Effect of attention on cortical processing of sound motion: an EEG study

The onset of motion in an otherwise continuous sound elicits a prominent auditory evoked potential, the so-called motion onset response (MOR). The MOR has recently been shown to be modulated by stimulus-dependent factors, such as velocity, while the possible role of task-dependent factors has remained unclear. Here, the effect of spatial attention on the MOR was investigated in 19 listeners. In each trial, the subject initially heard a free-field sound, consisting of a stationary period and a subsequent period of motion. Then, two successive stationary test tones were presented that differed in location and pitch. Subjects either judged whether or not the starting and final positions of the preceded motion matched the positions of the two test tones ('motion-focused condition'), or whether or not the test tones were identical in pitch, irrespective of the preceded motion stimulus ('baseline condition'). These two tasks were presented in separate experimental blocks. The performance level in both tasks was similar. However, especially later portions of the MOR were significantly increased in amplitude when auditory motion was task-relevant. Cortical source localization indicated that this extra activation originated in dorsofrontal areas that have been proposed to be part of the dorsal auditory processing stream. These results support the assumption that auditory motion processing is based on a complex interaction of both stimulus-specific and attentional processes.