Viewing needle pricks enhances unpleasantness ratings and pupil dilation responses to concurrent painful and nonpainful stimuli. Situational expectations about needle pricks primarily affect intensity ratings.
“Don’t look and it won’t hurt” is commonly heard advice when receiving an injection, which implies that observing needle pricks enhances pain perception. Throughout our lives, we repeatedly learn that sharp objects cause pain when penetrating our skin, but situational expectations, like information given by the clinician prior to an injection, may also influence how viewing needle pricks affects forthcoming pain. How both previous experiences and acute situational expectations related to viewing needle pricks modulate pain perception is unknown. We presented participants with video clips of a hand perceived as their own being either pricked by a needle or touched by a Q-tip, while concurrently applying painful or nonpainful electrical stimuli. Intensity and unpleasantness ratings, as well as pupil dilation responses, were monitored. Effects of situational expectations about the strength of electrical stimuli were investigated by manipulating the contingency between clips and electrical stimuli across experimental blocks. Participants were explicitly informed about the contingency. Intensity ratings of electrical stimuli were higher when a clip was associated with expectation of painful compared to nonpainful stimuli, suggesting that situational expectations about forthcoming pain bias perceived intensity. Unpleasantness ratings and pupil dilation responses were higher when participants viewed a needle prick, compared to when they viewed a Q-tip touch, suggesting that previous experiences with viewing needle pricks primarily act upon perceived unpleasantness. Thus, remote painful experiences with viewing needle pricks, together with information given prior to an injection, differentially shape the impact of viewing a needle prick on pain perception.