1. Two-factor theory of emotions
The experiment of Schachter and Singer (1962):
Gregorio Marañon (1924) found that participants did not experience a genuine emotion after injection of epinephrine.
There was one exception: If participants were asked to imagine how their parents die or how their children get ill, participants felt a genuine emotion, but only if this instruction was given after the injection of epinephrine. If it was given before, no effect could be observed.
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2. Two-factor theory of emotions
This led several authors to postulate a two-factor theory of emotions, assuming that an emotion is determined by two factors:
Unspecific physiological activation. This is a necessary, but not sufficient condition to elicit an emotion.
Cognitive interpretation of the situation determines the quality of an emotion.
Stanley Schachter and Jerome Singer tested the two-factor theory in a now classical study. The logic behind their experiment was the following:
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3. Experiment of Schachter and Singer
If there exists physiological arousal for which there is no explanation:  Quality of emotion depends on cognitive interpretation. The same state of physiological arousal can be experienced as either joy or anger.
If physiological arousal can be explained:  No emotion.
Identical cognitive interpretations elicit an emotion only if there is physiological arousal.
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4. Experiment of Schachter and Singer
Hypotheses:
Epinephrine P
Placebo A
Informed A
Not informed A
Misinformed
Euphoria
Anger
Euphoria
Neutral
Anger
Neutral
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5. Experiment of Schachter and Singer
Results: Self report
Epinephrine P
Placebo A
Informed A
Not informed A
Misinformed
Euphoria
1.61
1.78
1.90
0.98
In both conditions: The higher number denotes more positive emotions
Anger
1.39
1.91
1.63
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6. Experiment of Schachter and Singer
Results: Behavior
Epinephrine P
Placebo A
Informed A
Not informed A
Misinformed
Euphoria
16.00
18.28
22.56
12.72
Euphoria The higher, the more euphoria
Anger: The higher, the more anger
Anger
2.28
-0.18
0.79
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7. Experiment of Schachter and Singer
Conclusion:
The hypotheses of the two-factor theory of emotions were only partly confirmed, and some other studies did not provide support for or even contracdicted the two-factor theory of emotion (Lazarus et al., 1965; Maslach, 1979; Marshall & Zimbardo, 1979).
However, this study stimulated many other experiments on the role of arousal and cognitive appraisal of the situation (e.g., Dutton & Aron, 1974; Zillmann et al., 1972)
Results: Behavior
Epinephrine P
Placebo A
Informed A
Not informed A
Misinformed
Euphoria
16.00
12.72
18.28
22.56
Euphoria The higher, the more euphoria
Anger: The higher, the more anger
Anger
0.79
-0.18
2.28
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