19 December 2004

Effects of exposure on perception of pain expression

Effects of exposure on perception of pain expression
Prkachin, et. al

I don't normally quote this much from an article, but this one is interesting. Take note my simulation friends.
When a sufferer displays pain, the responses of others can vary. Common affective responses may be sympathy and empathy, but they can include fear, or even pleasure in the other's suffering. Behaviorally, observers often provide assistance or seek ways to soothe the other's suffering; however, they may also criticize, note the evidence of suffering but say nothing or not notice at all. All but the last alternative presupposes that the observer has engaged in some perceptual processing of the event (Prkachin and Craig, 1994). Differences in these responses may affect the sufferer. For example, there is evidence that health-care practitioners underestimate the suffering of pain patients ( Marquié et al., 2003). Such ‘miscalibration’ can affect treatment decisions, thereby influencing the individual's quality of life. Likewise, operant theorists suggest that the manner in which others respond to evidence of pain can set the stage for chronic pain or stoicism ( Fordyce, 1976).

The study of judgments of facial expressions of pain offers a way to understand the perception of the suffering of others. Facial expressions provide evidence about pain that is valid (Craig et al., 2001) and graded in intensity ( Prkachin, 1992 and Prkachin and Mercer, 1989). Observers are sensitive to the information contained in the display ( Prkachin and Craig, 1985 and Prkachin et al., 1994); however, there are marked individual differences in their judgments. Some of these differences may be attributable to experience. For example, Prkachin et al. (2001) studied how people with different experience perceived shoulder-pain patients' facial expressions. Observers generally underestimated pain (relative to the ratings of the sufferers themselves). Compared with people who had little experience with pain patients, health-care workers showed greater underestimation. Relatives of pain patients showed less.


There is also evidence that certain types of experience alter participants' decisional biases about pain expression. Prkachin et al. (1983) showed that providing observers with information that others should be hypersensitive to pain increased their general tendency to impute pain. Lundquist et al. (2002) showed that information that a person being judged was behaving in accordance with medical advice led judges to impute greater pain.

In the present study, we were interested in whether we could adduce evidence for selective adaptation to pain expression. We hypothesized that increasing exposure to pain expression would be associated with reduced sensitivity. Signal detection methodology was employed in order to map effects on perceptual sensitivity and decisional bias.


The expectation that selective adaptation to pain expression by overexposure would result in diminished sensitivity to pain expression was not supported. Instead, high levels of exposure were associated with significant alterations in observers' criteria for indicating that a particular expression showed pain. With increasing exposure to displays of strong pain, false alarm and hit probabilities decreased in a parallel fashion, indicating that observers became more conservative in their pain judgments. To our knowledge, this is the first experimental demonstration of a quantitative shift in criteria for judging pain expression. The findings provide evidence of an adaptation-level effect (Helson, 1964 and Rollman, 1979) in the judgment of pain expression. Adaptation-level refers to the observation that, in psychophysical judgment tasks, the evaluation that an observer makes of a stimulus may depend on the context in which judgments are made. Rollman (1979), for example, demonstrated that judgments of the amount of pain induced by electric shocks were influenced by the level of comparative shocks presented at the same time. When a relatively weak stimulus was judged in the presence of a weaker stimulus, participants gave higher ratings than they gave to stronger stimuli judged in the context of even stronger stimuli. In the present study, participants were less willing to judge moderately painful expressions as painful when they had been exposed to a large number of even more painful expressions than when they had been exposed to a relatively smaller number. The significant linear reduction in false alarm and hit rates was suggestive of a ‘dose-dependent’ relationship.

This unexpected finding may bear on the observation that, relative to people with little experience with pain sufferers, health practitioners who routinely deal with pain patients provide lower judgments of the magnitude of pain when relying on the same behavioral information (Prkachin et al., 2001). There are a variety of possible interpretations of this difference, including divided attention, cognitive differences attendant on training and differential experience. The present findings suggest a relatively parsimonious interpretation of the effect. If one is exposed to evidence of considerable pain in relatively large amounts and if an adaptation-level effect is operative, then high-intensity expression may become the standard against which pain in others is evaluated, and other expressions will be ‘downgraded’ accordingly.

The second finding of note was that female observers were better able to detect the presence of pain expression than men. Though novel to the pain expression field, there is a literature that documents female superiority in decoding nonverbal cues (Brody, 1985 and Hall, 1978). The present study is consistent with that literature, which notes a particular advantage for females in decoding cues of negative emotional states. Though significant, the implications of the difference documented in the present study may be limited due to the fact that the effect size was quite small. Nevertheless, in circumstances in which it may be desirable to select individuals who decode pain expression well, such as in decoding studies or pain assessment, there may be an advantage in selecting females.

A third finding that warrants emphasis is the high level of acuity displayed by participants, regardless of experimental condition. Average values of the discriminability measure varied from 0.91 to 0.94 on an index on which a value of 1.0 indicates perfect performance. These levels of performance appear quite impressive when considered in relation to the facts that the test stimuli displayed facial behavior categorized as moderate in intensity and they were displayed for only 1 s. Clearly, under the conditions maintained in the present study, people are highly sensitive to changes in facial behavior indicative of pain. This degree of acuity appears likely to reflect the kind of non-conscious automatic activation of evaluative processes (such as trait judgments) that characterizes the perception of complex social behaviors, (Bargh and Ferguson, 2000). No doubt this speaks to the adaptive nature of sensitivity to pain expression, an ability that is likely to contribute to the fitness of both the sufferer and the observer ( Fridlund, 1994 and Williams, 2002)

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