Short-latency auditory responses obtained by cross correlation.

Short-latency auditory responses were derived by cross correlation of pseudorandom white noise with averaged scalp potentials in guinea pigs. The cross-correlation functions were characterized by distinct cochlear microphonic and neural components, as distinguished by susceptibility to hypothermia and masking noise. This technique detects only linear, frequency-following responses of the auditory system, and demonstrated neural frequency following up to 3-4 kHz; thresholds were about 30-40 dB spectrum level. While conventional auditory brain stem responses reflect onset neural activity and are most responsive to high-frequency stimuli, cross-correlation responses reflect frequency-following activity, primarily to low frequencies, and thus may represent a complementary method of electrophysiologic assessment of the auditory system. Data are very rapidly acquired, and estimation of responses of limited areas of the cochlea may be possible by off-line digital filtering of cross-correlation functions obtained with broadband noise stimuli.