Painful decisions: How classifying sensations can change the experience of pain

Background: Categorizing perceptual stimuli is a mechanism for
facilitating the processing of sensory input from our environment. This
facilitation of perception is achieved through generalization
(assimilation) of stimulus characteristics within categories and
accentuation between categories. These categorization processes have
been demonstrated in visual, auditory, tactile and social perception, but
never in pain perception.
Method: We presented participants with six thermal noxious stimuli,
increasing in steps of 0.5 °C. In an experimental group, stimuli were
assigned to two categories labelled A and B containing the three lower
(A1, A2, A3) and three higher (B1, B2, B3) stimuli. A control group did
not receive such category information (stimuli were labelled S1–S6). In
a first part of the experiment, participants simply rated pain intensity
and unpleasantness for all stimuli. In a second part, we presented
stimuli without labels and participants had to identify the label of each
stimulus.
Results: We found evidence for categorization effects in both pain
ratings and stimulus identification data. In particular, unpleasantness
ratings within categories were more similar to each other, and ratings
between categories less similar, in the experimental compared to control
group. Participants in the experimental group also confused stimuli
more often within than between categories, and were more confident
about category membership of stimuli at the category border, compared
to participants in the control group.
Conclusions: Mere category information, using abstract category labels,
significantly changes pain perception. Implications for our understanding
of cognitive pain modulation mechanisms, as well as clinical
implications of categorization effects are discussed.
Significance: Categorization effects in pain perception are demonstrated.
Classifying and labelling painful events can modulate early perceptual
processes, lead to under- or overestimation of pain symptoms and affect
decision-making behaviour related to pain.