Bottom-Up and Top-Down Driven Attentional Effects on Auditory Evoked Fields

Under natural environments, picking up relevant sound signals, which are embedded in other irrelevant sound signals, is an important ability for animals including humans. Bottom-up and top-down driven attention seems to play an important role in this process. In the present studies, we inves- tigated magnetic fields in humans that were evoked by pure tones embedded in band-eliminated noises during two different stimulus sequencing conditions (constant vs. random) and under two different auditory attentional conditions (focused vs. distracted) by means of magnetoencephalography. Constant stimulus sequencing was composed of identical pure tones overlaid with band-eliminated noises, whereas random sequencing was composed of pure tones of random frequencies overlaid with band-eliminated noises. We demon- strated that under focused auditory attention auditory evoked neural responses were sharper and larger in the constant se- quencing condition than the random sequencing condition. On the contrary, the auditory evoked fields under distracted audi- tory attention were larger, but not sharper in the constant sequencing condition compared to the random sequencing condition. Therefore, our results indicate that bottom-up driven audi- tory attention may mainly amplify excitatory neural networks, whereas the top-down auditory attention may both amplify and sharpen the neural activity via excitatory and inhibitory neural networks. The combination of bottom-up and top-down driven auditory attention would improve auditory performance in noisy environments.