Relations between frequency selectivity and two-tone rate suppression in lizard cochlear-nerve fibers

Area of Science:

• Auditory Neuroscience
• Bioacoustics
• Sensory Physiology

Background:

• Cochlear nerve fibers display frequency selectivity and two-tone rate suppression (TTRS).
• The basilar papilla in the alligator lizard's cochlea is a model system for studying auditory processing.

Purpose of the Study:

• To investigate the relationship between frequency selectivity and TTRS in alligator lizard cochlear-nerve fibers.
• To characterize the frequency threshold contour (FTC) and iso-TTRS contour (ITC) and their dependence on characteristic frequency (CF).

Main Methods:

• Measurements of frequency threshold contours (FTCs) for single tones.
• Measurements of iso-TTRS contours (ITCs) for two simultaneous tones.
• Analysis of FTC and ITC features in relation to characteristic frequency (CF).

Main Results:

• FTCs and ITCs systematically vary with the fiber's characteristic frequency (CF).
• Notches and break frequencies in FTCs, and lobes in ITCs, show systematic variations with CF.
• Detailed shapes of FTCs and ITCs are closely related, with interdigitating features and associated slopes.

Conclusions:

• Sharp frequency selectivity and TTRS in alligator lizard cochlear fibers are closely related.
• These auditory phenomena likely arise from a common underlying cochlear mechanism.