The still face experiment is a developmental psychology procedure that reveals how powerfully babies depend on emotional feedback from their caregivers. First described by Edward Tronick and colleagues in 1978, it uses a simple, striking setup: a parent plays normally with their infant, then suddenly goes emotionally blank. Within seconds, the baby’s behavior changes dramatically, showing that even very young infants are active participants in social interaction, not passive observers.
How the Experiment Works
The procedure has three phases, each typically lasting about two minutes. In the first phase, the caregiver plays with the infant face-to-face as they normally would at home, talking, smiling, and responding to the baby’s cues. This establishes a baseline of natural interaction.
In the second phase, the caregiver suddenly stops all interaction. They maintain a neutral, expressionless “poker face” while still looking at the infant. They don’t smile, talk, nod, or touch the child. If the child offers a toy, the caregiver doesn’t accept it. This is the still face episode.
In the third phase, called the reunion, the caregiver resumes normal interaction. This final phase is just as important as the still face itself, because it reveals how well the infant can recover from the disruption. The original 1978 version actually only had two phases (normal interaction and still face), but the three-phase version with the reunion became the standard format used in hundreds of studies since.
What Babies Do When a Parent Goes Blank
The infant’s reaction is what makes this experiment so striking, and why videos of it have spread widely online. During normal play, babies are animated. They smile, vocalize, make eye contact, and mirror their caregiver’s expressions. When the still face begins, babies don’t just passively accept the change.
First, they try to get their parent’s attention back. They smile bigger, vocalize more, reach out, and make exaggerated facial expressions. Research using the paradigm has shown that non-cry vocalizations actually peak during the middle of the still face period, as babies ramp up their efforts to re-engage. When those bids fail, the infant’s behavior shifts. Smiling and eye contact decrease over time, while cry-face expressions increase. Babies begin to look away, self-soothe by sucking their fingers or touching their own bodies, and some eventually become visibly withdrawn and dejected.
This progression, from active bidding to withdrawal, is what Tronick and his colleagues originally described: infants gradually cease attempts to re-establish interaction when they can’t get a response.
The Reunion Phase and Carry-Over Stress
When the caregiver resumes normal interaction in the reunion phase, most babies recover, but not immediately and not completely. One consistent finding across studies is that infants don’t simply snap back to their baseline behavior. They often show less eye contact during the reunion than they did during the initial play, and some continue to display signs of distress even after the caregiver is fully engaged again. This lingering effect, sometimes called the “carry-over” effect, suggests that even a brief period of emotional unresponsiveness leaves a temporary mark on the infant’s emotional state.
Studies have also found that the length of the reunion matters. When reunion episodes are shorter than two minutes, infants show an even stronger decrease in gaze compared to baseline, possibly because they haven’t had enough time to fully re-regulate.
What’s Happening in the Baby’s Body
The emotional distress visible on an infant’s face during the still face phase has a physiological counterpart. Research measuring cortisol, the body’s primary stress hormone, has found that the still face experience can trigger a measurable stress response, but not in all babies equally. Infants who display sadness during the still face episode show increases in cortisol, while those who respond with anger or a more neutral expression do not. This means the baby’s emotional interpretation of the experience, not just the experience itself, shapes the physical stress response.
What It Reveals About Emotional Development
The still face experiment demonstrated something that wasn’t widely appreciated in the 1970s: infants are not simply receiving care. They are actively co-creating social interactions with their caregivers. When that back-and-forth exchange is disrupted, babies have a repertoire of strategies to try to repair it. This concept, called mutual regulation, became central to understanding how emotional development works in early life.
The experiment also connects to attachment theory in a practical way. The still face is essentially a micro-dose of caregiver unavailability. How an infant responds, and how quickly they recover during reunion, offers a window into the quality of the relationship. Babies who have experienced consistent, responsive caregiving tend to bid more actively and recover more smoothly. The still face paradigm became one of the most widely used tools in infant research precisely because it captures this dynamic in just six minutes.
Infants of Depressed Mothers Respond Differently
One of the most revealing applications of the still face experiment has been in studying the effects of maternal depression. A meta-analysis of studies on this topic found that infants of depressed mothers do show the classic still face effect: less positive emotion, more negative emotion, and reduced eye contact. But they also display something unexpected. During the still face episode, these babies actually show more positive expressions than babies of non-depressed mothers.
Researchers interpret this in two ways. First, these infants may have learned from daily experience that their mother is often emotionally unavailable, so they’ve developed a strategy of amplifying positive signals, essentially working harder to get a response. Second, the increased smiling may serve as a self-regulation tool, a way for the baby to manage their own distress. Either way, it suggests that babies are already adapting their social strategies based on the patterns of interaction they’ve experienced at home.
The Smartphone Version
In recent years, researchers have adapted the still face paradigm to study something very modern: what happens when a parent’s attention shifts to a phone instead of going completely blank. In a mobile phone version of the experiment, the caregiver looks at their phone during the still face phase rather than maintaining a neutral expression.
The results closely mirror the classic version. Infants show increased negative emotion, decreased positive emotion, more self-comforting behaviors, and more attempts to escape the situation during the phone-distracted phase. Many babies fail to return to their baseline emotional state during the reunion. Parents who reported more frequent phone-related interruptions in daily life (sometimes called “technoference”) had infants who showed more escape behaviors during the experiment. Interestingly, higher levels of daily technoference also appeared to blunt the infant’s negative emotional response during the still face, echoing the pattern seen with depressed mothers: babies who experience more routine disconnection may adapt to it, but that adaptation isn’t necessarily a sign of resilience.
Why It Matters Beyond the Lab
The still face experiment isn’t meant to suggest that every moment of parental distraction harms a child. Brief ruptures in attention are normal and inevitable. What the experiment captures is the fundamental importance of responsive interaction in the earliest months and years of life. Babies are wired to seek emotional connection, and they notice almost immediately when it disappears. The fact that they actively try to repair the break, and show measurable stress when they can’t, tells us that social engagement isn’t a luxury for infants. It’s a biological expectation.
The paradigm has been adapted for children as old as two and a half, with similar results. In these versions, toddlers play freely with their caregiver before the still face phase, and they show the same pattern of increased bids followed by withdrawal when their parent becomes unresponsive. The consistency of these findings across ages, across cultures, and across variations of the procedure is part of what makes the still face experiment one of the most replicated and influential demonstrations in developmental psychology.