Activity level and auditory responsiveness in neonatal chickens.

The effects of prestimulus activity levels on auditory responsiveness were evaluated in newborn chickens. Rates of peeping were used as measures of prestimulus activity, and delays in the otherwise ongoing vocalizations were used as measures of responsiveness. Results show increased responsiveness to pure tones at intermediate levels of prestimulus activity. Responsiveness is reduced during periods of high and low activity. The effect is strongest just prior to the stimulus. Similar analyses could be useful in other studies that depend on the changing rate of repetitive responses, such as gross body movements, head turning, heart rate, and perhaps neural potentials. Some of the variability in the responses of young subjects can be controlled by measuring the subject's activity at the time a stimulus is presented.