Investigating low-frequency compression using the Grid method

There is an ongoing discussion about whether the amount of cochlear compression in humans at low frequencies (below 1 kHz) is as high as that at higher frequencies. It is controversial whether the compression affects the slope of the off-frequency forward masking curves at those frequencies. Here, the Grid method with a 2-interval 1-up 3-down tracking rule was applied to estimate forward masking curves at two characteristic frequencies: 500 Hz and 4000 Hz.

The resulting curves and the corresponding basilar membrane input-output (BM I/O) functions were found to be comparable to those reported in literature. Moreover, slopes of the low-level portions of the BM I/O functions estimated at 500 Hz were examined, to determine whether the 500-Hz off-frequency forward masking curves were affected by compression.

Overall, the collected data showed a trend confirming the compressive behaviour. However, the analysis was complicated by unexpectedly steep portions of the collected on- and offfrequency forward masking curves.