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The IPD circle – a two-dimensional representation of interaural temporal differences in stimulus fine structure

Marquardt, T.; (2012) The IPD circle – a two-dimensional representation of interaural temporal differences in stimulus fine structure. Doctoral thesis, UCL (University College London).

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Abstract

The ability of binaurally-sensitive neurons to detect microsecond differences in interaural timing challenges the temporal processing capacity of the nervous system. Whilst brain mechanisms responsible for such exquisite processing have been investigated for 6 decades, it would be fair to say that this field has undergone something of a revolution in the last ten years, with. This study reviews new findings challenging long standing models and assumptions. Particular emphasis is put on the asymmetry of many neural tuning curves to the interaural time delay of wideband stimuli around their maximum, which implies that such external temporal differences are compensated by some internal phase-delay mechanism rather than a system of axonal time delays as is the prevailing notion today. Such internal phase delay explains why the ITD that generates maximum neural activity is generally found to be less than a half period of the tuning curve’s modulation (p-limit). The study proposed the interaural phase circle (IPD circle) and the smoothed interaural phase spectrum (SIPS) as new binaural displays, which are based on these physiological findings. The IPD-circle displays the interaural phase difference and the interaural phase coherence within a single frequency channel in a polar diagram as vector angle and magnitude, respectively. Its two-dimensionality facilitates the study of IPD and IPC fluctuations. The SIPS shows an activation matrix of binaural coincidence detectors across their best frequencies and internal phase delays. It serves similarly to the traditional crosscorrelogram as a display of interaural temporal differences across frequency. Its computation is based on the interaural phase spectrum, which is smoothed in the frequency-dimension by the auditory filter shapes. Both displays describe neural ITD tuning curves with their asymmetry, and could provide a basis for future physiologically orientated models.

Type:Thesis (Doctoral)
Title:The IPD circle – a two-dimensional representation of interaural temporal differences in stimulus fine structure
Language:English
Additional information:Permission for digitisation not received
UCL classification:UCL > School of Life and Medical Sciences > Faculty of Brain Sciences > Ear Institute

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