Amplitude modulation thresholds for the parakeet (Melopsittacus undulatus)

Summary Parakeets were tested for the ability to detect sinusoidal amplitude modulation of broad band noise. Instrumental avoidance conditioning and a psychophysical modified method of limits procedure were used to measure the threshold for detecting amplitude modulation at 10 modulation frequencies between 2 and 2,048 Hz. Below about 40 Hz, modulation threshold is independent of modulation rate and noise level. Above 40 Hz, modulation threshold decreases with modulation frequency at the rate of 3 dB/ octave. These results are somewhat different from amplitude modulation functions in humans suggesting different degrees of temporal resolving power in birds and humans. Thresholds for changes in modulation rate are 1–2 orders of magnitude higher than pure tone frequency difference limens.We thank Frank Cusimano, Ann Huessener, Susan Peters, Roberta Pickert, Bill Searcy, Ken Yasukawa and Tim DeVoogd for participating as subjects, and Dick Fay for providing critical comments. This research was supported by grant No. PHS MH31165 from the National Institute of Mental Health to the first author.