In situations that do not tend to provoke emotions, the average heart rate of repressors is the same as that of nonrepressors. Despite their outward calm, repressors normally feel even more excited than do nonrepressors in an emotion-provoking situation. Nonrepressors can inhibit facial and bodily displays of emotion as well as repressors do. Encountering an emotion-provoking situation is not sufficient to cause nonrepressors' heart rates to rise sharply.
Repressors -- people who unconsciously inhibit their display of emotion -- exhibit significant increases in heart rate when they encounter emotion-provoking situations. Nonrepressors have similar physiological responses when they encounter such situations and consciously inhibit their display of emotion. Thus the very act of inhibiting displays of emotion, whether done consciously or unconsciously, causes a sharp rise in heart rate.
Which one of the following is an assumption required by the argument?