Schachter-Singer Two-Factor Theory of Emotion

The Schachter-Singer theory, often called the two-factor theory of emotion, proposes that a combination of physiological arousal and cognitive interpretation determines emotions.

This theory was developed by psychologists Stanley Schachter and Jerome E. Singer in the 1960s.

Here’s a breakdown of the theory:

  1. Physiological Arousal: Initially, an event causes physiological arousal. This is the body’s immediate response to a stimulus, which can include reactions such as an increased heartbeat, sweating, and muscle tension.
  2. Cognitive Interpretation: Following physiological arousal, the individual will make a cognitive interpretation or appraisal of the situation to determine the specific emotion they are feeling. This means that the person will search their environment for cues to label and interpret their arousal.

Schachter & Singer (1962)

The Schachter-Singer experiment, often called the “epinephrine study,” was a foundational piece of research for the two-factor theory of emotion.

The Schachter-Singer experiment remains a critical piece of research in understanding emotion, emphasizing the intertwined relationship of physiological responses and cognitive processes.


They wanted to empirically test their two-factor theory of emotion, which posits that emotions are determined by a combination of physiological arousal and the cognitive interpretation or label one assigns to that arousal based on environmental cues.


Male college students were injected with either epinephrine (which induces physiological arousal) or a placebo.

They were then given information about the effects of the injection: some were informed about the true effects, some were misinformed, and some were uninformed.

Following the injection, participants were placed in a room with a confederate who either acted euphorically or angrily. After this interaction, participants were asked about their emotional state.


The study involved 185 male students from the University of Minnesota’s introductory psychology course. They participated for course credit.

Prior health record checks ensured the injection’s safety. A self-selecting sampling method was used.

Experimental Design

Independent measures design was used, with participants randomly allocated to different conditions.

Independent Variable (1): Injection (Arousal)

To do this, they conducted an experiment where participants were injected with either epinephrine, a hormone known to induce physiological arousal, or a saline solution which acted as a placebo.

They would experience side effects within 3 to 5 minutes which would last for an hour.

Independent Variable (2): Informed Condition

Participants were then divided into three groups based on the information they received about the effects of the injection.

  • The informed group was told about the actual side effects of the epinephrine, such as increased heartbeat and jitteriness.
  • The misinformed group was provided with incorrect side effects to ensure they couldn’t correctly attribute their physiological feelings to the drug.
  • The uninformed group was given no information at all about potential side effects.

Independent Variable (3): Confederate Behaviour

Following the injections, participants were placed in a room with a confederate, an individual working with the experimenters.

This confederate behaved in one of two pre-determined ways to create a specific emotional environment.

  • In one scenario, the confederate exhibited euphoric behaviors, playing with hula hoops and making paper airplanes, aiming to foster a joyful atmosphere.
  • In the other scenario, the confederate portrayed anger, expressing frustration about the experiment and the tasks they were asked to complete.


  • All participants were in a waiting room with a confederate, ensuring consistency in environmental factors.
  • The injection was consistent in dosage.

Dependent Variable

The primary dependent variable in the Schachter-Singer experiment was the participants’ emotional response.

Participants filled out a questionnaire after the injection and interaction with the confederate., which gauged their emotional state.

The essence of the dependent variable was to determine how the combination of physiological arousal (epinephrine vs. placebo) and external cues (euphoria vs. anger) led participants to label and experience a specific emotion.

The participant’s self-reports and behaviors were meticulously noted and analyzed to decipher the emotional state they experienced in response to the manipulated variables of the experiment.


  • Participants who received epinephrine and were uninformed or misinformed about the side effects showed more pronounced emotional reactions (either euphoria or anger) based on the behavior of the confederate.
  • Participants who were informed about the side effects of epinephrine (and thus could attribute their physiological arousal to the injection) showed less emotional response, as they did not look to the environment to explain their arousal.

The interpretation of the situation (whether they were with someone acting happy or angry) determined how participants labeled and experienced their own emotion, even though the physiological arousal (from the epinephrine) was the same.


The results supported the Schachter-Singer two-factor theory. When participants couldn’t explain their arousal from the injection, they looked to the environment (the confederate’s behavior) to label their feelings.

Those who could attribute their arousal to the epinephrine didn’t feel the need to seek environmental cues for their emotional state.

The Schachter-Singer theory suggests that emotions are a combination of arousal and how we interpret that arousal based on our environment.

