Subject: Re: Is there considerable phase locking up to 6 kHz? From: Roy Patterson <roy.patterson(at)MRC-CBU.CAM.AC.UK> Date: Wed, 17 Mar 2004 16:09:42 +0000At 03:37 17/03/2004 -0500, you wrote: >I think this paper is relevant to this approach. > >K. Krumbholz, R.D. Patterson, A. Nobbe, and H. Fastl. (2003). Microsecond >temporal resolution in monaural hearing without spectral cues? J. Acoust. >Soc. Am. 113 (5):2790-2800. I agree that the highpass filtered conditions are highly relevant. We have another earlier one that I think you will also find relevant. Yost, W.A., Patterson, R.D. and Sheft, S. (1998). The role of the envelope in processing iterated rippled noise. J. Acoust. Soc. Am. 104 2349-2361. Again we show evidence for the preservation of time-interval processing sufficient to make a 2AFC judgement when the stimuli are highpass filtered at 6 kHz. The place to look is in the Discussion. The relevant paragraphs are included below. I would be happy to send you a copy of the pdf if you would like. Best regards, Roy P We argue that the pitch difference between IRN stimuli generated with g=1.0 and those generated with g=-1.0 is based on waveform fine structure in frequency regions that may be as high as 6000 Hz. Frequencies in the region of 6000 Hz are above the region where phase locking is usually assumed to operate. The auditory system would need to determine the temporal structure of the IRN stimuli based on the delay (d) which is on the order of 4 to 16 ms. That is, the auditory system does not need to follow short temporal events associated with the waveform fine structure of the high-frequency IRN stimuli, but rather much longer duration regularities that are found in the IRN stimuli. Nevertheless, the ability to process even these longer temporal regularities in these very high-frequency channels appears inconsistent with the use of a lowpass filter with a 1200-Hz cutoff as a model of the loss of phase locking at high frequencies. However, such a lowpass filter is only down 30 dB at 6000 Hz. Thus, it is possible that some fine-structure information will "leak" through at these high frequencies. Such fine-structure information might be made more clear if cross-spectral processing is used. Figures 12 and 13 shows summary autocorrelograms for an IRN stimulus with d=4 ms, 8 iterations, g=1.0 (Fig. 12) and =-1.0 (Fig. 13), and a 6000- to 8000-Hz filter. These summary autocorrelograms were generated using the same modeling conditions used for Figs. 4-6, including the 1200-Hz lowpass filter to simulate the loss of phase locking. The summary correlogram is a cross-spectral processing scheme representing the sum of the autocorrelation functions of the individual channels across the 6000-8000 Hz region for each lag. As can be seen there are differences in the summary autocorrelogram between the g=1.0 and g=-1.0 conditions that might be the basis for discriminating these two stimuli. These differences in the summary autocorrelograms are much smaller for the 8000- to 1000-Hz conditions. Thus, the long-duration temporal structure that differentiates conditions when g=1.0 and from those when g=-1.0 might still exist in the processed waveform fine structure even at high frequencies, if something like a summary autocorrelogram was used as a way to extract the information. Clearly a more quantitative model is necessary to test the ability of such summary-autocorrelogram differences to account for data like those shown in Figs. 7 and 9.In this paper, we simply want to indicate that such differences in the summary autocorrelograms do exist. The work on IRN stimuli suggests that periodicities are not a necessary and sufficient condition for processing complex pitch, since there are no periodicities in the IRN waveform (see Yost et al, 1996), yet they have a clear pitch (see Yost, 1996a). Our current work suggests that the information for processing the pitch of IRN stimuli is not in the envelope. That is, the envelope by itself cannot be used to explain the discriminations between IRN stimuli generated with g=1.0 and g=-1.0. Thus, models based on either periodicity processing and/or pure envelope extraction would not be good ones for dealing with the pitch of IRN stimuli1. For instance, neural channels tuned to periodic envelope fluctuations would probably have a difficult time extracting the temporal regularity that appears to be responsible for the pitch of IRN stimuli. Any model of pitch based on envelope extraction would have to allow for fine-structure information to be available in the frequency regions below 6000 Hz. * ** *** * ** *** * ** *** * ** *** * ** *** * ** *** * ** *** * ** *** Roy D. Patterson Centre for the Neural Basis of Hearing Physiology Department, University of Cambridge Downing Street, Cambridge, CB2 3EG phone 44 (1223) 333819 office phone 44 (1223) 333837 lab fax 44 (1223) 333840 department email rdp1(at)cam.ac.uk or email roy.patterson(at)mrc-cbu.cam.ac.uk http://www.mrc-cbu.cam.ac.uk/~roy.patterson http://www.mrc-cbu.cam.ac.uk/cnbh