Satoshi Amagai
Robert J. Dooling
Tracy L. Kidd
Psych. Dept., Univ. of Maryland, College Park, MD 20742
Shihab Shamma
Univ. of Maryland, College Park, MD 20742
Previous psychoacoustic measures of both critical ratios and critical bands in budgerigars indicate that the size of the auditory filters around 2--4 kHz approach or are even smaller than those of humans. Accordingly, budgerigars should excel at spectral discrimination tasks involving channels around 3 kHz. This study examined the ability of budgerigars to discriminate spectrally rich sounds by using rippled noise stimuli. Three budgerigars were trained in a repeating background procedure using operant conditioning to discriminate between a complex stimulus with a flat spectrum and one that had a sinusoidal ripple imposed on its spectrum. Each stimulus was composed of 201 spectral components logarithmically spaced from 500 Hz to 10 kHz, 100 ms in duration and sampled at 40 kHz. Ripple frequencies between 0.5 and 12 cycles/oct were tested using ripple amplitude steps of 1/2 to 2 dB. Overall levels of the stimuli were varied randomly from 55 dB to 65 dB SPL to remove intensity cues. Ripple amplitude detection thresholds for budgerigars were similar to those measured for humans with budgerigars slightly better at higher ripple frequencies. [Work supported by NIH Grants DC00198 and MH00982.]