Vertical Mapping of Auditory Loudness: Loud is High, but Quiet is not Always Low

Abstract

Although the perceptual association between verticality and pitch has been widely studied, the link between loudness and verticality is not fully understood yet. While loud and quiet sounds are assumed to be equally associated crossmodally with spatial elevation, there are perceptual differences between the two types of sounds that may suggest the contrary. For example, loud sounds tend to generate greater activity, both behaviourally and neurally, than quiet sounds. Here we investigated whether this difference percolates into the crossmodal correspondence between loudness and verticality. In an initial phase, participants learned one-to-one arbitrary associations between two tones differing in loudness (82dB vs. 56dB) and two coloured rectangles (blue vs. yellow). During the experimental phase, they were presented with the two-coloured stimuli (each one located above or below a central "departure" point) together with one of the two tones. Participants had to indicate which of the two-coloured rectangles corresponded to the previously-associated tone by moving a mouse cursor from the departure point towards the target. The results revealed that participants were significantly faster responding to the loud tone when the visual target was located above (congruent condition) than when the target was below the departure point (incongruent condition). For quiet tones, no differences were found between the congruent (quiet-down) and the incongruent (quiet-up) conditions. Overall, this pattern of results suggests that possible differences in the neural activity generated by loud and quiet sounds influence the extent to which loudness and spatial elevation share representational content.