Abstract:

Estimates of the filter bandwidths in the avian auditory system have traditionally come from either single-unit tuning curves or psychophysical masking studies using broad (critical ratio) or narrow (critical band) noises---procedures that are known to have certain limitations. The experiment reported here used the notched-noise method for determining the size and shape of the auditory filter at 2.86 kHz---the center of the budgerigar's range of hearing. Three budgerigars were trained by operant conditioning to detect a pure tone in a background of continuous noise and tested daily until thresholds stabilized. Masked thresholds were then obtained for noises of eleven different notch widths (five symmetric, six asymmetric) surrounding 2.86 kHz. Relative equivalent rectangular bandwidths were evaluated using several procedures and these bandwidths were compared to other estimates of filter bandwidths in the budgerigar auditory system from critical ratios, directly measured critical bands, critical modulation frequency, psychophysical tuning curves, and the detection of gaps in pure tones. The size and shape of filter bandwidths in budgerigars will be compared to similar measures on other birds and other vertebrates. [Work supported by NIH Grant Nos. DC-00198 and MH-00982 to RJD.]