Intensity dynamics and loudness change: A review of methods and perceptual processes

In real-world listening domains such as speech and music, acoustic intensity and perceived loudness are dynamic and continuously changing through time. The percept of loudness change in response to continuous increases (up-ramps) and decreases (down-ramps) of intensity has received ongoing empirical and theoretical interest, the result of which has led to conflicting findings from a range of key paradigms. Therefore, the aim of this brief review is to: (a) describe key paradigms used to measure changes in loudness in response to continuous intensity change; (b) identify methodological issues associated with each paradigm; and (c) discuss the mechanisms proposed to explain differences in loudness change when methodological constraints and response biases are controlled. It is concluded that direct and indirect measures of loudness change reflect two distinct aspects of auditory perception. Specifically, magnitude estimation and continuous loudness paradigms reflect changes in perception associated with a ramp's direction and magnitude of intensity change, and empirical evidence supports the conclusion that greater loudness change in response to down-ramps relative to up-ramps is the real-time perceptual outcome. On the other hand, retrospective global judgements of loudness change are disproportionally weighted on end-level intensity rather than magnitude of intensity change. However, an up-ramp-specific effect of duration on global loudness change is evident when end-level response bias is controlled, and this may be associated with end-point time-of-arrival responses to real and apparent looming auditory motion.