Janal, M. N., Clark, W. C., & Carroll, J. D. (1991). Multidimensional scaling of painful and innocuous electrocutaneous stimuli: reliability and individual differences. Perception & Psychophysics, 50(2), 108-116.
Abstract
Multidimensional scaling was used to explore whether a single intensity dimension underlies the perception of both nonpainful and painful electrical stimuli, or whether separate dimensions are required. For the scaling (INDSCAL) procedure, 41 healthy volunteers judged the similarity between all pairs of 16 intensities, which ranged from imperceptible levels to pain tolerance. For the property mapping (PREFMAP) analysis, they rated each intensity on each of 16 property scales. INDSCAL revealed four dimensions that showed high levels of both test-retest and split-half reliability. The first dimension scaled stimuli from the lowest intensity to the pain threshold. This dimension was related to property scales of sensation, affect, and arousal, but not pain, suggesting a sensory magnitude dimension. The second dimension ordered the stimuli from mildly to severely painful and was related to the painful property scale, suggesting a pain intensity dimension. Third and fourth dimensions, which refined the scaling of nonpainful stimuli, were also found. Variability in the subjects' use of the painful and nonpainful dimensions was related to their choice of stimulus descriptors. Like clinical pain, laboratory pain requires multidimensional assessment.
This study involves 41 male participants who were given electric shocks and responded to psychological tests such as the McGill Pain Questionnaire (MPQ) items.
To begin with, the Ascending method of limits (AML) was applied within which subjects were requested to respond to electric stimuli with increasing intensity with 4 V difference between steps using the following intensity scale: no sensation, slight sensation, moderate sensation, strong sensation, uncomfortable, faint pain, moderate pain and severe pain. The participants were allowed to stop the increase of electric stimuli when they consider the pain to be intolerable. The information gather through this stage is used to label the plots of the INNDSCAL results.
Participants were asked to rate the similarity between 120 pairs of stimuli with one extreme of the rating scale as "not similar" and the other end as "extremely similar". This part of the data was analyzed using the INDSCAL model.
Participants were also asked to rate eight of the stimuli intensities using 16 property scales and this part of data were analyzed using PREFMAP.
In addition, the authors ran some regression analyses to relate subject weights on different dimension to MPQ descriptors.
The authors also collected additional data from 25 of the 41 participants on a different day to reconfirm the 4 dimensional structure obtained through the INDSCAL analyses. In addition to finding similarity in the dimensional structure, high correlations of the stimuli coordinates between days were found for each of the dimensions.
In addition, the authors also calculated split-half and test-retest reliability.
Apparently, previous work had indicated the existence of independent painful and nopainful intensity dimensions. Results of this study reconfirm the existence of those two dimension and two additional nonpain dimensions.
One thing strange about this paper is that—while this is a lab study, at the very last sentence, the authors all of a sudden claimed that the model is also well suited to the study of clinical pain for no good reason… I am not quite sure whether there is some part of the writing that I am missing since this statement seemed to have come out from no where and, of course, it might have something to do with my over-drugged kind of state of mind... oops... 8-O lol sigh
This study is very much similar to the one I finished yesterday also about lab-studies on pain. Both studies speaks of the multidimensional nature of pain experiences. The paper I finished yesterday is actually a sequel of this one...
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