1 Introduction Acoustic cues such as intensity, reverberation, interaural time delay, and Doppler-shifted frequencies provide key information for auditory motion perception (Jenison 1997). However, the dynamic characteristic of intensity change is arguably the most effective for perceived motion in depth (Neuhoff 2004). From the perspective of a listener, a con- tinuous increase in intensity (termed hereafter an up-ramp) can represent, among other things, a `looming' (or approaching) sound source, whereas a continuous decrease in intensity (termed hereafter a down-ramp) is characteristic of a receding sound source. An assumption in studies of these dynamic stimuli is that up-ramps hold greater perceptual salience than down-ramps. Here we investigate this assumption further by focusing on one particular area of psychophysical investigation: the relationship between acoustic intensity dynamics and perceptual overestimation of loudness change. 1.1 An adaptive bias to looming auditory motion An ecological perspective supports the notion that up-ramps are perceptually salient because an approaching sound source in the environment elicits faster processing and appropriate responsive actions to what may be a potentially threatening event (Neuhoff 2001). A receding stimulus does not demand the same behavioural priority. Therefore, behavioural biases in response to looming versus receding motion may provide an advan- tage for organisms able to `err on the side of caution' when a sound source approaches (Neuhoff 2004). For example, in the visual domain humans underestimate the time-to- contact of apparent real-world looming objects, expecting contact significantly earlier than actual contact (Schiff and Oldak 1990). In the auditory domain, humans overestimate loudness change in response to up-ramp tonal stimuli, relative to down-ramps (Neuhoff 1998). Specifically, 1.8 s up-ramp pure tones and a 1.8 s up-ramp synthetic vowel (/ / ösounds like the `a' in `about') are Perceptual overestimation of rising intensity: Is stimulus continuity necessary? Perception, 2010, volume 39, pages 695 ^ 704 Kirk N Olsen, Catherine J Stevens MARCS Auditory Laboratories, University of Western Sydney, South Penrith DC, NSW 1797, Australia; e-mail: k.olsen@uws.edu.au; http://marcs.uws.edu.au Received 7 October 2009, in revised form 28 January 2010; published online 17 May 2010 Abstract. A ``perceptual bias for rising intensity'' (Neuhoff 1998, Nature 395 123 ^ 124) is not dependent on the continuous change of a dynamic, looming sound source. Thirty participants were presented with pairs of 500 ms steady-state sounds corresponding to onset and offset levels of previously used dynamic increasing- and decreasing-intensity stimuli. Independent variables, intensity-change direction (increasing, decreasing), intensity region (high: 70 ^ 90 dB SPL, low: 50^70 dB SPL), interstimulus interval (ISI) (0 s, 1.8 s, 3.6 s), and timbre (vowel, violin) were manipulated as a fully within-subjects design. The dependent variable was perceived loudness change between each stimulus item in a pair. It was hypothesised that (i) noncontinuous increases of intensity are overestimated in loudness change, relative to decreases, in both low-intensity and high-intensity regions; and (ii) perceptual overestimation does not occur when end-levels are balanced. The hypotheses were partially supported. At the high-intensity region, increasing stimuli were perceived to change more in loudness than decreasing-intensity stimuli. At the low-intensity region and under balanced end-level conditions, decreasing-intensity stimuli were perceived to change more in loudness than increasing-intensity stimuli. A significant direction6region interaction varied as a function of ISI. Methodological, sensory, and cognitive explanations for overestimation in certain circumstances are discussed. doi:10.1068/p6592