Masking effects on ABR waves I and V in infants and adults.

The effects of high- and low-pass masking on waves I and V of the auditory brain stem response (ABR) were measured in normal infants who were 2-4 weeks old, and in adults. The signal was a 4-kHz tone pip presented at 86 dB peak equivalent sound-pressure level (p.e.SPL). The masking patterns were different for latency and amplitude criteria, and were also different for infants and adults. The largest difference between infants and adults was seen in the wave I data. Low-pass maskers were very disruptive of the infant wave I, while little or no effect was noted on the adult wave I. High-pass maskers were very disruptive of the adult wave I, while less of an effect was measured on the infant wave I. The wave V data were similar between groups. Cochlear regions which contribute most importantly to wave I extend up to one octave above the frequency of the signal in adults, and to one-half octave above the signal frequency in infants. The reasons for the differences found between infants and adults are uncertain. Two possible mechanisms which can explain these data are differences in peripheral auditory sensitivity, and differences in tuning characteristics of the auditory system.