Perceptual Sensitivity to Tactile Stimuli Is Enhanced When One Is Aware That Tactile Stimulus Intensity Is Self-Controlled

Background and objectives: This study aimed to investigate whether perceptual sensitivity to tactile stimulus is affected by awareness of who controls the stimulus intensity. Methods: Thirteen healthy participants took part in this study. A participant held a dial and an experimenter held the other dial. One dial was to control the intensity of the tactile stimulus while the other (dummy dial) was inactive. The intensity of the tactile stimulus to the participant's index finger providing each 1 s was increased by the participant or by someone else with or without the participants viewing a dial controlling the stimulus intensity. Results and conclusions: The stimulus intensity at the perceptual threshold, when controlled by the participant, was significantly lower compared to when controlled by someone else, regardless of visual availability. This indicates that awareness of the self-control of the tactile stimulus intensity enhances tactile sensitivity. The electrodermal level immediately preceding the stimulus at the perceptual threshold was significantly lower when the participant controlled the stimulus intensity compared to when it was controlled by someone else, with eyes closed. The electrodermal levels immediately before the perceptual threshold stimulus, when triggered by another person, were significantly higher with the eyes closed. These electrodermal findings suggest that cognitive stress is greater when the timing of the initial tactile perception is difficult to predict.