Both Darwin (1872) and James (1884) have suggested that the experience of an emotion is at least partly a product of the facial changes that occur during an emotion episode. Modern counterparts of these ideas have been encapsulated in the facial feedback hypothesis (e.g., Laird, 1974; McIntosh, 1996). Winton (1986) identified two versions of the facial feedback hypothesis. In the categorical version, adopting the facial expression associated with a particular emotion enhances the experience of that emotion and that emotion only. In the dimensional model, facial expressions affect a single emotion-related dimension, probably that of pleasantness-unpleasantness. Much of the existing research has been unable to distinguish between these two approaches, because participants are most usually required to only adopt one positive and one negative facial expression. The arguments for and against the facial feedback hypothesis are many and complex and are somewhat reminiscent of the debates we reviewed in Chapter 3 concerning the evidence for universal facial expressions corresponding to basic emotions. While having no wish to oversimplify the issues, we will restrict ourselves to the suggestion that the evidence for some form of facial feedback that enhances the individual's experience of emotions is, in our view, persuasive. Let us consider one example in support of this claim. Duclos et al. (1989) carried out a series of two experiments examining Winton's categorical version of the facial feedback hypothesis. In Experiment 1, participants had to adopt facial expressions related to fear, anger, disgust, and sadness. The participants were informed that the facial expressions were part of a study looking at brain lateralisation, and were not explicitly informed that they were emotion-related. The participants then had to complete emotion rating scales and the results indicated that each expression increased the self-reported experience of the corresponding emotion significantly, over and above at least two of the other expression conditions.
If the evidence in support of the facial feedback hypothesis does stand up to scrutiny, the question is then raised as to what mechanism underlies feedback. Zajonc, Murphy, and Inglehart (1989), in their vascular theory of emotional efference (VTEE), have suggested that facial muscular movement, via its action on the cavernous sinus, restricts venous flow and thereby influences the cooling of the arterial blood supply to the brain. Independent studies suggest that such cooling produces changes in the phenomenal experience of emotions. Such theories are clearly speculative and the jury is still out on the mechanism that facial feedback might use. However, in the first case report of a patient with the very rare condition of bilateral facial paralysis in which there is no feedback from the facial musculature, Keillor, Barrett, Crucian, Kortenkamp, and Heilman (2002) found that the patient reported no diminution of emotional experience or discrimination of facial emotional expressions. This research would suggest a more limited contribution than initially proposed by the hypothesis.
In addition to the research looking at facial feedback, there are several studies that have examined the effects of posture on the experience of emotion (Duclos et al., 1989; Riskind, 1984; Riskind & Gotay, 1982). Work in this area is still very preliminary; however, there does appear to be some evidence to suggest that posture has a weaker effect than facial feedback but it can influence or mediate an individual's experience of emotions (Flack, 2006).
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