Automatic cortical responses to sound movement: a magnetoencephalography study

The aim of the present study was to clarify what change detection process leads to the elicitation of the auditory change-sensitive N1ms using magnetoencephalography (MEG). We brought our attention to whether these N1ms would be elicited if physical changes to the stimulus are eliminated. For this purpose, sound movement (SM), which entails a very subtle change only to the manner of stimuli presentation, was used in the present study. SM presentation was achieved by inserting an interaural time difference to one ear. The results indicate that both SM and the onset of the control stimulus (ON) elicited MEG responses at the superior temporal gyrus (STG) of both hemispheres. ON-N1m peak latencies were significantly shorter than those of SM-N1m as well. Interestingly, the pre-event (ON or SM) length (PreEL) was a significant factor determining the amplitude of the STG activity. Due to these findings, we hypothesize that both ON and SM activate similar groups of neurons or even an identical group of neurons. In addition, since correlations between PreEL and ON/SM-N1m amplitude exist, it is suggestible that N1m is not merely a nonspecific automatic response to physical change, but rather a much more sophisticated change-sensitive response employing a memory mechanism.