This theory contrasts with other emotion theories, suggesting that specific emotions arise from physiological responses.



  • Participants were deceived about the true nature of the experiment. They were told that they were participating in a study about the effects of a new drug on vision when, in reality, the study was about emotional responses.
  • They were also misled about the effects of the injection. Some were informed correctly (about the epinephrine), some were misinformed, and others were not informed at all.

Informed Consent:

  • While participants consented to be part of a study, they were not fully informed about the actual purpose or the potential effects of the epinephrine. True informed consent requires participants to understand and agree to all aspects of the study they’re involved in.

Protection from Harm:

  • The researchers checked participants’ health records to ensure the injection’s safety, yet there remained a notable risk. A trained doctor administered the injection to safeguard the participants.


  1. Self-reports: Self-report methods, like questionnaires, can be easily administered to large samples.
  2. Controlled design: Allowing for clearer causation between variables. To ensure control in the experiment, all participants were placed in a waiting room with a confederate to maintain consistent environmental conditions, and the dosage of the injection was kept uniform for everyone.
  3. Multiple methods: Using observational and self-report data provides a more comprehensive view of participants’ emotional states. Observational data offers an objective measure of behavior, while self-report data provides insight into participants’ subjective experiences.
  4. Scientific contribution: By providing evidence against prevailing theories and highlighting the importance of cognitive interpretation in emotion formation, the Schachter & Singer (1962) study reshaped the understanding of emotional processes. Challenging and refining existing theories based on empirical evidence is fundamental to scientific advancement.


  1. Self-reports: Participants might answer in a way that they believe is socially acceptable or desirable rather than how they truly feel or think.
  2. Biased sample: The fact that participants were university students might mean they shared some common educational and possibly cultural experiences. This might not reflect the broader population’s emotional responses.
  3. Ethical considerations: injecting participants without full transparency raised concerns.
  4. Individual differences: The study assumes that the given labels (euphoria or anger) were the only interpretations of the confederate’s behavior. It doesn’t account for potential individual differences in interpretation. Adrenalin does not affect everyone in the same way due to individual differences.
  5. Low ecological validity: Some critics argue that the emotional responses in such a controlled and artificial environment might not generalize to real-world situations, such as a job interview or first date. In these situations, multiple factors (such as past experiences) contribute to one’s emotional state, not just a single source of arousal like an injection. Real-world emotional triggers come with a broader context and history that the study’s isolated conditions can’t capture.
  6. Experimenter bias: The experimenters knew which participants were in which condition (e.g., who received epinephrine and what information they were given about the injection). The researcher’s expectations may have influenced participants’ behavior, or the researchers could have (unintentionally) interpreted or noted behaviors in a way that aligns with their expectations.

Issues and Debates

1. Application of Psychology to Everyday Life

  • Understanding Emotions: The study demonstrates how our interpretation of physiological responses can vary based on environmental cues. This helps explain why the same physiological arousal (like a rapid heartbeat) can be labeled as excitement in one situation (e.g., before a date) and anxiety in another (e.g., before a test).
  • Decision Making: When unsure about our feelings, we often look to external factors to decide how we feel. Knowing this can aid self-awareness and introspection.

2. Individual and Situational Explanations

  • Individual: Participants had individual reactions based on their internal states and the information provided about the injection.
  • Situational: The behavior of the confederate (acting euphoric or angry) influenced participants’ interpretation of their arousal and subsequent emotional labeling.

3. Nature versus Nurture

  • Nature: The physiological response (arousal) due to the epinephrine is a biological, natural reaction.
  • Nurture: The interpretation of this arousal and the subsequent emotion felt is influenced by external, environmental factors (e.g., the behavior of the confederate and the information given about the injection).
Past Paper Questions


Dror, O. E. (2017). Deconstructing the “two factors”: The historical origins of the Schachter–Singer theory of emotions. Emotion Review9(1), 7-16.

Reisenzein, R. (1983). The Schachter theory of emotion: two decades later. Psychological Bulletin94(2), 239.

Schachter, S., & Singer, J. (1962). Cognitive, social, and physiological determinants of emotional statePsychological Review69(5), 379.

Olivia Guy-Evans, MSc

BSc (Hons) Psychology, MSc Psychology of Education

Associate Editor for Simply Psychology

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

Saul Mcleod, PhD

Educator, Researcher

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.