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Hello again Emad, On reading the last paragraph of your latest message (below), it occurred to me that you may want to look at a different line of phase perception research, namely, the perception of repeating short frequency chirps. "Up chirps" were originally designed to compensate for spatial dispersion in the cochlea and produce super clicks by coordinating neural firing across frequency in the auditory nerve. They are contrasted with "Down chirps" that increase dispersion in the cochlea. I think these chirp stimuli might help you cast your problem in terms that auditory research can help to answer. The closest paper to your interests would appear to be Uppenkamp, S., Fobel, S. and Patterson, R.D. (2001). The effects of temporal asymmetry on the detection and perception of short chirps. Hearing Research 158 71-83. Below are the abstract and the later part of the Conclusions. Regards Roy P Abstract There is an intriguing contrast between the physiological response to short frequency sweeps in the brainstem and the perception produced by these sounds. Dau et al. (2000) demonstrated that optimised chirps with increasing instantaneous frequency (up-chirps), designed to compensate for spatial dispersion along the cochlea, enhance wave V of the auditory brainstem response (ABR), by synchronising excitation of all frequency channels across the basilar membrane. Down-chirps, that is up-chirps reversed in time, increase cochlear phase delays and therefore result in a poor ABR wave V. In this study, a set of psychoacoustical experiments with up-chirps and down-chirps has been performed to investigate how these phase changes affect what we hear. The perceptual contrast is different from what was reported at the brainstem level. It is the down-chirp that sounds more compact, despite the poor synchronisation across channels and phase delays up to 20 ms. The perceived `compactness' of a sound is apparently more determined by the fine structure of excitation within each peripheral channel than by between-channel phase differences. This suggests an additional temporal integration mechanism at a higher stage of auditory processing, which effectively removes phase differences between channels. Later part of "Summary and Conclusions" (2) The differences in the BM motion produced by up-chirps and down-chirps do affect the masking period patterns that they produce. The concentrated motion produced in response to down-chirps at the start of the period is followed by deeper valleys later in the period and thus threshold is lower over a portion of the cycle. [[This means that spike order is preserved in the auditory nerve and it affects detection of click signals.]] (3) There is a big difference in the perceived sound quality of up-chirps and down-chirps. Down-chirps are perceived as more compact, or more click-like, than up-chirps. This occurs despite the synchronisation of activity across frequency channels produced by upchirps, and the extended phase delay produced by down-chirps. The sound quality of short frequency sweeps appears to reflect within-channel fine structure rather than between-channel phase differences. Time-domain models of auditory perception (Meddis and Hewitt, 1991; Patterson et al., 1992) which convert the phase-locked NAP flowing from the cochlea into an array of time-interval histograms can explain these effects, at least, qualitatively, because the time-interval calculation removes between-channel phase differences. The apparent contrast between the effect of sweep direction on the ABR and the perception of compactness suggests that the temporal integration that removes between- channel phase differences is located beyond the input to the inferior colliculus where wave V of the ABR is thought to be generated. On 08/10/2010 14:33, emad burke wrote: Dear All, -- Roy Patterson Centre for the Neural Basis of Hearing Department of Physiology, Development and Neuroscience University of Cambridge, Downing Street, Cambridge, CB2 3EG phone +44 (1223) 333819 fax 333840 email: rdp1@xxxxxxxxx http://www.pdn.cam.ac.uk/groups/cnbh/ http://www.AcousticScale.org |