Relations of the Human Vertex Potential to Acoustic Input: Loudness and Masking

Abstract

The rate of increase of amplitude of V (vertex) potentials with the SPL [sound pressure level] of tone bursts is very slow. In one experiment, the exponent of the power law was 0. 15 at 250 Hz, 0. 11 at 1000 Hz, and only 0. 08 at 4000 Hz. Individual differences across subjects seemed more important than the interval between stimuli (1 sec vs 3. 2 sec), and variability across trials often obscured the relation to intensity. In the presence of appropriate bands of masking noise, the input-output curves rise abruptly from the masked threshold to approach the unmasked amplitude at a level about 30 dB above the corresponding masked threshold. The effect resembles recruitment of loudness. Tone pips and tone bursts of different frequency that were judged equally loud evoked slow V potentials of approximately equal amplitude. In some subjects, however, bursts of white noise evoked significantly larger responses than equally loud tone bursts or pips. In spite of the partial similarities between them, the amplitude of the V potential and the sensation of loudness are related differently to the parameters of the acoustic stimulus.