Facial Feedback Hypothesis

Mind-Body & Emotion

Strack, Stepper and Martin (1988)

Can the mere act of smiling improve our mood?


If someone is smiling and seems in a good mood, folk psychology (our common understanding of human behavior before we actually study psychology) would tell us that they are smiling because they are in a good mood. But what if it was the other way around? What if their smile was the cause, and not the effect, of their good mood?

This apparently strange idea is known as the Facial Feedback Hypothesis (Strack, Stepper and Martin, 1988). This theory focuses on the role of peripheral physiological reactions in the experience of emotion, and more specifically on facial muscular activity. Indeed, Darwin (1872) himself suggested that, “in the presence of an eliciting emotional stimulus, a person’s emotional experience can be either strengthened or attenuated, depending on whether it is or is not accompanied by the appropriate muscular activity” (Strack, Stepper and Martin, 1988). On that basis, the Facial Feedback Hypothesis proposes that “facial feedback has a small but reliable moderating effect on the emotional experience and on the evaluation of emotional stimuli” (Kraut, 1982).

Two different explanations of this phenomenon have been proposed:

  • Laird (1974) theorized that it was due to a cognitive mechanism: self-perception. Seeing that they are smiling, people would infer that they are in a good mood.
  • However,  Strack, Stepper and Martin (1988) believed that such a détour was unnecessary and that physiological mechanisms were sufficient. An innate biological program would directly prompt us to be in a good mood when we smile.

Participants & Procedures

92 male and female undergraduates from the University of Illinois (Urbana-Champaign, IL, USA).

Participants were assigned to one of four cubicles (to prevent communication), where they found a marker, an alcohol swab, and a booklet. As presented by the experimenter, the study focused on psychomotor coordination and the ability to perform usual tasks with unusual body parts. Depending on the condition, participants were then instructed to hold the marker (after disinfecting it!) with their non-dominant hand, their teeth, or their lips. Using detailed instructions and demonstrations, the researchers made sure that the participants held the marker properly, i.e., either with protruding lips (so that it didn’t touch their teeth), or with extended lips (so that it only touched their teeth). In reality, the “Teeth” condition was meant to facilitate the activation of the facial muscles associated with smiling, while the “Lip” condition was meant to  inhibit it (and induce a frown.) The non-dominant “Hand” condition was simply a control. The booklet contained four different exercises: drawing a straight line between two points, drawing a line between ten ordered digits, underlining vowels in words, and scoring four magazine cartoons borrowed from Gary Larson’s The Far Side on a scale of 0 (not funny at all) to 9 (very funny). At the end of the experiment, participants also rated the difficulty of the tasks. Of course, funniness ratings were the only relevant dependent variable.


As can be seen from the table below, the researchers’ hypothesis was confirmed: the cartoons were rated least funny when the activity of the muscles associated with smiling was inhibited with a frown (“Lip” condition), and most funny when this activity was facilitated (“Teeth” condition).

The effect size was small, but consistent and statistically significant. The perceived difficulty of the tasks did not have a meditating effect. Thus, the findings corroborated the Facial Feedback Hypothesis and suggested that the cognitive interpretation of one’s facial expression was not necessary to influence the emotional reaction to a stimulus and its evaluation. Indeed, as far as they knew, participants were not  “smiling” or “frowning”, but simpluy holding a pen in their mouth. Thus, physiological mechanisms were likely sufficient to translate the activation of specific facial muscles into a positive emotional predisposition.

IA Tip

In line with IB guidelines, we recommend that students only compare two conditions in their experiment and obtain a single measurable result for each participant in each condition. Doing otherwise would complicate inferential statistics without any benefit as far as the IA is concerned. 

Here, students can simply compare the “Teeth” and “Lip” OR “Hand” conditions. Likewise, they can compare scores on a single cartoon. The filler tasks involved in the experiment can, of course, also be modified as long as participants hold something with their teeth long enough while completing them in one of the conditions.


Strack, F., Martin, L. L., & Stepper, S. (1988). Inhibiting and facilitating conditions of the human smile: a nonobtrusive test of the facial feedback hypothesis. Journal of personality and social psychology, 54, 768–777.