Psychoacoustics of normal adult chickens: thresholds and temporal integration

Three adult female chickens were trained to detect pure tones using a positive reinforcement paradigm. A modified perometer estimation-through sequential testing (PEST) threshold determination procedure was used to measure the audiogram between 250 and 5500 Hz, at 0.1-octave steps over most of the range. For the mean audiogram, threshold increased rapidly below 400 Hz and above 4000 Hz. Between these extremes was a broad low threshold area where thresholds varied between 11 and 23 dB, with the lowest thresholds between 1000 and 2000 Hz. Audiograms were similar for all three subjects over the middle of the frequency range, but there was more variability across subjects at the extreme high and low frequencies. After determination of the audiogram, thresholds for 12 frequencies were measured as a function of stimulus duration (ranging from 16 to 750 ms) to determine a threshold-duration function. Average time constants varied from 148 to 348 ms, increasing with increasing stimulus frequency. Average slopes varied from 2.18 dB per doubling of duration to 2.61 dB per doubling of duration, increasing with increasing stimulus frequency. The increases in slope and time constant with stimulus frequency, while consistent, were small compared to the variability of these parameters across subjects.