Abstract
Previous imaging studies on the brain mechanisms of spatial hearing have mainly focused on sounds varying in the horizontal plane. In this study, we compared activations in human auditory cortex (AC) and adjacent inferior parietal lobule (IPL) to sounds varying in horizontal location, distance, or space (i.e., different rooms). In order to investigate both stimulus-dependent and task-dependent activations, these sounds were presented during visual discrimination, auditory discrimination, and auditory 2-back memory tasks. Consistent with previous studies, activations in AC were modulated by the auditory tasks. During both auditory and visual tasks, activations in AC were stronger to sounds varying in horizontal location than along other feature dimensions. However, in IPL, this enhancement was detected only during auditory tasks. Based on these results, we argue that IPL is not primarily involved in stimulus-level spatial analysis but that it may represent such information for more general processing when relevant to an active auditory task.
Highlights
The spatial location of a sound source is not directly mapped along the sensory epithelium but must be computed based on various binaural cues
The difference is consistent with the fact that successful discrimination requires perception of both sounds in a pair, whereas the stimulus identity of the first sound could suffice in the 2-back task
In discrimination tasks, reaction times (RTs) was slower when the task was performed on SL than on SD (t = 2.6, P < 0.05) or on SR (t = 2.6, P < 0.05) sounds, whereas there were no significant differences between the stimulus conditions in 2-back tasks
Summary
The spatial location of a sound source is not directly mapped along the sensory epithelium but must be computed based on various binaural cues. These cues result from differences in the level and arrival time of sound at the two ears, spectral cues resulting from direction-dependent filtering of sound by the head, outer ears and torso, overall intensity, and echoes in a reverberant environment. In particular, are important for localizing the sound source in horizontal plane. We compared activations in human auditory cortex (AC; Woods et al, 2010) to sounds emitted by sources at different horizontal locations, at different distances, or in different rooms. We used naturalistic and carefully controlled sounds recorded in realistic acoustical spaces, as the different spatial cues are not processed independent of each other in natural listening conditions
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