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.
Zwicker, E. (1974). On a psychoacoustical equivalent of
tuning curves. In Facts and Models in Hearing. Edited by E. Zwicker and
Zwicker 1974 Fig1 and 5.pdf
Description: Zwicker 1974 Fig1 and 5.pdf