Brain activity during auditory backward and simultaneous masking tasks.

Normal-hearing adult subjects performed a simultaneous and a backward auditory masking task, while their brain activity was recorded using functional magnetic resonance imaging. No differences between these tasks were observed in the auditory brain regions on the superior temporal lobes. Brain activity was larger for simultaneous than backward masking in the left inferior parietal lobe, the left inferior frontal cortex, the posterior cingulate cortex, and the cerebellum. In contrast, backward masking gave more activation in the left and right anterior temporal poles, and the anterior cingulate cortex. Apparently, backward and simultaneous masking tasks activate different auditory processing streams and require different cognitive brain resources.