Sensorial suppression of self-generated sounds and its dependence on attention.

The auditory processing of self-generated sounds is characterized by an attenuated vertex N1-component of the event-related potential (ERP) compared to the responses elicited by externally generated sounds. Typically, a motor condition where sounds are actively produced by button presses is compared with a passive listening condition. While this effect is usually interpreted as reflection of an internal forward model system, the impact of attention and arousal on the so called self-generation effect has not been systematically controlled in these studies: Is the auditory stimulation more attended during the active task compared to passive listening, e.g., caused by a higher arousal level? Or is it rather attended less and attention is drawn away from the task-irrelevant stimulation to the motor task? Accordingly, the self-generation effects reported in the literature can easily be over- or underestimated. In the present study we disentangled attention from the self-generation effect by introducing an active listening condition, in which attention is focused to the same feature as in the self-generation condition - the stimulus onset-to-onset interval. We observed a classical 'self-generation effect', i.e. attenuated amplitudes for self-generated compared to passive listened sounds at frontocentral electrodes. As expected this effect was overlapped by attention effects in space and time. However, topographical and tomographical analyses allowed us to clearly disentangle both effects. Our results argue for the existence of a genuine self-generation effect, but emphasize the problem of possible over- or underestimation caused by attentional confounds.