Auditory Perception and Cognition
Stephen McAdams, Carolyn Drake
Stevens' Handbook of Experimental Psychology
A. Auditory filter shapes at low frequencies We recently established two important findings on frequency tuning in the human inner ear. First, tuning was sharper than previously thought, and sharpened considerably with increasing frequency from 1000 to 8000 Hz; second, human tuning was sharper by a factor of two than that found in other mammals that are often used as models of human hearing (Shera, Guinan & Oxenham, 2002; PNAS 99:3318-23). The technique used that in that study was suitable only
... for frequencies at and above 1000 Hz. Important speech information is carried at lower frequencies, particularly when the speech is mixed with interfering sources. We have therefore developed a behavioral technique that allows us to estimate human filter shapes at lower frequencies. We find that the divergence between our new measures and the earlier estimates of filter tuning are less at low than at high frequencies and we are now in the position to provide a complete estimate of low-level human cochlear filter tuning from 250 Hz to 8000 Hz. B. Changes in cochlear tuning with level It has been known since the early days of hearing research that the auditory system has many nonlinearities. One of the most well-known is the deterioration of cochlear tuning at high levels. It remains unknown how much of the deterioration in tuning is because of a broadening of the response area of individual primary auditory neurons (or places along the basilar membrane), and how much is because of nonlinear suppression effects that can strongly affect behavioral tuning estimates when the masker and probe are presented at the same time. We have addressed this issue by using non-simultaneous masking to measure cochlear tuning as a function of the probe frequency. We find that tuning is strongly level dependent at higher signal frequency of 4000 Hz and above, but essentially independent of level for low and medium stimulation levels at 1000 Hz. The results, along with those of Sect. 1A, provide important new data and constraints for computational models of human cochlear filtering, which will be important in a variety of applications, including audio compression and automatic speech recognition systems. C. Refining measures of cochlear compression in normal and impaired hearing: Additivity and sub-threshold masking effects . "A neural representation of pitch salience in non-primary human auditory cortex revealed with fMRI," J. Neurosci. 24, 6810-6815.