Isoresponse versus isoinput estimates of cochlear filter tuning

Area of Science:

• Auditory Neuroscience
• Psychoacoustics
• Signal Processing

Background:

• Filter tuning is critical for auditory perception.
• Linear filters are characterized by isoresponse and isoinput measures.
• Nonlinear auditory filters, like the basilar membrane, exhibit compressive responses.

Purpose of the Study:

• To theoretically demonstrate that isoresponse measures yield sharper tuning estimates than isoinput measures for nonlinear filters.
• To practically investigate the implications of this phenomenon on human auditory filter bandwidths (BW(3dB)) at different frequencies.
• To compare BW(3dB) estimates derived from isoresponse and isoinput measures under varying masker conditions.

Main Methods:

• Theoretical analysis of linear and nonlinear filter characteristics.
• Behavioral experiments measuring human auditory filter BW(3dB) using sinusoidal and notched noise forward maskers.
• Inference of cochlear responses and their compressive nature.

Main Results:

• Inferred cochlear responses were compressive for both masker types.
• Isoresponse BW(3dB) estimates were significantly narrower than isoinput estimates at 500 Hz (69 vs. 174 Hz) and 4,000 Hz (280 vs. 464 Hz).
• Isoresponse BW(3dB) decreased with increasing sound level, while isoinput estimates remained relatively constant or increased slightly.

Conclusions:

• Isoresponse measures provide a more accurate representation of auditory filter sharpness due to compressive cochlear nonlinearities.
• Direct comparisons between supra-threshold human tuning (isoresponse) and threshold animal neural tuning require careful consideration.
• Understanding these measurement differences is crucial for accurate auditory modeling and research.