Detection thresholds for brief sounds--are they a measure of auditory intensity integration?

The present study measured how the detection thresholds for two very brief tone or noise bursts depend on the delay between them. The thresholds for the tone burst pairs systematically increase for increasing delays up to a few milliseconds and then reach a constant value. The tone burst thresholds thus reflect a very short-term interaction between the brief signals. Strikingly, the time constant of the interaction appears to scale inversely to the frequency of the tone bursts. The thresholds for the noise burst pairs, on the other hand, remain approximately constant down to the shortest measured delay of less than 1 ms. In contrast to the concept of intensity integration, these results are interpreted in terms of a temporal overlap of the auditory filter responses elicited by two brief, successively presented signals. In a second experiment it was shown that the observed short-term interaction between two brief signals is sensitive to their relative phases, corroborating the conjecture that the interaction takes place at a level prior to the mechanical to neural transduction in the inner ear.