Indeed, those participants that showed a stronger bias to report tactile stimulation for painful grasps also made fewer errors in action judgments in the painful grasp condition relative to the neutral grasp condition (r = 0.43, P = 0.036; Fig. 4C), indicating a close linkage between sensory tactile mapping processes and subsequent grasp judgments.
In the simulated grasp condition, participants were seated in front of a 15″ monitor, which was lying flat with the screen perpendicular to the body axis and at a distance of 45 cm under the orbitomeatal line.
This analysis was based on eight predictors, each modeling the responses to each of the eight different objects in the painful grasp condition.
Converging lines of evidence from this study support the notion that activation in the painful grasp condition reflects encoding of expected painful action consequences.
The proposal that the postcentral and IPL responses during painful grasp observation reflect SE is further supported by the finding that sensory detection thresholds were also altered in the painful grasp condition.
The largest and most robust activation was found in somatosensory cortices/IPL during the painful grasp condition compared with all other conditions, consistent with the hypothesis that these regions encode the painful consequences that emerge from actions on painful objects.
Activation in the painful grasp condition thus reflects not just a discriminative but an integrative role in action observation, with sensitivity to the consequences emerging from actions toward painful objects.
The conjunction analysis, therefore, identifies the left dorsal and ventral postcentral somatosensory cortex as the sole regions showing the features predicted for regions encoding the sensory consequences of painful hand object interactions: both the interaction of object and action factors as well as stronger responses in the painful grasp condition than in any other condition.
For the d-prime measure (Fig. 4B), there was a trend toward a main effect of action (F[1,23] = 3.6, P = 0.070), but no main effect of object and no interaction (F < 1, for both) and planned comparisons failed to reveal differences in tactile acuity between the painful grasp condition and any of the other conditions.
