Sound localization difficulty affects early and late processing of auditory spatial information: investigation using the dipole tracing method.

OBJECTIVE: To understand the functional roles of brain regions related in the auditory spatial localization, we recorded auditory event-related potentials (ERPs) and estimated their source generators using the dipole tracing method. METHODS: Target sound stimuli perceived as coming from two directions (-90 degrees, +90 degrees where 0 degrees was straight behind the subject within the azimuth in the interaural plane) were randomly presented with two distracter stimuli for providing difficulty of detection. The distracter stimuli were 75 degrees behind the target stimuli (easy task) and 45 degrees behind the target stimuli (difficult task). RESULTS: Compared with the passive listening tasks, distinct potentials appeared in the easy task at the early (110-150 ms: N1-late) time windows of ERPs and in the difficult task at the late (450-800 ms: slow wave, SW) time windows of ERPs. Dipoles were estimated to be at the posterior auditory cortex, precuneus and thalamus for N1-late, and the middle/inferior frontal gyrus, anterior region of superior temporal gyrus and parahippocampal gyrus for SW for both tasks. CONCLUSIONS: Difficulty of sound localization may affect brain function related to analyzing features of the spatial cue, eventually identifying the spatial location, and attention. SIGNIFICANCE: Brain regions responsible for sound localization may show different activity patterns depending on the functional roles of each brain region.