An automatic electric response audiometer

Abstract

Available evoked potential procedures vary widely in how fast and how accurately they assess sensitivity at the audiometric frequencies (250 through 4000 Hz). We will describe a device that can extract this information quickly and automatically. As in Bekesy audiometry, it uses patient responses to control attenuator settings which are then plotted as a function of time. The responses used, however, are the sine‐wave like brain potentials recorded at the scalp during monaural presentation of tone pips at a rate around 40 Hz [Galambos et al., Proc. Natl. Acad. Sci. USA 78, 2643 (1981)]. Cross correlating several hundreds of these with a sinusoidal template yields a number which, depending on whether it is high or low, causes a 5 dB decrease or increase, respectively, in the sound intensity. The procedure is then repeated at the new sound level. A computer processes the responses, performs the statistical computations and resets the attenuator every 5–15 s. A threshold estimate can be obtained in a few minutes; these agree well with the behavioral for alert adults, but when the mind wanders, and during drowsiness and sleep, they can rise by 20–30 dB.