Aftereffects of auditory spectral “motion”: Perceptual dissociations suggest a neural processing hierarchy

Lacherez, Philippe F. (2008). Aftereffects of auditory spectral “motion”: Perceptual dissociations suggest a neural processing hierarchy PhD Thesis, School of Psychology, The University of Queensland.

       
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Author Lacherez, Philippe F.
Thesis Title Aftereffects of auditory spectral “motion”: Perceptual dissociations suggest a neural processing hierarchy
School, Centre or Institute School of Psychology
Institution The University of Queensland
Publication date 2008-02
Thesis type PhD Thesis
Supervisor Broerse, Peter J.
Burt, Jennifer S.
Grove, Philip
Subjects 380000 Behavioural and Cognitive Sciences
Formatted abstract The motion aftereffect (MAE) is the illusory perception of motion which follows prolonged exposure to a moving visual stimulus. It is widely believed that this illusory percept reveals the underlying structure and functioning of the visual motion system. Several authors have now presented aftereffects, which have been compared to the MAE, for the perception of changing auditory pitch and have hypothesised that these aftereffects similarly may reveal something of the mechanisms of dynamic pitch perception. In one study, an aftereffect was observed for a complex noise band in which a central region was either amplified or attenuated, creating a notch or peak in the sound spectrum. If the frequency region of the notch or peak was gradually and repeatedly changed in either an upward or downward direction for a period of time, a subsequent noise band with a stationary notch or peak was heard to change pitch in the direction opposite to the previously repeated sound. In several other studies, a pure tone modulated in frequency was presented, again changing gradually and repeatedly over a period. Subsequent presentation of an unmodulated tone resulted in an illusory percept of change in the direction opposite to the repeatedly presented tone. In another study “Shepard” tones – which are ambiguous in terms of pitch – were presented in either ascending or descending musical scales. After 48 seconds of adaptation to an ascending scale, single pairs of tones in sequence tended to be heard as falling, while after a similar adaptation to a descending scale the same pairs of tones tended to be heard as ascending. It is argued in this thesis that the stimuli used in the above mentioned studies vary on a number of perceptual dimensions which may not be equivalent, and therefore may reflect several distinct aftereffects of changing pitch. The set of experiments here presented aim firstly to validate each of these aftereffects, and secondly to establish the degree of equivalence of the effects by testing whether exposure to any one of the stimuli previously used can influence the perception of the others. In Experiment 1 it is shown that the aftereffect of Shepard tones is confounded by musical context. Experiments 2, 3 and 4 examine whether there is a role of sensory adaptation in addition to musical context in the Shepard tone aftereffect by also varying the induction time, by manipulating whether individual trials are presented in an alternating fashion (ascending followed by descending) or in blocks, and by presenting the adapting and test stimuli to different ears. It is found that there is a small improvement in the effect when the induction time is changed from 3 seconds to 12-24 seconds, but no improvement when induction time was increased beyond this. The aftereffect is of the same magnitude when stimuli are presented in blocks of the same kind as when the stimuli are alternated, and equal when the induction and test occur in separate ears. It is concluded that overall there is mixed evidence for a role of adaptation in the Shepard tone aftereffect. In Experiment 5, participants were exposed to several tone types in separate conditions: Shepard tones, noise bands with moving spectral peaks, and moving spectral notches. Adaptation using spectral peaks changed the perception of moving spectral notches, but adaptation to spectral notches did not change the perception of the spectral peak stimulus. The perception of the Shepard tone stimulus did not change, nor was it changed by, the perception of the noise band stimuli. Experiments 6 and 7 examine the aftereffect for a modulating pure tone, demonstrating that it is robust, and transfers from one ear to the other, and is selective to tones in a narrow (3 octave) frequency range. In Experiment 8, participants were exposed to all four tone types (single sinusoids, spectral peaks and notches, and Shepard tones) in separate conditions. Adaptation to the pure stimulus altered the perception of spectral peaks, and to a lesser extent spectral notches. None of the other stimulus types, however, were able to affect the perception of the pure tone. It is concluded that there are not one, but three or possibly four distinct aftereffects for spectral “motion” which may reflect a hierarchy of processing in the auditory system.

 
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