Acoustic evoked responses in newborn infants: the influence of pitch and complexity of the stimulus

Abstract

1. 1. Averaged evoked responses were recorded bipolarly from T 5-C z and T 6-C z in groups (I,II) of human newborns during acoustic stimulation. 2. 2. Group I was stimulated with five sounds: sine and square wave tones at 125 and 1000 c/sec, respectively, and a recorded female voice saying “baby”. Group II was stimulated with four sounds: the 125 c/sec square wave, white noise of approximately equal band width (“wide band”) and two filtered components of it (“low band” and “high band”), respectively. 3. 3. The response most consistently present following stimulation was the N 2 wave. In Group I evoked N 2 responses of decreasing amplitude were obtained to: the 125 c/sec square wave, the voice, the 1000 c/sec square wave, the 125 c/sec and 1000 c/sec sine waves, respectively. In Group II the order of magnitude from greatest to smallest was: 125 c/sec square wave, wide band noise, low band noise and high band noise. 4. 4. The results support the hypothesis proposed in an earlier publication, that the degree of behavioural and physiological response to sound in a newborn infant is proportional to the length of basilar membrane excited by the stimulus.