How separate are the sensory, emotional, and motivational dimensions of pain? A multidimensional scaling analysis. (Clark, Janal, Hoben, & Carroll, 2001)

Clark, W. C., Janal, M. N., Hoben, E. K., & Carroll, J. D. (2001). How separate are the sensory, emotional, and motivational dimensions of pain? A multidimensional scaling analysis. Somatosensory and motor research, 18(1), 31-39.

Abstract

To map the structure of the space generated by verbal descriptors of pain, 41 male college students made pairwise similarity judgments to all possible pairings of 16 words that describe experiences commonly associated with noxious electrical stimulation. Individual Differences Scaling (INDSCAL) yielded four dimensions (D) in the group stimulus space: D-1, Intense to Moderate Experiences, contained two attributes: Strong Sensations and Strong Emotions; D-2, Moderate to Weak Experiences, exhibited two attributes: Moderate Sensations and Moderate Emotions; D-3, Motivational State, possessed two attributes: Pain and Arousal Level; D-4, Sensory Qualities, exhibited two attributes: Pain and Somatosensory Qualities. The interpretation of the dimensions was supported by Preference Mapping (PREFMAP) and by correlations between subject weights and (a) psychological tests and (b) responses to noxious electrical stimuli. Conclusion: semantically, the pain attribute or component of the total pain-suffering experience pervades emotional, motivational and somatosensory attributes. Pain is not an independent dimension. This means that a score on a pain rating scale is not a pure measure of the patient's pain, but is heavily influenced in unknown ways by the patient's emotional and motivational state.

There is been a lot of controversies concerning the dimensionality of pain. For instance, the affect theory of Marshall considers pains as merely an emotional arousal (Schneider and Karoly, 1983). On the other hand, Melzack and Casey consider pain as three-dimensional phenomena involving dimensions such as: Sensory-discriminative, motivational-affective and cognitive-evaluative.

When considering the multidimensionality of pain, another question to be addressed is whether the dimensions are independent of each other. After a review of the topic, Fernandez and Turk (1992) concluded that it is not necessary for the dimensions to be independent of each other.

Studies employing MDS or cluster analyses to investigate the dimensionality of pain have identified intensity, affect, motivation and somatosensory as the common components of pain.

• INDSCAL: The underlying assumption is that the group members shares the dimensions in the stimulus space and each individual have different weights for the different dimensions.
• PREFMAP: Using semantic anchors to assist the interpretations of the stimulus space.

The goals of the study

1. Individual Differences Scaling Model (INDSCAL) is used to assess the number of dimensions while results of PREFMAP is used to confirm the results. Validity was determined using split group comparison and test-retest reliability was also assessed.
2. Assess the relationship among the dimensions.

Methods

Subjects: no women used because the use of analgesics and ansiolytics in a later study. Test-retest reliability: 1 week apart.

Procedure

• INDSCAL:
  
• 16 descriptors
• Pair them all
• Similarity judgement on a 10 point scale
• PREFMAP
  
• Subjects rated the similarity of 16 descriptions to the 16 scales above based on a 10 point scale
• The brief Symptom Inventory (BSI)
• Participants' Attitude Toward the Study (PAT): PAT has been found to reflect the euphoric state related to the increase of endorphin after running and dysphoria related to naloxone.
• Visual analogue scale (VAS)
• Sensory Decision Theory (SDT): Participants were given electric shock and related the stimuli on a 9 point category scale ranging from No Sensation to Severe Pain.
• MPQ: Sensory, Affective and Evaluative scales were used.

Results

Results of INDSCAL analysis yielded a four-dimension structure. The indentified dimensions are Intense to Moderate Experiences, Moderate to Weak Experiences, Motivational State and Sensory Qualities.

The PREFMAP analyses confirmed the interpretation of the dimensions. Split-group analyses confirmed the validity of the results.

Test-retest reliability provides evidence for the consistency of the results. Correlations were calculated to understand the relationship between group membership and other tests of psychological traits.

This is an experimental study which gave male participants electric shocks to simulate pain. In other words, the participants weren't patients with real pain. This study employed INDSCAL to identify the dimensionality of pain. The correlations between the personal weight and a) psychological tests and b) responses to the electric shocks were used to reconfirmation of INDSCAL results. The most important finding of this study is that it supports the view of Fernandez and Turk (1992) that pain could be considered a multi-dimensional construct with the dimensions not necessarily independent of each other.