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UBC Theses and Dissertations

Facial action determinants of pain judgment Lee, Douglas Spencer


Nonverbal indices of pain are some of the least researched sources of data for assessing pain. The extensive literature on the communicative functions of nonverbal facial expressions suggests that there is potentially much information to be gained in studying facial expressions associated with pain. Results from two studies support the position that facial expressions related to pain may indeed be a source of information for pain assessment. A review of the literature found several studies indicating that judges could make discriminations amongst levels of discomfort from viewing a person's facial expressions. Other studies found that the occurrence of a small set of facial movements could be used to discriminate amongst several levels of self-reported discomfort. However, there was no research directly addressing the question of whether judges ratings would vary in response to different patterns of the identified facial movements. Issues regarding the facial cues used by naive judges in making ratings of another person's discomfort were investigated. Four hypotheses were developed. From prior research using the Facial Action Coding System (FACS) (Ekman S. Friesen, 1978) a small set of facial muscle movements, termed Action Units (AUs), were found to be the best facial movements for discriminating amongst different levels of pain. The first hypothesis was that increasing the number of AUs per expression would lead to increased ratings of discomfort. The second hypothesis was that video segments with the AUs portrayed simultaneously would be rated higher than segments with the same AUs portrayed in a sequential configuration. Four encoders portrayed all configurations. The configurations were randomly editted onto video tape and presented to the judges. The judges used the scale of affective discomfort developed by Gracely, McGrath, and Dubner (1978). Twenty-five male and 25 female university students volunteered as judges. The results supported both hypotheses. Increasing the number of AUs per expression led to a sharp rise in judges' ratings. Video segments of overlapping AU configurations were rated higher than segments with non-averlapping configurations. Female judges always rated higher than male judges. The second study was methodologically similar to the first study. The major hypothesis was that expressions with only upper face AUs would be rated as more often indicating attempts to hide an expression than lower face expressions. This study contained a subset of expressions that were identical to ones used in the first study. This allowed for testing of the fourth hypothesis which stated that the ratings of this subset of expressions would differ between the studies due to the differences in the judgment conditions. Both hypotheses were again supported. Upper face expressions were more often judged as portraying attempts by the encoders to hide their expressions. Analysis of the fourth hypothesis revealed that the expressions were rated higher in study 2 than study 1. A sex of judge X judgment condition interaction indicated that females rated higher in study 1 but males rated higher in study 2. The results from these studies indicated that the nonverbal communication of facial expressions of pain was defined by a number of parameters which led judges to alter their ratings depending on the parameters of the facial expressions being viewed. While studies of the micro-behavioral aspects of facial expressions are new, the present studies suggest that such research is integral to understanding the complex communication functions of nonverbal facial expressions.

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