Signal detection analyses of delays in neonates' vocalizations

Signal detection analyses were applied to momentary delays in the regular peeping of newborn chicks that occur in response to acoustic stimuli. Pulsing 1000-Hz tones at various intensities were repeatedly presented to chicks at 0 and 4 days posthatch. Durations of delays on both stimulus and control (mock) trials were collected in histograms. These histograms were then used to draw receiver operating characteristics (ROC curves) given variable definitions of what constitutes a "yes" response. Areas under these ROC curves were used to evaluate various ways of measuring the delay, as well as the effects of habituation, intensity, and age. Time to the second poststimulus peep was identified as a sensitive indicator of responsiveness. Habituation decreased responsiveness by about 5% per trial over the first three trials. Each dB of intensity increased responsiveness by about 1%. Maturation increased responsiveness by about 21 dB over 4 days. These ROC curves show that momentary delays in the vocalizations of newborn chickens are appropriate measures of auditory signal detection. Similar analyses could be useful in other psychophysical studies that depend on the changing rate of repetitive responses.