Behavioral measures of the critical bandwidth in the chinchilla

A positive-reinforcement behavioral procedure was used to determine masked thresholds in the chinchilla. The critical bandwidth at 1 kHz was estimated in two ways. First, the threshold for a pure tone centered geometrically in bands of noise of constant spectrum level was determined. Thresholds increased with masker bandwidth up to the critical band, beyond which further increases in masker bandwidth produced no further increase in masked threshold. The critical band varied between 205 and 500 Hz in individual subjects. The second method was to measure the threshold of a tone centered between two bands of noise and to determine masked threshold as a function of spacing between maskers. The behavioral data for four chinchillas showed a slow decline in masked threshold as a function of spacing between maskers up to the critical bandwidth, and a very rapid decline as the spacing exceeded the critical bandwidth. The chinchilas showed critical bands at 1 kHz between 320 and 380 Hz. The two methods are compared and differences between obtained critical bandwidth are discussed. [Supported by grants from NSF and NIH.]