sets of facial expression and asking subjects to relive a

 past emotional experience produced similar autonomic

 changes, i.e., increases in HR and SCR (Ekman, Levenson, &

 Friesen, 1983; Levenson, Ekman, and Friesen, 1990). These

 authors concluded that there are biologically innate affect

 programs which, when activated, provide instructions to

 multiple response systems including skeletal muscles,

 facial muscles, and the autonomic nervous system.

 Taken together, the above research suggests that

 zygomatic EMG increases with reported pleasantness, and

 somewhat with extreme unpleasantness. Corrugator EMG

 increases with reported unpleasantness. Skin conductance

 responses are positively related to reported experience of

 arousal, which can be induced through pleasant or unpleasant

 emotional states. Heart rate, however, is variable and

 depends on many factors such as reported affect, type of

 evoking stimuli, and individual differences in responding.

 However, during the presentation of emotional slides, HR

 acceleration is positively related to valence, but

 acceleration may be associated with aversive rather than

 pleasant stimuli when phobics are presented with their fear

 object. During imagery, HR typically accelerates during

 both pleasant and unpleasant scenes. Additionally,

voluntary facial expressions produce changes in the

autonomic nervous system consistent with other tasks used to

induce emotional experience.