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

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.

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.

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.

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.

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.