Are Rising Sounds Always Louder? Influences of Spectral Structure and Intensity-Region on Loudness Sensitivity to Intensity-Change Direction

In a previous study, a robust asymmetry in global loudness was observed between rising and falling-intensity 1-kHz tones, pointing out the existence of a mechanism specifically sensitive to sound intensity direction [Ponsot et al., Attention Perception, & Psychophysics, 77(3), 907-920 (2015)]. The properties of this “direction-sensitive” mechanism are further explored in the present study, where its dependence on two stimulus characteristics, the spectral content and the intensity region is examined. In a first experiment, the global loudness of rising and falling-intensity sounds varying over 15dB ranges was assessed in a magnitude estimation task. The ramps had various spectral contents (pure tones from 250 Hz to 8 kHz and broadband noises) and were presented in different intensity-regions (from [50-65 dB SPL] to [70-85 dB SPL]). Significant asymmetries were observed across the different frequencies but not for broadband noises. In addition, a significant interaction between the direction of intensity-change and the region of intensity was observed for tones and noises. This latter effect was specifically addressed in a second experiment using an adaptive loudness-matching procedure, in which asymmetries were inferred from pairwise comparisons, both for 1-kHz tones and for white noises presented in mid and high intensity-regions. As in Exp. 1, greater asymmetries were observed for tones compared to noises; however significant asymmetries were found for noises as well. Furthermore, for both tones and noises, the size of the asymmetries was significantly decreased with the intensity-region when the sound pairs were composed of a falling followed by a rising stimulus. These results are discussed in the light of recent physiological and neuroscience studies showing that spectrally structured looming sounds are treated specially by the brain.