studies. A Sleep paper on the Cognition battery reported that some tasks in the battery respond strongly to reduced sleep, especially tests of vigilance and speed. The HERA study asked a sharper question inside a mission-style setting: would curtailed sleep also dent the more social side of performance, including how people read human expressions?
That question matters because social errors can linger after the moment passes. A delayed reaction on a screen test is easy to spot and easy to score. A subtle mistake in reading another person’s face can change tone, trust and cooperation without producing a single dramatic event. For psychology researchers, that makes emotion reading a useful window into how crews may handle interpersonal strain before an obvious operational breakdown appears.
How NASA’s HERA sleep challenge was set up
The team studied 32 healthy participants across two HERA campaigns. Campaign 1 included four one-week missions and campaign 2 included four two-week missions. Each mission used four-person crews living inside the habitat while following schedules designed to resemble operational spaceflight demands. NASA’s facility information sheet describes the habitat as a closed, multi-level testbed linked to mission control and built for human research under isolation and confinement.
Researchers measured performance with the Cognition battery, a standardized set of computerized tasks that samples several mental functions. One of those tasks was the Emotion Recognition Task, which shows faces expressing different emotions and asks the participant to identify them. The study also tracked alertness, workload, mood and sleep-related complaints so the team could compare test performance with subjective strain.
The sleep manipulation differed between the two campaigns. In campaign 1, participants faced a night of partial sleep restriction. In campaign 2, the challenge was stronger and involved total sleep deprivation sessions. The broader paper reports changes across several tasks, but the facial-emotion result was especially clear in the first campaign, where accuracy dropped during the restricted-sleep phase and recovered afterward.
Scientists designed the setup to separate ordinary practice effects from mission effects as much as possible. Participants were tested at baseline, during the mission and again after the sleep challenge. A later review on short-term isolation and confinement points out that analog environments can affect mood, sleep and higher cognition together, which is why a mission-style design matters more than a single night in a standard sleep lab.
What the HERA team found after curtailed sleep
The paper reports that the Emotion Recognition Task showed a significant effect of the sleep challenge in campaign 1. Participants identified fewer emotions correctly after sleep restriction and after sleep deprivation than they did at baseline and recovery. The effect remained significant after correction for multiple testing, which matters because the study examined many outcomes across the battery.
A closer look at the categories showed that the decline touched most facial expressions, although the shifts for happiness and sadness did not reach statistical significance on their own. The broad pattern still pointed in one direction: after curtailed sleep, participants were less dependable at decoding human faces. That result arrived earlier and more cleanly than many readers might expect from a study framed around operational cognition.
Campaign 2 showed a different emphasis. Under total sleep deprivation, participants became slower and less accurate on the psychomotor vigilance task and they also slowed on tests such as digit-symbol substitution and motor praxis. Those changes fit the classic picture of lost sleep harming sustained attention and processing speed. The facial-emotion finding from campaign 1 therefore helps fill in a different part of the map, because it reaches into social cognition rather than only speed and vigilance.
The authors also recorded clear shifts in self-reported state. Participants were more likely to report tiredness during the sleep challenge and the longer survey in campaign 2 found worse sleep quality, higher workload, greater sleepiness, physical exhaustion and mental fatigue. Another recent paper on cognitive performance in ISS astronauts shows that operational environments can alter several mental domains at once, which makes the HERA pattern easier to place in a larger exploration context.
Why the result matters for future crews
Future exploration crews will spend long stretches in cramped habitats, with delayed communication and limited ways to step away from one another. If a modest amount of lost sleep can weaken emotion reading before broader collapse becomes obvious, crews may need protection strategies that go beyond simple sleep-duration targets. Scheduling, private recovery periods and monitoring of interpersonal strain could all matter.
NASA and other agencies already use analogs to learn which skills erode first under combined stress. The NASA overview of HERA explains that the habitat is meant to simulate the isolation and remoteness of exploration scenarios. Within that setting, the present study suggests that social interpretation deserves the same attention often given to reaction time, memory load and fatigue complaints.
The study is not a verdict on every crew or every mission. HERA is an analog, the missions were short and the sample was limited. Even so, the signal is useful because it shows where cracks may appear first. A crew can keep completing procedures while still reading one another less accurately and that quiet drift can influence morale, coordination and conflict management before a more visible performance drop takes over.
If mission planners want more resilient teams, this paper offers a practical clue. Protecting sleep protects more than alertness. It may also help preserve the fine-grained human judgments that let small crews live and work together in sealed environments where a teammate’s face can be one of the first important signals in the room.
