Somatosensory influence on auditory cortical response of self-generated sound

Motor execution which results in the generation of sounds attenuates the cortical response to these self-generated sounds. This attenuation has been explained as a result of motor relevant processing. The current study shows that corresponding somatosensory inputs can also change the auditory processing of a self-generated sound. We recorded auditory event-related potentials (ERP) in response to self-generated sounds and assessed how the amount of auditory attenuation changed according to the somatosensory inputs. The sound stimuli were generated by a finger movement that pressed on a virtual object, which was produced by a haptic robotic device. Somatosensory inputs were modulated by changing the stiffness of this virtual object (low and high) in an unpredictable manner. For comparison purposes, we carried out the same test with a computer keyboard, which is conventionally used to induce the auditory attenuation of self-generated sound. While N1 and P2 attenuations were clearly induced in the control condition with the keyboard as has been observed in previous studies, when using the robotic device the amplitude of N1 was found to vary according to the stiffness of the virtual object. The amplitude of N1 in the low stiffness condition was similar to that found using the keyboard for the same condition but not in the high stiffness condition. In addition, P2 attenuation did not differ between stiffness conditions. The waveforms of auditory ERP after 200 ms also differed according to the stiffness conditions. The estimated source of N1 attenuation was located in the right parietal area. These results suggest that somatosensory inputs during movement can modify the auditory processing of self-generated sound. The auditory processing of self-generated sound may represent self-referenced processing like an embodied process or an action-perception mechanism.