Factors affecting the recordability of auditory evoked response component Pb (P1).

The auditory middle latency response (AMLR) is characterized by two positive peaks (Pa, Pb) and two negative peaks (Na, Nb). The unpredictable nature of the second positive peak, Pb or P1, has made its diagnostic use problematic. Our purpose was to determine an appropriate combination of stimulating and recording variables that evoked a repeatable Pb in adults and children. Three experiments were designed to evaluate systematically the amplitude and latency of the Pb as a function of duration, stimulus type (500- and 4000-Hz tone bursts and clicks), repetition rate (0.5, 0.7, 1.1, 2.1, and 5.1/sec), and electrode array. Results showed that a longer duration (60 msec), low-frequency (500-Hz) tone burst consistently evoked the Pb in all subjects. Results also showed that a longer interstimulus interval (1.1/sec) is more likely to evoke the Pb component. Additionally, results showed that Pb is generally largest when recorded from a noninverting electrode at Fz with a noncephalic reference. Finally, results showed that Pb latency is significantly longer and amplitude larger in children than in adults.