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 1kHz 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 stimuli 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 15-dB 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 diff erent intensity-regions (from 50–65 dB SPL to 70–85 dB SPL). Significant asymmetries were observed across the diff erent frequencies but not for broadband noises. In addition, a significant interaction between the direction of change and the intensity-region was observed for tones and noises. This latter eff ect 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 Experiment 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 rising followed by a falling 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.