51 infants were exposed while asleep during the morning and night to periods of 2--5 rain of mixed noise (90--7000 Hz) ; changes in the peripheral circulation were recorded by means of a ttensel Fluvograph on the forehead and the back of the ]eft hand.
At noise levels below 65 dB(B), no infanf showed changes in peripheral resistance; at 70 dB(B) about one-third of the infants and at 80 dB(B) about twothirds showed lowered resistance. At 90 dB(B) vasoconstriction occurred in all cases. There was no difference between day and night recordings. The intensity of the vasoconstriction response was not proportional to the noise stimulus.
The peripheral vasoconstriction regularly ensued a few seconds after the noise started, reaching a maximum during the second minute. On cessation of the noise, the normal level of the peripheral circulation was quickly restored, in many cases even before the noise ceased. The contrasts with the reactions of adults in whom vasoconstriction persists throughout the noise phase.
Infants show alarm reactions to repeated, loud, high-frequency noises and the resulting sympathicotonic reaction persists for several minutes. Clearly, repeated short noise stimuli of this type have a cumulative effect.