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On the auditory adaption aftereffects Dong, Charles Chang-Jiang

Abstract

In this thesis, selective adaptation experiments are presented which investigate motion detection and signal processing in the human auditory system. The existence of a motion aftereffect is often regarded as evidence for the existence of specialized motion sensitive mechanisms in a modality. Using real moving sounds as both the adapting and test stimuli, a robust and reliable simple auditory motion aftereffect (aMAE) was observed in all of seven subjects tested. After listening to a sound source moving repeatedly in one direction (right or left), a stationary sound source was perceived to move in the opposite direction. The size of the aMAE increased with adapting velocity up to the highest velocity tested (20°/sec). Its strength depended on matching both the spatial location and frequency content of the adapting and test stimuli, suggesting that the aMAE is both spatially and frequency specific. The studies of auditory adaptation were extended to studies of auditory contingent motion aftereffects. In the visual system, many types of contingent aftereffect have been demonstrated since the discovery of the McCollough effect. Although the basis of this aftereffect remains unclear, it is believed to reflect some fundamental aspects of learning and sensory coding. By pairing the directions of sound movement in frequency and in azimuth, the presence of a contingent aftereffect was demonstrated for the first time in the auditory system. This spectral contingent spatial motion aftereffect can persist for four hours after adaptation. The existence of the contingent aftereffect in audition was further confirmed by demonstration of an intensity contingent spectral aftereffect. Since sound motion in azimuth (A) can be made contingent on sound motion in frequency (B), which in turn can be contingent on motion in intensity (C), the possibility of attribute A being made contingent on attribute C by way of attribute B was explored. No such "double" contingent aftereffect was obtained. These results imply that the neural mechanisms underlying contingent aftereffects are not specific to vision, but reflect general properties of sensory neural processing. The long time course of contingent aftereffects suggests that they may be related to cortex-based learning processes

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