Preattentive processing of horizontal motion, radial motion, and intensity changes of sounds.

Localization of sound sources is critical for an appropriate behavioral response. This is not only true for localization in the horizontal plane but also for localization in depth. Depth ranging of sound sources implicates various distance cues, among others sound intensity. In this study, we measured human electroencephalography and compared mismatch negativity (MMN) amplitudes and latencies for horizontal motion, radial motion, and pure intensity changes in the free field. We observed similar MMN latencies for horizontal and radial motion, whereas MMN responses to pure intensity changes were comparably delayed. MMN amplitudes and latencies were not different for approaching and receding sounds. Our data suggest similar fast processing for horizontal and radial motion, whereas pure intensity changes are possibly processed with less priority.