Development of absolute thresholds in chickens

Abstract

Absolute auditory thresholds were estimated in chickens at 0 and 4 days after hatching. Momentary suppressions of the chicks'' regular peeping, following the onset of a tone, were used as indications of stimulus detection. In the 1st experiment a staircase procedure was used to estimate thresholds. The absolute thresholds of both ages were the same at low frequencies (250-500 Hz), but at a higher frequencies (1-2 kHz) 4-day-old chicks had lower thresholds than the 0-day-old chicks. The estimates of thresholds at 1 kHz were corroborated in the 2nd experiment with a method of constant stimuli. A more efficient modified method of limits was used to replicate the age by frequency interaction in the 3rd experiment. These changing thresholds are likely to reflect a developmental process somewhere in the auditory system and not some nonsensory artifact for 2 reasons: similar thresholds at low frequencies show that developmental differences are not due to differences in the sensitivity of the testing procedure at the 2 ages and thresholds obtained from the 4-day-old birds are similar to estimates from mature birds. Responsiveness to low frequencies developes before responsiveness to higher frequencies, showing that the development of absolute thresholds is correlated with other measures of functional maturation in the auditory system.