Odd (?) PTC data

["Brian C. J. Moore" <bcjm@xxxxxxxxx>]

Dear Ben,

With pure-tone maskers and signals, beats provide 
a powerful detection cue when the signal 
frequency is close to the masker 
frequency.    Beat detection results in elevated 
masker levels.  The added narrowband noise 
probably interfered with beat detection via the 
phenomenon of modulation detection interference 
(MDI).  Hence the masker level required to mask 
the signal became much lower.  See:

Moore, B. C. J., Alcántara, J. I., and Dau, T. 
(1998). "Masking patterns for sinusoidal and 
narrowband noise maskers," J. Acoust. Soc. Am. 104, 1023-1038.

Kluk, K., and Moore, B. C. J. (2004). "Factors 
affecting psychophysical tuning curves for 
normally hearing subjects," Hear. Res. 194, 118-134.

Best wishes,
Brian


> A few of us are reviewing a Zwicker (1974) paper 
> describing the relationship between 
> psychoacoustic and neural tuning curves. PTC?s 
> in the paper were obtained using pure tone 
> target and masking stimuli. Of interest is a 
> comparison between 2 kHz PTCs obtained in quiet 
> with the 2kHz target presented at an absolute 
> level of 31 dB SPL (Figure 1).  The masker level 
> around 2 kHz is about 45 dB SPL.
>
> A PTC at 2 kHz was also derived with an 
> additional 500 Hz narrowband noise (100 Hz BW; 
> overall level of 71 dB SPL) present (Figure 5c). 
> The level of the CF tone (2 kHz) was set to 5 dB 
> SL in this condition which happened to also be 
> 31 dB SPL (as in Figure 1). Here is the 
> confusing part (for me). The level of the pure 
> tone masker around CF in this condition was ~26 
> dB SPL or almost 20 dB less than the masker 
> level needed in quiet when the CF tone was at 31 dB SPL.
>
> In all cases the PTC?s were derived using a 
> simultaneous masking paradigm so any suppression 
> effects should be occurring on both the signal 
> and masker (as I understand it). Given the 500 
> Hz noise (71 dB SPL)  produced enough excitation 
> to shift threshold to 31 dB SPL (at 5 dB SL) 
> [Threshold for the CF tone in quiet was 6 dB 
> SPL.], why would such a lower (26 versus 45 dB 
> SPL) masker level be needed to mask the CF tone? 
> I imagine I?m missing the obvious but thought 
> I?d put this out to any interested. I?ve 
> attached the relevant pages from the Zwicker article if you are interested.
>
> Thanks,
>
> Ben Hornsby
>
>
> Zwicker, E. (1974). On a psychoacoustical 
> equivalent of tuning curves. In Facts and Models 
> in Hearing. Edited by E. Zwicker and E. 
> Terhardt. (Springer-Verlag, Berlin). pp. 132-141.

Brian C. J. Moore, Ph.D, FMedSci, FRS,
Professor of Auditory Perception,
Department of Experimental Psychology,
University of Cambridge,
Downing Street,
Cambridge CB2 3EB,
UK
Tel. +44 (0) 1223 333574
Fax. +44 (0) 1223 333564
http://hearing.psychol.cam.ac.uk