Figure 1.
Rubber hands used in the experiments.
We used 4 rubber hands that represented the following conditions: (a) did not evoke a negative body image, (b) evoked a pain-related negative body image, (c) evoked a negative body image due to non-conformance of a socially accepted appearance, and (d) evoked a negative body image due to non-conformance of the concept of a normal body.
Figure 2.
Experimental setting for pain threshold measurement.
A thermal probe was placed on the participant's forearm and a fake thermal probe was placed on the forearm of the rubber hand. The participant was instructed to stare at the rubber hand during the pain threshold measurement. The experimenter increased the temperature of the stimulus by 1°C per second. The participant used a remote control in his/her right hand to stop the temperature from increasing any further the moment pain was felt. The temperature was recorded as the pain threshold.
Figure 3.
The experiment consisted of 4 sequences of experimental steps for each of the 8 conditions presented by the rubber hands. Each sequence was designed to include an index finger location task, pain threshold measurement, a rubber hand illusion questionnaire, and unpleasantness rating.
Table 1.
Value of drift (SE), subjective degree of illusion (SE), and pain threshold (SE) under each condition.
Figure 4.
Value of drift (a) and subjective degree of illusion (b) under each condition.
The post-hoc test showed that the value of drift and perceived effectiveness of the illusion under the distorted condition were significantly lower than under the normal, injured, and hairy conditions. Error bars indicate ± SE. * p<0.005.
Figure 5.
Unpleasantness associated with embarrassment, injury and nonconformance (NRS) under each condition.
The post-hoc test showed that the hairy condition had a significantly greater impact than the normal, injured and distorted conditions for the item of unpleasantness associated with embarrassment. The post-hoc test showed that the injured condition had a significantly greater impact than normal, hairy and distorted conditions for the item of unpleasantness associated with injury while the hairy condition had a significantly greater impact than normal, injured and distorted conditions for unpleasantness associated with embarrassment. Error bars indicate ± SE. * p<0.0083.
Figure 6.
Pain threshold under each condition.
The arm pain threshold was significantly lower under the injured condition than for the normal, hairy, and distorted conditions. Error bars indicate ± SE. * p<0.005.