Abstract
Viewing the body can influence pain perception, even when vision is non-informative about the noxious stimulus. Prior studies used either continuous pain rating scales or pain detection thresholds, which cannot distinguish whether viewing the body changes the discriminability of noxious heat intensities or merely shifts reported pain levels. In Experiment 1, participants discriminated two intensities of heat-pain stimulation. Noxious stimuli were delivered to the hand in darkness immediately after participants viewed either their own hand or a non-body object appearing in the same location. The visual condition varied randomly between trials. Discriminability of the noxious heat intensities (d′) was lower after viewing the hand than after viewing the object, indicating that viewing the hand reduced the information about stimulus intensity available within the nociceptive system. In Experiment 2, the hand and the object were presented in separate blocks of trials. Viewing the hand shifted perceived pain levels irrespective of actual stimulus intensity, biasing responses toward ‘high pain’ judgments. In Experiment 3, participants saw the noxious stimulus as it approached and touched their hand or the object. Seeing the pain-inducing event counteracted the reduction in discriminability found when viewing the hand alone. These findings show that viewing the body can affect both perceptual processing of pain and responses to pain, depending on the visual context. Many factors modulate pain; our study highlights the importance of distinguishing modulations of perceptual processing from modulations of response bias.
Highlights
Pain provides important information about the state of the body, as well as external objects that threaten the body
Using signal detection theory (Green and Swets 1966), we investigated whether viewing the body reduces the discriminability of noxious heat stimulation levels or induces a bias in perceived pain level
There was no difference in bias between hand (M = −0.01, SD = 0.30) and object (M = 0.09, SD = 0.40) conditions, t(15) = 1.22, p = .243, Cohen’s d = .283. This indicates that viewing the body reduced the discriminability of noxious stimulation levels rather than biasing pain responses (Fig. 2a)
Summary
Pain provides important information about the state of the body, as well as external objects that threaten the body. The sensation of noxious heat on the skin is an important experimental model of pain It depends on activation of nociceptive afferents that project to the brain via the spinothalamic pathway (Willis et al 1979). Noxious stimuli reduce corticospinal excitability, indicating a central inhibitory effect of pain on the motor system (Farina et al 2003; Le Pera et al 2001). These interactions between pain, innocuous sensation, and motor function may contribute to a multimodal representation of the body that facilitates responses to potentially injurious events (Haggard et al 2013)
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