Two‐Tone suppression areas in the chinchilla auditory nerve

Abstract

Frequency Threshold Curves (FTC) and two‐tone supression (2TS) areas have been determined for single, primary fibers. 2TS is defined as a 20% or greater decrease in the firing rate evoked by a tone at the unit's characteristic frequency (CF) 10 dB above CF‐threshold associated with the addition of a second variable tone. The shape and size of 2TS areas vary systematically as a function of fiber CF. The low side 2TS areas (second tone below CF) are located outside the limits of the fiber's FTC for high CF units and within the boundaries of the FTC for units with CF of approximately 3 kHz and below. With our criterion, low side 2TS areas are rarely found for low CF units (less than 2 kHz). Whole‐nerve AP tuning curves collected with a forward masking procedure and AP supression areas collected with an unmasking method are similar to the single unit data for probe frequencies above about 4 kHz. Below 4 kHz, AP supression areas are smaller than their unit counterparts. Forward masking AP tuning curves are consistently broader than single unit FTCs.