Remijn & Kojima – Auditory Streaming and Nirs

We used near-infrared spectroscopy (NIRS) to assess listeners’ cortical responses to a 10-s series of pure tones separated in frequency. Listeners were instructed to either judge the rhythm of these “streaming” stimuli (active-response listening) or to listen to the stimuli passively. Experiment 1 showed that active-response listening caused increases in oxygenated hemoglobin (oxy-Hb) in response to all stimuli, generally over the (pre)motor cortices. The oxy-Hb increases were significantly larger over the right hemisphere than over the left for the final 5 s of the stimulus. Hemodynamic levels did not vary with changes in the frequency separation between the tones and corresponding changes in perceived rhythm (“gallop”, “streaming” or “ambiguous”). Experiment 2 showed that hemodynamic levels were strongly influenced by listening mode. For the majority of time windows, active-response listening caused significantly larger oxy-Hb increases than passive listening, significantly over the left hemisphere during the stimulus and over both hemispheres after the stimulus. This difference cannot be attributed to physical motor activity and preparation related to button-pressing after stimulus end, because this was required in both listening modes. Remijn & Kojima – Auditory streaming and NIRS 3