Proportion of time vocalising as a metric of vocal activity

A fundamental aspect of describing vocal activity is to quantify its overall level. For instance, everyone agrees that animals become more vocal when they are excited or stressed, but what does it mean to be ‘more vocal’? Increased duration of individual calls and their repetition rate are the most commonly reported temporal markers of arousal, but proportion of time spent vocalising (PTV) appears to increase with arousal more consistently based on my re-analysis of 43 previous studies. From a perceptual perspective, PTV in combination with loudness is well suited to capture the intensity of auditory stimulation. Indeed, it emerged as the best temporal predictor of how much human listeners were distracted and bothered by repeated sounds in recent psychoacoustic experiments. In addition to average PTV calculated from mean call duration and rate, I propose modelling time-dependent instantaneous PTV using simple assumptions about the relevant time scale of arousal modulation or the duration of echoic auditory memory. Thus defined, PTV is a simple, powerful, intuitive, highly informative, and yet under-utilised metric of vocal activity both on longer time scales and within a single episode or call bout.